Letter

Nature 461, 802-808 (8 October 2009) | doi:10.1038/nature08490; Received 22 August 2008; Accepted 8 September 2009

A genome-wide linkage and association scan reveals novel loci for autism

Lauren A. Weiss1,2,77,75, Dan E. Arking3,77 & The Gene Discovery Project of Johns Hopkins & the Autism Consortium

  1. Center for Human Genetic Research, Massachusetts General Hospital and Harvard Medical School, Boston, Massachusetts 02114, USA.
  2. Broad Institute of MIT and Harvard, Cambridge, Massachusetts 02142, USA.
  3. Center for Complex Disease Genomics, McKusick-Nathans Institute of Genetic Medicine, Johns Hopkins University, Baltimore, Maryland 21205, USA.
  4. Institute for Juvenile Research, Department of Psychiatry, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
  5. Center for Neurodegeneration and Experimental Therapeutics, University of Alabama School of Medicine, Birmingham, Alabama 35294, USA.
  6. Developmental Medicine Center, Children’s Hospital Boston, Boston, Massachusetts 02115, USA.
  7. Division of Genetics, Children’s Hospital Boston and Harvard Medical School, Boston, Massachusetts 02115, USA.
  8. Special Education Organization, Tehran, Iran.
  9. Department of Psychiatry, University of Oxford, Warneford Hospital, Headington, Oxford OX3 7JX, UK.
  10. Newcomen Centre, Guy’s Hospital, London SE1 9RT, UK.
  11. Battelle Center for Mathematical Medicine, The Research Institute at Nationwide Children’s Hospital and The Ohio State University, Columbus, Ohio 43205, USA.
  12. Child and Adolescent Mental Health, University of Newcastle, Sir James Spence Institute, Newcastle upon Tyne NE1 4LP, UK.
  13. INSERM U952, Université Pierre et Marie Curie, 75005 Paris, France.
  14. Department of Child and Adolescent Psychiatry, Psychosomatics and Psychotherapy, J.W. Goethe University Frankfurt, 60528 Frankfurt, Germany.
  15. Department of Child and Adolescent Psychiatry, Institute of Psychiatry, London SE5 8AF, UK.
  16. Autism Research Unit, The Hospital for Sick Children and Bloorview Kids Rehabilitation, University of Toronto, Toronto, Ontario M5G 1Z8, Canada.
  17. Department of Pediatrics and Psychology, Dalhousie University, Halifax, Nova Scotia B3K 6R8, Canada.
  18. Laboratory of Molecular Neuropsychiatry, Seaver Autism Center for Research and Treatment, Departments of Psychiatry, Genetics and Genomic Sciences, and Neuroscience, Mount Sinai School of Medicine, New York, New York 10029, USA.
  19. Department of Human Genetics, University of California–Los Angeles School of Medicine, Los Angeles, California 90095, USA.
  20. Psychiatry Department, University of Utah Medical School, Salt Lake City, Utah 84108, USA.
  21. Autism and Communicative Disorders Centre, University of Michigan, Ann Arbor, Michigan 48104, USA.
  22. Miami Institute for Human Genomics, University of Miami, Miami, Florida 33136, USA.
  23. Departments of Psychology and Psychiatry, University of Washington, Seattle, Washington 98195, USA.
  24. Department of Child Psychiatry, University Medical Center, Utrecht 3508 GA, The Netherlands.
  25. University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 19104-6100, USA.
  26. School of Medicine and Medical Science University College, Dublin 4, Ireland.
  27. Division of Psychiatry, McGill University, Montreal, Quebec H3A 1A1, Canada.
  28. Autism Genetics Group, Department of Psychiatry, School of Medicine, Trinity College, Dublin 8, Ireland.
  29. Department of Neurology, University of California–Los Angeles School of Medicine, Los Angeles, California 90095, USA.
  30. Department of Psychiatry and Behavioural Neurosciences, McMaster University, Hamilton, Ontario L8N 3Z5, Canada.
  31. Academic Department of Child Psychiatry, Booth Hall of Children’s Hospital, Blackley, Manchester M9 7AA, UK.
  32. Centre for Human Genetics Research, Vanderbilt University Medical Centre, Nashville, Tennessee 37232, USA.
  33. Child and Adolescent Psychiatry and Child Development, Stanford University School of Medicine, Stanford, California 94304, USA.
  34. Deutsches Krebsforschungszentrum, Molekulare Genomanalyse, 69120 Heidelberg, Germany.
  35. Centre for Integrated Genomic Medical Research, University of Manchester, Manchester M13 9PT, UK.
  36. Department of Pediatrics, McMaster University, Hamilton, Ontario L8S 3Z5, Canada.
  37. Centre d’Eudes et de Recherches en Psychopathologie, University de Toulouse Le Miral, Toulouse 31058, France.
  38. Wellcome Trust Centre for Human Genetics, University of Oxford, OX3 7BN, UK.
  39. University Department of Child Psychiatry, Athens University, Medical School, Agia Sophia Children’s Hospital, Athens 115, Greece.
  40. Department of Medicine, School of Epidemiology and Health Science, University of Manchester, Manchester M13 9PT, UK.
  41. Carolina Institute for Developmental Disabilities, University of North Carolina, Chapel Hill, North Carolina 27599-3366, USA.
  42. Social, Genetic and Developmental Psychiatry Centre, Institute Of Psychiatry, London SE5 8AF, UK.
  43. Pathology and Laboratory Medicine, University of Pennsylvania, Philadelphia, Pennsylvania 19108, USA.
  44. The Centre for Applied Genomics and Program in Genetics and Genome Biology, The Hospital for Sick Children and Department of Molecular Genetics, University of Toronto, Toronto, Ontario M5G 1L7, Canada.
  45. Department of Pediatrics and Howard Hughes Medical Institute Carver College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
  46. Vanderbilt Kennedy Center and Center for Molecular Neuroscience, Vanderbilt University, Nashville, Tennessee 37232, USA.
  47. Child Study Centre, Yale University, New Haven, Connecticut 06510, USA.
  48. Department of Psychiatry, Carver College of Medicine, Iowa City, Iowa 52242, USA.
  49. Department of Biostatistics and Medicine, University of Washington, Seattle, Washington 98195, USA.
  50. Department of Pediatrics, University of Alberta, Edmonton, Alberta T6G 2J3, Canada.
  51. Instituto Nacional de Saude Dr Ricardo Jorge Instituto Gulbenkian de Cîencia Lisbon, 1600-560 Portugal.
  52. Hospital Pediatrico de Coimbra, Coimbra, 3000-300 Portugal.
  53. Department of Child and Adolescent Psychiatry, Goteborg University, Goteborg S41345, Sweden.
  54. INSERM U995, Department of Psychiatry, Groupe hospitalier Henri Mondor-Albert Chenevier, AP-HP, Créteil, France.
  55. Department of Medicine, University of Washington, Seattle, Washington 98195, USA.
  56. Stella Maris Institute, Department of Child and Adolescent Neurosciences, 56018 Calambrone (Pisa), Italy.
  57. Department of Psychiatry, Indiana University School of Medicine, Indianapolis 46202, USA.
  58. Department of Biology, University of Bologna, 40126 Bologna, Italy.
  59. Autism Speaks, New York, New York 10016, USA
  60. Department of Neurology and Howard Hughes Medical Institute, Beth Israel Deaconess Medical Center, Boston, Massachusetts 02215, USA.
  61. Department of Child Psychiatry, Istanbul Faculty of Medicine, Istanbul University, 34452 Istanbul, Turkey.
  62. Department of Neurosciences and Pediatrics, King Faisal Specialist Hospital and Research Centre, Jeddah 11211, Kingdom of Saudi Arabia.
  63. Clinical Neurosciences & Pediatrics, Brown University School of Medicine, Providence, Rhode Island, USA.
  64. Department of Neurology, Combined Military Hospital, Lahore, Pakistan.
  65. Kuwait Center for Autism, Kuwait City 73455, Kuwait.
  66. Department of Anatomy and Neurobiology, Boston University School of Medicine, Boston, Massachusetts 02118, USA.
  67. Department of Child Psychiatry and Department of Clinical Genetics, Oulu University Hospital and Oulu University, Oulu FIN-90029, Finland.
  68. Medical Genetic Diagnosis Department, National Institute for Genetic Engineering and Biotechnology, Tehran, Iran.
  69. Casa de Corazon, Taos, New Mexico 87571, USA.
  70. Centre de recherche du CHUM, Hôpital Notre-Dame, Montréal, H2L 4M1 Quebec, Canada.
  71. Sainte-Justine Hospital Research Center, Universite de Montreal, Montreal, H3T 1C5 Quebec, Canada.
  72. Department of Medical Genetics, University of Helsinki, Helsinki, FIN-00014, Finland.
  73. Department of Molecular Medicine, National Public Health Institute, Helsinki, FIN-00014, Finland.
  74. Wellcome Trust Sanger Institute, Hinxton CB10 1SA, UK.
  75. Present addresses: Department of Psychiatry, Institute for Human Genetics, Center for Neurobiology and Psychiatry, UCSF, San Francisco, California, USA (L.A.W.); Department of Molecular Biology, Cell Biology and Biochemistry, and Institute for Brain Science, Brown University, Providence, Rhode Island, USA (E.M.M.).
  76. Deceased.
  77. These authors contributed equally to this work.
  78. Lists of participants and affiliations appears at the end of the paper.

Correspondence to: Correspondence and requests for materials should be addressed to A.C. (Email: aravinda@jhmi.edu) or M.J.D. (Email: mjdaly@chgr.mgh.harvard.edu).

Top

Although autism is a highly heritable neurodevelopmental disorder, attempts to identify specific susceptibility genes have thus far met with limited success1. Genome-wide association studies using half a million or more markers, particularly those with very large sample sizes achieved through meta-analysis, have shown great success in mapping genes for other complex genetic traits. Consequently, we initiated a linkage and association mapping study using half a million genome-wide single nucleotide polymorphisms (SNPs) in a common set of 1,031 multiplex autism families (1,553 affected offspring). We identified regions of suggestive and significant linkage on chromosomes 6q27 and 20p13, respectively. Initial analysis did not yield genome-wide significant associations; however, genotyping of top hits in additional families revealed an SNP on chromosome 5p15 (between SEMA5A and TAS2R1) that was significantly associated with autism (P = 2×10-7). We also demonstrated that expression of SEMA5A is reduced in brains from autistic patients, further implicating SEMA5A as an autism susceptibility gene. The linkage regions reported here provide targets for rare variation screening whereas the discovery of a single novel association demonstrates the action of common variants.

For a high-resolution genetic study of autism, we selected families with multiple affected individuals (multiplex) from the widely studied Autism Genetic Resource Exchange (AGRE) and US National Institute for Mental Health (NIMH) repositories (Supplementary Methods and Supplementary Table 1). Although the phenotypic heterogeneity in autism spectrum disorders (ASDs) is extensive, in our primary screen we selected families in which at least one proband met Autism Diagnostic Interview-Revised (ADI-R) criteria for diagnosis of autism and included additional siblings in the same nuclear family affected with any autism spectrum disorder. We previously reported an early copy number analysis that revealed a significant role for microdeletion and duplication of 16p11.2 in ASD causation2; here, we present extensive genome-wide linkage and association analyses performed with this high density of SNPs and identify independent and novel genome-wide significant results by both linkage and association analyses.

We combined families and samples from two sources for the primary genetic association screen. The AGRE sample included nearly 3,000 individuals from over 780 multiplex autism families in the AGRE collection3 genotyped at the Broad Institute on the Affymetrix 5.0 platform, which includes over 500,000 SNPs. The NIMH sample included a total of 1,233 individuals from 341 multiplex nuclear families (258 of which were independent of the AGRE sample) genotyped at the Johns Hopkins Center for Complex Disease Genomics on Affymetrix 5.0 and 500K platforms, including the same SNP markers as were genotyped in the AGRE sample.

Before merging, we carefully filtered each data set separately to ensure the highest possible genotype quality for analysis, because technical genotyping artefacts can create false positive findings. We therefore examined the distribution of χ2 values for the highest quality data, and used a series of quality control (QC) filters designed to identify a robust set of SNPs, including data completeness for each SNP, Mendelian errors per SNP and per family, and a careful evaluation of inflation of association statistics as a function of allele frequency and missing data (see Methods). As 324 individuals were genotyped at both centres, we performed a concordance check to validate our approach. After excluding one sample mix-up, we obtained an overall genotype concordance between the two centres of 99.7% for samples typed on 500K at Johns Hopkins University and 5.0 at the Broad Institute and 99.9% for samples run on 5.0 arrays at both sites. The combined data set, consisting of 1,031 nuclear families (856 with two parents) and a total of 1,553 affected offspring, was used for genetic analyses (Supplementary Table 1). These data were publicly released in October 2007 and are directly available from AGRE and NIMH.

For linkage analyses, the common AGRE/NIMH data set was further merged with Illumina 550K genotype data generated at the Children’s Hospital of Philadelphia (CHOP) and available from AGRE, adding ~300 nuclear families (1,499 samples). We used the extensive overlap of samples between the AGRE/NIMH and the CHOP data sets (2,282 samples) to select an extremely high quality set of SNPs for linkage analysis. Specifically, we only included SNPs genotyped in both data sets with >99.5% concordance and≤1 Mendelian error.

Linkage analysis involving high densities of markers, where clusters of markers are in linkage disequilibrium (LD), can falsely inflate the evidence for genetic sharing among siblings when neither parent is genotyped4. To alleviate these concerns, we analysed a pruned set of 16,311 highly polymorphic, high-quality autosomal SNPs which were filtered to remove any instances in which two nearby markers were correlated with r2>0.1, providing a marker density of ~0.25cM (see Methods). In this analysis of 878 families, four genomic regions showed LOD scores in excess of 2.0 and one region, 20p13, exceeded the formal genome-wide significance threshold of 3.6 (ref. 5) (maximum LOD, 3.81; Fig. 1a and Supplementary Table 2). Restricting analysis to only those families with both parents genotyped (784 families) showed that these results are not an artefact of missing parental data (Fig. 1b). We further tested the stability of these results by varying the recombination map and halving the marker density by placing every other marker into two non-overlapping SNP sets (Methods Summary); all analyses showed consistent and strong linkage to the same regions (data not shown).

Figure 1: Genome-wide linkage results.
Figure 1 : Genome-wide linkage results. Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com

a, The genome-wide linkage results are shown, with the orange line indicating non-parametric linkage (NPL) LOD = 3 and the yellow line indicating NPL LOD = 2. b, Four chromosomes with LOD>2. The black and blue lines indicate results from families with both parents genotyped and all families, respectively. The green line indicates information content (right-hand y axis). The red circle indicates the position of the centromere.

High resolution image and legend (172K)Download PowerPoint slide (664K)

Slides may be downloaded for educational use, according to the terms described in Nature Publishing Group's licensing policy.


We used the transmission disequilibrium test (TDT) across all SNPs passing quality control in the complete family data set for association analyses as the TDT is not biased by population stratification. We estimated a threshold for genome-wide significance using both permutation (P<2.5×10-7) and estimating the effective number of tests (P<3.4×10-7), and use the more conservative here (see Methods). No SNP met criteria for genome-wide significance at P<2.5×10-7. However, we observed an excess of independent regions associated at P<10-5 (6 observed versus 1 expected) and P<10-4 (30 observed versus 15 expected) despite the lack of overall statistical inflation (λ = 1.03, Supplementary Fig. 1), suggesting that common variants in autism exist, but that our initial scan did not have sufficient statistical power to identify them definitively (Table 1 and Supplementary Fig. 2).


For the TDT associations with P<10-4, we additionally used the cases that were excluded from the TDT due to missing parental data. We matched 90 independent and unrelated cases with 1,476 NIMH control samples genotyped on the Affymetrix 500K arrays6, and performed case-control association analysis (Supplementary Table 3), combining these results with the TDT data. Promisingly, we now observed eight SNPs (in seven independent regions) with association at P<10-5 (Table 1). Of note, comparing Caucasian with non-Caucasian samples in the AGRE/NIMH data set, we did not observe significant heterogeneity for top results.

Our strongest associations were at chromosome 4q13 (rs17088254, P = 8.5×10-6) between CENPC1, a centromere autoantigen, and EPHA5, an ephrin receptor potentially involved in neurodevelopment; at 5p15 (rs10513025, P = 1.7×10-6) in the EST DB512398, located between SEMA5A and TAS2R1; at 6p23 (rs7766973, P = 6.8×10-7) in JARID2, an orthologue of the mouse jumonji gene, encoding a nuclear protein essential for embryogenesis, especially neural tube formation; at 9p24 (rs4742409, P = 7.9×10-6) between PTPRD, a protein tyrosine phosphatase involved in neurite outgrowth, and JMJD2C (also called KDM4C), a jumonji-domain containing protein involved in tri-methyl-specific demethylation; at 9q21 (rs952834, P = 7.8×10-6) between ZCCHC6, a zinc finger and CCHC domain containing protein, and GAS1, growth-arrest-specific protein; at 10q21 (rs7923367, P = 3.4×10-6) in CTNNA3, α3 catenin, which may be involved in the formation of stretch-resistant cell–cell adhesion complexes; and two SNPs on 11p14 (rs12293188, P = 1.1×10-6; rs16910194, P = 3.7 × 10-6) in GAS2, a caspase-3 substrate that has a role in regulating microfilament and cell shape changes during apoptosis and can modulate cell susceptibility to p53-dependent apoptosis by inhibiting calpain activity (Table 1).

To confirm whether any of these top results might indicate true susceptibility loci, we attempted to replicate these signals, as well as others with P<10-4 in the initial TDT that met stringent genotyping quality criteria (Supplementary Table 3). We used several data sources to replicate the association results. First, we used additional autism family samples (318 trios collected by investigators of the Autism Consortium and in Montreal) with genome-wide Affymetrix 5.0/500K array data also genotyped at the Genetic Analysis Platform of the Broad Institute using the same conditions, QC and analysis pipelines (Methods).

Second, independent Autism Genome Project (AGP) families, along with a set of Finnish families and a set of Iranian trios, were used for replication of our top findings (n = 1,755 trios). Two Sequenom replication pools were designed, attempting to include as many of the regions associated at P<10-4 as possible. The full set of SNPs considered and those successfully genotyped are shown in Supplementary Table 3, with linkage disequilibrium (r2) noted for SNPs selected as proxies for Affymetrix markers. One of the eight SNPs with P<10-5 (rs10513025) that failed in this Sequenom assay was subsequently replaced in a subset of AGP samples with a TaqMan assay. This assay showed 99.89% concordance with Affymetrix genotypes in the overlapping AGRE-NIMH samples (2,797 out of 2,800 concordant genotypes), with manual review of the Affymetrix genotype calls also confirming the marker to be of extremely high quality (Supplementary Fig. 4). In the independent replication effort, only rs10513025 was associated with P<0.01 (Table 1).

Combining the scan and replication data, only rs10513025 met criteria for genome-wide significance defined by LD and permutation analyses (P<2.5×10-7). To increase coverage of this region and fill in missing genotypes and SNPs that failed quality control, we performed imputation analysis. rs10513026 was highly (but not perfectly) correlated to the replicated chromosome 5 SNP (rs10513025) and showed even stronger association than originally observed with rs10513025 (Supplementary Fig. 3). These and several other promising SNPs were directly genotyped in the original scan samples and, in fact, showed higher levels of significance (Table 2). Direct genotyping confirmed that rs10513026 showed stronger association than rs10513025 (P-value 4.5×10-6 versus 9.8×10-6 in the re-genotyped scan trios), increasing the significance of this observation further. Several other promising results from this analysis were genotyped in a subset of scan samples, and, of note, the top SNP in imputation analysis (rs10874241, imputation P = 9.8×10-7, odds ratio (OR) = 0.43) showed consistent results (OR = 0.4, P = 4×10-7) when directly genotyped (Supplementary Table 4).


rs10513025 and neighbours are on chromosome 5p15 in a region of LD containing several other ESTs and TAS2R1, a bitter taste receptor (Supplementary Fig. 3). The SNPs are ~80kb upstream of semaphorin 5A (SEMA5A), a gene implicated in axonal guidance and known to be downregulated in lymphoblastoid cell lines of autism cases versus healthy controls7. An independent study at Children’s Hospital Boston using whole blood (S.W.K., L.K. and Z.K., manuscript in preparation) confirms this lower expression (P = 0.0034) of SEMA5A in autism cases versus controls. To evaluate the role of this locus in autism pathogenesis more completely, we evaluated the entirety of 5p15 for copy-number variation. Despite excellent probe coverage throughout the locus, no common or rare copy number variants were detected in the entire AGRE scan in the region of LD surrounding the associated SNPs and the entire SEMA5A locus including 250kb up- and downstream (see Methods).

To test directly SEMA5A expression in brains from autistic patients, tissue samples from 20 cases with a primary diagnosis of autism and 10 controls were obtained through the Autism Tissue Program and the Harvard Brain Bank. Samples were dissected from Brodmann area 19 of the occipital lobe cortex, a region demonstrating differences between autism cases and controls in functional imaging studies, and subjected to quantitative PCR8. SEMA5A expression, determined relative to MAP2 (neuron specific), was significantly lower in autism brains than controls after adjustment for the age at brain acquisition, post-mortem interval and sex (P = 0.024, Fig. 2).

Figure 2: SEMA5A expression in autism brains.
Figure 2 : SEMA5A expression in autism brains. Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com

SEMA5A gene expression is shown relative to MAP2. Diamonds indicate individual expression levels for each sample; error bars indicate standard error (s.e.).

High resolution image and legend (70K)Download PowerPoint slide (451K)

Slides may be downloaded for educational use, according to the terms described in Nature Publishing Group's licensing policy.


We also analysed our data for association signals at candidate genes or regions with previous evidence of involvement in autism. Although there are few well-replicated associations of biological candidate genes, there are many rare genetic variants, diseases and syndromes associated with autism. Most of these loci have not been systematically assessed to see whether common variation in the gene or region might contribute to autism. We assessed four categories of candidate loci: (1) genes with previous evidence for association with common variation; (2) genes implicated by rare variants leading to autism; (3) genes causing Mendelian diseases associated with autism; and (4) regions where microdeletion or microduplication syndromes are associated with autism. For each gene, we included all SNPs passing basic quality criteria within 2kb of the transcript.

Overall, there were no compelling results in these sets (all P>10-4), considering the number of SNPs tested, and only two regions met criteria for region-wide (only SNPs in that gene/region considered) or set-wide (for example, all candidate regions in the set of common variant genes considered) significance by permutation testing (Supplementary Table 5). MECP2 (Rett syndrome) met criteria for region-wide association (P = 0.0071, 5 SNPs, Supplementary Table 5). Moreover, the Williams syndrome region was borderline for set-wide significance (P = 0.051, Supplementary Table 5). One SNP in particular showed strong association (rs2267831, P = 0.00012, OR = 0.56)—as this was a rare SNP with undertransmission of the minor allele, we genotyped a subset of families and observed similar, slightly less significant distortion (OR = 0.61). The SNP is located within GTF2IRD1, a transcription factor within the critical region for the Williams syndrome cognitive behavioural profile9, 10, 11.

There seems to be little overlap between the regions of strongest linkage and association in this study. A more detailed assessment of SNP and haplotype association in the most significant linkage regions did not yield common variation that could explain the evidence for linkage (Supplementary Table 6). This is an expected outcome if linkage signals arise from rare, high penetrance variation (for which the genotyping arrays do not offer an adequate proxy) whereas association is sensitive to common variation with lower penetrance (that cannot be detected by linkage). For example, a 0.3% variant that increases risk by tenfold would readily be picked up by this informative linkage scan, but would very likely not be assessed by the common SNPs on the Affymetrix 5.0 array; by contrast, the modest and protective impact of the 5% variant at the SEMA5A rs10513025 creates no detectable excess allele sharing among siblings but is strongly detected by association.

During review of this manuscript, another genome-wide association study (GWAS) was published which identified significant association to SNPs on chromosome 5p1412. Although there was significant overlap between study samples, each of these scans contained a large set of unique families, so we sought to evaluate independent evidence of the top SNP (rs4307059) reported at 5p14. This SNP happens to be directly genotyped by both Affymetrix and Illumina platforms. We have a sizable number (n = 796) of affected subjects with two parents genotyped (and of predominantly similar European background). However, we observed no support for association at this locus (T:U 354:335 in favour of the minor allele, a trend in the opposite direction as reported).

Autism genes have been difficult to identify, despite the high heritability of autism spectrum disorders. Up to 10% of autism cases may be due to rare sequence and gene dosage variants, for example, mutations in NRXN1, NLGN3/NLGN4, SHANK3 and copy number variants at 15q11-q13 and 16p11.2. A number of diseases of known aetiology, including Rett syndrome, fragile X syndrome, neurofibromatosis type I, tuberous sclerosis, Potocki–Lupski syndrome, and Smith–Lemli–Opitz syndrome are also associated with autism1, 13. However, the remaining 90% of autism spectrum disorders, although highly familial, have unknown genetic aetiology. A genome-wide linkage study using the Affymetrix 10K SNP array to genotype over 1,000 families found no genome-wide significant linkage signals, but documented suggestive linkage at 11p12-p13 and 15q23-q25 and reinforced a modest role for rare copy-number variants14.

Many complex diseases have recently had great success with GWAS approaches, but most identified modest effects with odds ratios less than 1.3 (http://www.genome.gov/26525384). Our association analysis has excellent statistical power (>80%) to find effects of relatively common alleles (0.01–0.25 in frequency) explaining 1% of the variance in autism at the genome-wide significant level. It is near-perfectly powered for alleles of SNPs present on the array (or perfectly proxied) down to 1% at the replication cutoff P<10-4, assuming additive background genetic variance of 0.8 and shared environmental variance of 0.05 with prevalence of 0.006. One of the advantages of a family-based association test is that we avoid false positive results generated by population stratification, and in addition, we have performed careful quality control to reduce the chances of being misled by technical artefacts. However, the SNP coverage of the Affymetrix 5.0 chips is incomplete; in fact, a recent re-sequencing survey suggests that these arrays assay only 57% of variants with minor allele frequency (MAF) >5% at r2 = 0.8 (ref. 15). We therefore cannot exclude untested variation of large effect in autism. The linkage analysis, assuming a fully informative marker in 800 sibling pairs, should detect sibling allele sharing of at least 55.125%16.

Our linkage analysis revealed two novel regions of linkage, 6q27 (LOD = 2.94) and 20p13 (LOD = 3.81), with the latter formally exceeding the threshold for genome-wide significance. There is some overlap between the more modest signals (LOD >2 on chromosome 15 and chromosome 17) and previously reported suggestive linkage signals, but little overlap with the most promising regions of common SNP association. This suggests that the regions of the genome showing linkage may harbour rare variation, potentially with allelic heterogeneity across families, which would require re-sequencing to uncover, as has been demonstrated for the 7q35 region17, 18, 19. Interestingly, several of these regions overlap with rare syndromes or genetic events known to be strong risk factors for autism. For example, an autism case with a translocation disrupting 15q25 has been reported, whereas the 17p region overlaps the Smith–Magenis and Potocki–Lupski syndrome region.

The initial TDT analysis of this large multiplex autism data set did not reveal any associations meeting criteria for genome-wide significance, suggesting that there are not many common loci of moderate to large effect size even in a highly heritable disorder like autism. Nevertheless, replication data in our study identified a novel locus with genome-wide significant evidence for association to autism. In addition, several other SNPs in the region show similarly strong association (rs10513026, rs16883317). We ascertained a large replication sample from independent family studies with a replication at P = 0.0061 and meta-analysis showed this association (P = 2.12×10-7) to meet criteria for genome-wide association in our experiment. This region on chromosome 5 harbours the gene encoding the bitter taste receptor, TAS2R1, and several uncharacterized ESTs and is adjacent to SEMA5A, a member of the semaphorin axonal guidance protein family, which has shown downregulated expression in transformed B lymphocytes from autism samples7. We have further extended this finding by directly demonstrating lowered SEMA5A gene expression in autism brain tissue. This is an attractive candidate gene given that its protein is a bi-functional guidance molecule, which is both attractive and inhibitory for developing neurons. Interestingly, the SEMA5A receptor is plexin B3, which also signals through the tyrosine kinase MET, a previously reported autism susceptibility gene20, 21.

Finally, we investigated whether different classes of genes or regions—loci previously implicated by functional or positional candidate gene association studies, rare variants implicated in autism, Mendelian disorder genes with association to autism, or regions of copy number variation associated with autism—showed association with common alleles included in our marker set. Although there were several nominally significant associations, only the Williams syndrome region (one SNP in GTF2IRD1) was borderline statistically significant (P = 0.051), after correcting for the microdeletion/duplication syndrome regions tested. In the category of Mendelian disorders associated with autism, MECP2, the gene for Rett syndrome, showed region-wide statistical significance. These results raise the possibility that Rett and Williams syndrome genes may contribute more generally to autism spectrum disorders. Although the genes in which common variation has been reported to be associated with autism do not show evidence for association, this cannot be interpreted as failure to replicate previous results in all cases, because much of the variation reported as associated is not captured on the Affymetrix platform (for example, length polymorphisms, microsatellites, untagged SNPs such as the promoter variant at MET21). Instead, despite a high density of markers, our results suggest that we did not identify additional common variation with evidence for association. Overall however, our results indicate that these postulated candidate regions, mostly based on rare events known to cause autism, are not among the regions with common alleles having the strongest risk effects for autism.

Interestingly, both our linkage and association analyses, from the primary and replication analyses, suggest that low-frequency (<0.05) minor alleles may be common in autism. Intriguingly, the linkage studies reveal low-frequency susceptibility alleles whereas the association analyses have uncovered rare alleles with odds ratios less than 0.6 (the common alleles in the population associated with increased risk for autism). This can occur when the ancestral allele, that was previously neutral or beneficial, now has detrimental effects revealed by an evolutionarily recent environment, or when a pleiotropic function of the allele is selectively advantageous, or when this variation is hitch-hiking on a shared haplotype with a distinct beneficial allele22. However, it is worth noting that our study design of ascertaining multiplex families is not well powered to identify loci under this genetic model of common major alleles associated with autism susceptibility.

We report genome-wide significant linkage as well as an association of common genetic variation with autism. Our results will require follow-up to identify the functional variation in the linkage and association regions that we report here and to probe the functions of the relatively unstudied transcripts implicated. These results could provide completely novel insight into the biology and pathogenesis of a common neurodevelopmental disorder.

Top

Methods Summary

Samples and genotyping

Our primary samples are from the AGRE and NIMH Repositories. Replication with Affymetrix technology included NIMH controls, families collected by members of the Autism Consortium, and families ascertained from Montreal. Replication with Sequenom technology included the Autism Genome Project, Finnish, and Iranian subsets of Autism Consortium investigator-collected families. Details of the ascertainment for each sample collection, genotyping and quality control processes can be found in Methods.

Linkage and association analysis

The linkage analysis was conducted with a pruned autosomal SNP set (see Methods for details of marker selection) and chromosome X set (670 SNPs) using the cluster option in MERLIN/MINX (r2 < 0.1)23, yielding 16,581 independent markers. We performed confirmatory analysis on non-overlapping data sets by selecting alternative SNPs.

Association analysis was performed in PLINK24. The basic association test was a transmission disequilibrium test (TDT), and the extra cases versus controls analysis was performed by allelic association, after excluding cases that were not well matched to the controls, based on multi-dimensional scaling (λ < 1.1). Combining the TDT and case-control tests was performed using expected and observed allele counts by the formula Zmeta = (∑exp- ∑obs)/√∑var. Meta-analysis of AGRE/NIMH and replication data was performed using the statistic (ZAGRE/NIMH+Zreplication)/√2. Gene-set analysis was performed in PLINK using the set-based TDT. Imputation-based association was performed in PLINK with the proxy-tdt command, using the HapMap CEU parent samples as the reference panel and information score >0.8. Haplotype analysis in the linkage regions was performed using 5-SNP sliding windows, as implemented in PLINK hap-tdt. See Methods for details of determination of genome-wide significance thresholds.

Full methods accompany this paper.

Top

References

  1. Abrahams, B. S. & Geschwind, D. H. Advances in autism genetics: on the threshold of a new neurobiology. Nature Rev. Genet. 9, 341–355 (2008) | Article
  2. Weiss, L. A. et al. Association between microdeletion and microduplication at 16p11.2 and autism. N. Engl. J. Med. 358, 667–675 (2008) | Article | PubMed | ChemPort |
  3. Geschwind, D. H. et al. The autism genetic resource exchange: a resource for the study of autism and related neuropsychiatric conditions. Am. J. Hum. Genet. 69, 463–466 (2001) | Article | PubMed | ISI | ChemPort |
  4. Abecasis, G. R. & Wigginton, J. E. Handling marker-marker linkage disequilibrium: pedigree analysis with clustered markers. Am. J. Hum. Genet. 77, 754–767 (2005) | Article | PubMed | ISI | ChemPort |
  5. Lander, E. & Kruglyak, L. Genetic dissection of complex traits: Guidelines for interpreting and reporting linkage results. Nature Genet. 11, 241–247 (1995) | Article
  6. Sklar, P. et al. Whole-genome association study of bipolar disorder. Mol. Psychiatry 13, 558–569 (2008) | Article | PubMed | ChemPort |
  7. Melin, M. et al. Constitutional downregulation of SEMA5A expression in autism. Neuropsychobiology 54, 64–69 (2006) | Article | PubMed | ChemPort |
  8. Gaffrey, M. S. et al. Atypical participation of visual cortex during word processing in autism: an fMRI study of semantic decision. Neuropsychologia 45, 1672–1684 (2007) | Article | PubMed
  9. Hirota, H. et al. Williams syndrome deficits in visual spatial processing linked to GTF2IRD1 and GTF2I on chromosome 7q11.23. Genet. Med. 5, 311–321 (2003) | PubMed | ISI | ChemPort |
  10. Edelmann, L. et al. An atypical deletion of the Williams-Beuren syndrome interval implicates genes associated with defective visuospatial processing and autism. J. Med. Genet. 44, 136–143 (2007) | Article | PubMed | ChemPort |
  11. van Hagen, J. M. et al. Contribution of CYLN2 and GTF2IRD1 to neurological and cognitive symptoms in Williams Syndrome. Neurobiol. Dis. 26, 112–124 (2007) | Article | PubMed | ChemPort |
  12. Wang, K. et al. Common genetic variants on 5p14.1 associate with autism spectrum disorders. Nature 459, 528–533 (2009) | Article | PubMed | ChemPort |
  13. Zafeiriou, D. I., Ververi, A. & Vargiami, E. Childhood autism and associated comorbidities. Brain Dev. 29, 257–272 (2007) | Article | PubMed
  14. Szatmari, P. et al. Mapping autism risk loci using genetic linkage and chromosomal rearrangements. Nature Genet. 39, 319–328 (2007) | Article
  15. Bhangale, T. R., Rieder, M. J. & Nickerson, D. A. Estimating coverage and power for genetic association studies using near-complete variation data. Nature Genet. 40, 841–843 (2008) | Article
  16. Risch, N. J. Searching for genetic determinants in the new millennium. Nature 405, 847–856 (2000) | Article | PubMed | ISI | ChemPort |
  17. Arking, D. E. et al. A common genetic variant in the neurexin superfamily member CNTNAP2 increases familial risk of autism. Am. J. Hum. Genet. 82, 160–164 (2008) | Article | PubMed | ChemPort |
  18. Alarcón, M. et al. Linkage, association, and gene-expression analyses identify CNTNAP2 as an autism-susceptibility gene. Am. J. Hum. Genet. 82, 150–159 (2008) | Article | PubMed | ChemPort |
  19. Bakkaloglu, B. et al. Molecular cytogenetic analysis and resequencing of contactin associated protein-like 2 in autism spectrum disorders. Am. J. Hum. Genet. 82, 165–173 (2008) | Article | PubMed | ChemPort |
  20. Campbell, D. B. et al. Disruption of cerebral cortex MET signaling in autism spectrum disorder. Ann. Neurol. 62, 243–250 (2007) | Article | PubMed
  21. Campbell, D. B. et al. A genetic variant that disrupts MET transcription is associated with autism. Proc. Natl Acad. Sci. USA 103, 16834–16839 (2006) | Article | PubMed | ChemPort |
  22. Di Rienzo, A. Population genetics models of common diseases. Curr. Opin. Genet. Dev. 16, 630–636 (2006) | Article | PubMed | ISI | ChemPort |
  23. Abecasis, G. R., Cherny, S. S., Cookson, W. O. & Cardon, L. R. Merlin–rapid analysis of dense genetic maps using sparse gene flow trees. Nature Genet. 30, 97–101 (2002) | Article
  24. Purcell, S. et al. PLINK: a tool set for whole-genome association and population-based linkage analyses. Am. J. Hum. Genet. 81, 559–575 (2007) | Article | PubMed | ISI | ChemPort |
  25. Lord, C., Rutter, M. & Le Couteur, A. Autism Diagnostic Interview-Revised: a revised version of a diagnostic interview for caregivers of individuals with possible pervasive developmental disorders. J. Autism Dev. Disord. 24, 659–685 (1994) | Article | PubMed | ISI | ChemPort |
  26. Korn, J. M. et al. Integrated genotype calling and association analysis of SNPs, common copy number polymorphisms and rare CNVs. Nature Genet. 40, 1253–1260 (2008) | Article
  27. McCarroll, S. A. et al. Integrated detection and population-genetic analysis of SNPs and copy number variation. Nature Genet. 40, 1166–1174 (2008) | Article
  28. Hirschhorn, J. N. & Daly, M. J. Genome-wide association studies for common diseases and complex traits. Nature Rev. Genet. 6, 95–108 (2005) | Article
  29. Mitchell, A. A., Cutler, D. J. & Chakravarti, A. Undetected genotyping errors cause apparent overtransmission of common alleles in the transmission/disequilibrium test. Am. J. Hum. Genet. 72, 598–610 (2003) | Article | PubMed | ISI | ChemPort |
  30. The Wellcome Trust Case Control Consortium Genome-wide association study of 14,000 cases of seven common diseases and 3,000 shared controls. Nature 447, 661–678 (2007) | Article | PubMed | ChemPort |
  31. Gauthier, J. et al. Autism spectrum disorders associated with X chromosome markers in French-Canadian males. Mol. Psychiatry 11, 206–213 (2006) | Article | PubMed | ChemPort |
  32. Lord, C. et al. The autism diagnostic observation schedule-generic: a standard measure of social and communication deficits associated with the spectrum of autism. J. Autism Dev. Disord. 30, 205–223 (2000) | Article | PubMed | ISI | ChemPort |
  33. Berument, S. K., Rutter, M., Lord, C., Pickles, A. & Bailey, A. Autism screening questionnaire: diagnostic validity. Br. J. Psychiatry 175, 444–451 (1999) | Article | PubMed | ISI | ChemPort |
  34. Le Couteur, A. et al. Autism Diagnostic Interview: A standardized investigator-based instrument. J. Autism Dev. Disord. 19, 363–387 (1989) | Article | PubMed | ChemPort |
  35. Tyrer, P. J. Personality Disorders: Diagnosis, Management, and Course (Wright, 1988)
  36. Landa, R. et al. Social language use in parents of autistic individuals. Psychol. Med. 22, 245–254 (1992) | Article | PubMed | ChemPort |
  37. Mattila, M. L. et al. An epidemiological and diagnostic study of Asperger syndrome according to four sets of diagnostic criteria. J. Am. Acad. Child Adolesc. Psychiatry 46, 636–646 (2007) | Article | PubMed
  38. Wechsler, D. Wechsler Intelligence Scale for Children Third edn (The Psychological Corporation, 1991)
  39. World Health Organization. The ICD-10 Classification of Mental and Behavioural Disorders. Diagnostic Criteria for Research (WHO, 1993)
  40. Auranen, M. et al. A genomewide screen for autism-spectrum disorders: evidence for a major susceptibility locus on chromosome 3q25-27. Am. J. Hum. Genet. 71, 777–790 (2002) | Article | PubMed | ISI
  41. American Psychiatric Association. Diagnostic and Statistical Manual of Mental Disorders (DSM-IV) 4 edn (APA, 1994)
  42. Marshall, C. R. et al. Structural variation of chromosomes in autism spectrum disorder. Am. J. Hum. Genet. 82, 477–488 (2008) | Article | PubMed | ChemPort |
  43. Livak, K. J. & Schmittgen, T. D. Analysis of relative gene expression data using real-time quantitative PCR and the 2-DeltaDeltaCT method. Methods 25, 402–408 (2001) | Article | PubMed | ISI | ChemPort |
Top

Supplementary Information

Supplementary information accompanies this paper.

Top

Acknowledgements

We thank all of the families who have participated in and contributed to the public resources that we have used in these studies. The Broad Institute Center for Genotyping and Analysis is supported by grant U54 RR020278 from the National Center for Research Resources. The Gene Discovery Project of Johns Hopkins was funded by grants from the National Institutes of Mental Health (MH60007, MH081754) and the Simons Foundation. This study was funded in part through a grant from the Autism Consortium of Boston. Support for the Extreme Discordant Sib-Pair (EDSP) family sample was provided by the NLM Family foundation. Support for the Massachusetts General Hospital (MGH)–Finnish collaborative sample was provided by NARSAD. Support for the Homozygosity Mapping Collaborative for Autism (HMCA) came from NIMH (1R01 MH083565), the Nancy Lurie Marks (NLM) Family Foundation and the Simons Foundation. Eric M. Morrow is supported by the NIMH (1K23MH080954). Support for the Iranian family sample was provided by the Special Education Organization of Iran, under the Iranian Ministry of Education. Lauren A. Weiss was supported by a Ruth L. Kirschstein National Research Service Award and is currently supported by the International Mental Health Research Organization. The collection of data and biomaterials that participated in the National Institute of Mental Health (NIMH) Autism Genetics Initiative has been supported by National Institute of Health grants MH52708, MH39437, MH00219 and MH00980; National Health Medical Research Council grant 0034328; and by grants from the Scottish Rite, the Spunk Fund, Inc., the Rebecca and Solomon Baker Fund, the APEX Foundation, the National Alliance for Research in Schizophrenia and Affective Disorders (NARSAD), and the endowment fund of the Nancy Pritzker Laboratory (Stanford); and by gifts from the Autism Society of America, the Janet M. Grace Pervasive Developmental Disorders Fund, and families and friends of individuals with autism. The NIMH collection Principal Investigators and Co-Investigators were: Neil Risch, Richard M. Myers, Donna Spiker, Linda J. Lotspeich, Joachim F. Hallmayer, Helena C. Kraemer, Roland D. Ciaranello, Luigi Luca Cavalli-Sforza (Stanford University, Stanford); William M. McMahon and P. Brent Petersen (University of Utah, Salt Lake City). The Stanford team is indebted to the parent groups and clinician colleagues who referred families and extends their gratitude to the families with individuals with autism who were partners in this research. The collection data and biomaterials also come from the Autism Genetic Resource Exchange (AGRE) collection. This program has been supported by a National Institute of Health grant MH64547 and the Cure Autism Now Foundation. The AGRE collection Principal Investigator is Daniel H. Geschwind (UCLA). The Co-Principal Investigators include Stanley F. Nelson and Rita M. Cantor (UCLA), Christa Lese Martin (Univ. Chicago), T. Conrad Gilliam (Columbia). Co-Investigators include Maricela Alarcon (UCLA), Kenneth Lange (UCLA), Sarah J. Spence (UCLA), David H. Ledbetter (Emory) and Hank Juo (Columbia). Scientific oversight of the AGRE program is provided by a steering committee (Chair: Daniel H. Geschwind; Members: W. Ted Brown, Maja Bucan, Joseph D. Buxbaum, T. Conrad Gilliam, David Greenberg, David H. Ledbetter, Bruce Miller, Stanley F. Nelson, Jonathan Pevsner, Carol Sprouse, Gerard D. Schellenberg and Rudolph Tanzi). The Autism Genome Project (AGP) work was supported by the following grants: (1) The Hilibrand Foundation (Principal Investigator Joachim F. Hallmayer); (2) Autism Speaks (for the AGP); (3) grants from the National Institutes of Health (NIH) MH61009 (James S. Sutcliffe), MH55135 (Susan E. Folstein), MH55284 (Joseph Piven), HD055782 (Ellen M. Wijsman), NS042165 (Joachim F. Hallmayer); (4) Fundação para a Ciência e Tecnologia (POCTI/39636/ESP/2001) Fundação Calouste Gulbenkian (Astrid Vincente); (5) INSERM, Fondation de France, Fondation Orange, Fondation pour la Recherche Médicale (Catalina Betancur, Marion Leboyer), and the Swedish Science Council (Christopher Gillberg); (6) The Seaver Foundation (Joseph D. Buxbaum); (7) The Children’s Medical & Research Foundation (CMRF), Our Lady’s Children’s Hospital, Crumlin, Ireland (Sean Ennis); (8) The Medical Research Council (MRC) (Anthony P. Monaco, Anthony J. Bailey). Fresh-frozen brain tissue samples were obtained through the Autism Tissue Program and the Harvard Brain Bank.

Author Contributions L.A.W., D.E.A., M.J.D. and A. Chakravarti led design and execution of joint scan analyses and manuscript writing. Johns Hopkins University–NIMH genome scan team: D.E.A. and A. Chakravarti led study design and analysis of scan; C.W.B. and E.H.C. provided evaluation of phenotype data, phenotype definition from primary data and editing of the manuscript; K. West, A.O’C. and G.H. conducted primary and replication genotyping with allele calling; R.L.T. and A.B.W. performed expression analysis and editing of the manuscript. Autism Consortium–AGRE genome scan team: L.A.W., T.G. and M.J.D. performed data processing and analysis for the genome-wide association scan; S-C.C., E.M.H., E.M.M., R.S. and S.L.S. provided evaluation of phenotype data and phenotype definition from primary data; S.G., C. Gates, C. Sougnez and C. Stevens led the genotyping team; A.K., J.K., F.K., S.M., B.N. and S.P. performed and evaluated allele calling and advised the analysis; M.J.D., L.A.W., R.T., P.S., S.L.S., J. Gusella and D.A. designed and initiated the study and provided manuscript comments and edits. Replication teams: each replication team provided genotypes, phenotypes and analysis of top ranking SNPs from the combined genome-wide association scan and contributed comments during manuscript preparation.

Top

Competing interests statement

The authors declare  competing financial interests.

Top

The Gene Discovery Project of Johns Hopkins & the Autism Consortium

Top

Writing group

Mark J. Daly1,2 & Aravinda Chakravarti3
Top

Johns Hopkins University–NIMH genome scan team

Dan E. Arking3, Camille W. Brune4, Kristen West3, Ashley O’Connor3, Gina Hilton3, Rebecca L. Tomlinson5, Andrew B. West5, Edwin H. Cook Jr4 & Aravinda Chakravarti3
Top

Autism Consortium–AGRE genome scan team

Lauren A. Weiss1,2,75, Todd Green1,2, Shun-Chiao Chang1, Stacey Gabriel2, Casey Gates2, Ellen M. Hanson5, Andrew Kirby1,2, Joshua Korn1,2, Finny Kuruvilla1,2, Steven McCarroll1,2, Eric M. Morrow1,2,7,60,75, Benjamin Neale1,2, Shaun Purcell1,2, Roksana Sasanfar1,8, Carrie Sougnez2, Christine Stevens2, David Altshuler1,2, James Gusella1,2, Susan L. Santangelo1, Pamela Sklar1,2, Rudolph Tanzi1 & Mark J. Daly1,2
Top

Replication teams: Autism Genome Project Consortium (listed alphabetically)

Richard Anney28, Anthony J. Bailey9, Gillian Baird10, Agatino Battaglia56, Tom Berney12, Catalina Betancur13, Sven Bölte14, Patrick F. Bolton15, Jessica Brian16, Susan E. Bryson17, Joseph D. Buxbaum18, Ines Cabrito51, Guiqing Cai18, Rita M. Cantor19, Edwin H. Cook Jr5, Hilary Coon20, Judith Conroy26, Catarina Correia51, Christina Corsello21, Emily L. Crawford46, Michael L. Cuccaro22, Geraldine Dawson59, Maretha de Jonge24, Bernie Devlin25, Eftichia Duketis14, Sean Ennis26, Annette Estes23, Penny Farrar38, Eric Fombonne27, Christine M. Freitag14, Louise Gallagher28, Daniel H. Geschwind29, John Gilbert22, Michael Gill28, Christopher Gillberg53, Jeremy Goldberg30, Andrew Green26, Jonathan Green31, Stephen J. Guter4, Jonathan L. Haines32, Joachim F. Hallmayer33, Vanessa Hus21, Sabine M. Klauck34, Olena Korvatska55, Janine A. Lamb35, Magdalena Laskawiec9, Marion Leboyer54, Ann Le Couteur12, Bennett L. Leventhal4, Xiao-Qing Liu16,44, Catherine Lord21, Linda J. Lotspeich33, Elena Maestrini58, Tiago Magalhaes51, William Mahoney36, Carine Mantoulan37, Helen McConachie12, Christopher J. McDougle57, William M. McMahon20, Christian R. Marshall44, Judith Miller20, Nancy J. Minshew4, Anthony P. Monaco38, Jeff Munson23, John I. Nurnberger Jr57, Guiomar Oliveira52, Alistair Pagnamenta38, Katerina Papanikolaou39, Jeremy R. Parr9, Andrew D. Paterson16,44, Margaret A. Pericak-Vance22, Andrew Pickles40, Dalila Pinto44, Joseph Piven41, David J. Posey57, Annemarie Poustka34,76, Fritz Poustka14, Regina Regan26, Jennifer Reichert18, Katy Renshaw9, Wendy Roberts16, Bernadette Roge37, Michael L. Rutter42, Jeff Salt4, Gerard D. Schellenberg43, Stephen W. Scherer44, Val Sheffield45, James S. Sutcliffe46, Peter Szatmari30, Katherine Tansey28, Ann P. Thompson30, John Tsiantis39, Herman Van Engeland24, Astrid M. Vicente51, Veronica J. Vieland11, Fred Volkmar47, Simon Wallace9, Thomas H. Wassink48, Ellen M. Wijsman49, Kirsty Wing38, Kerstin Wittemeyer37, Brian L. Yaspan46 & Lonnie Zwaigenbaum50
Top

The Homozygosity Mapping Collaborative for Autism

Eric M. Morrow1,2,7,60,75, Seung-Yun Yoo2,7,60, Robert Sean Hill2,7,60, Nahit M. Mukaddes61, Soher Balkhy62, Generoso Gascon62,63, Samira Al-Saad65, Asif Hashmi64, Janice Ware6, Robert M. Joseph66, Elaine LeClair6, Jennifer N. Partlow7,60, Brenda Barry7,60 & Christopher A. Walsh2,7,60
Top

MGH Oulu study

David Pauls1, Irma Moilanen67, Hanna Ebeling67, Marja-Leena Mattila67, Sanna Kuusikko67, Katja Jussila67 & Jaakko Ignatius67
Top

MGH Iran study

Roksana Sasanfar1,8, Ala Tolouei8, Majid Ghadami8, Maryam Rostami68, Azam Hosseinipour8 & Maryam Valujerdi8
Top

MGH EDSP study

Susan L. Santangelo1, Kara Andresen1,69, Brian Winkloski1 & Stephen Haddad1
Top

Children’s Hospital Boston

Lou Kunkel7, Zak Kohane7, Tram Tran7, Sek Won Kong7, Stephanie Brewster O’Neil7, Ellen M. Hanson6, Rachel Hundley6, Ingrid Holm7, Heather Peters7, Elizabeth Baroni7, Aislyn Cangialose7, Lindsay Jackson7, Lisa Albers7, Ronald Becker7, Carolyn Bridgemohan7, Sandra Friedman7, Kerim Munir7, Ramzi Nazir7, Judith Palfrey7, Alison Schonwald7, Esau Simmons7 & Leonard A. Rappaport6
Top

Montreal

Julie Gauthier70, Laurent Mottron71, Ridha Joober27, Eric Fombonne27 & Guy Rouleau71
Top

Finland

Karola Rehnstrom72,73, Lennart von Wendt72,73 & Leena Peltonen72,73,74
Top

Online Methods

All samples used in this study arose from investigations approved by the individual and respective Institutional Review Boards in the USA and at international sites where relevant. Informed consent was obtained for all adult study participants; for children under age 18, both the consent of the parents or guardians and the assent of the child were obtained.

Primary study samples: AGRE samples

The Autism Genetic Resource Exchange (AGRE) curates a collection of DNA and phenotypic data from multiplex families with autism spectrum disorder (ASD) available for genetic research3. We genotyped individuals from 801 families, selecting those with at least one child meeting criteria for autism by the Autism Diagnostic Interview-Revised (ADI-R)25, whereas the second affected child had an AGRE classification of autism, broad spectrum (patterns of impairment along the spectrum of pervasive developmental disorders, including pervasive developmental disorder not otherwise specified (PDD-NOS) and Asperger’s syndrome) or not quite autism (NQA, individuals who are no more than one point away from meeting autism criteria on any or all of the social, communication, and/or behaviour domains and meet criteria for ‘age of onset’; or, individuals who meet criteria on all domains, but do not meet criteria for the ‘age of onset’). We excluded probands with widely discrepant classifications of affection status via the ADI-R and Autism Diagnostic Observation Schedule (ADOS) that could not be reconciled. We also excluded families with known chromosomal abnormalities (where karyotyping was available), and those with inconsistencies in genetic data (generating excess Mendelian segregation errors or showing genotyping failure on a test panel of 24 SNPs used to check gender and sample identity with the full array data). The self-reported race/ethnicity of these samples is 69% white, 12% Hispanic/Latino, 10% unknown, 5% mixed, 2.5% each Asian and African American, less than 1% native Hawaiian/Pacific Islander and American Indian/native Alaskan.

Primary study samples: NIMH samples

The NIMH Autism Genetics Initiative maintains a collection of DNA from multiplex and simplex families with ASD. We genotyped individuals from 341 nuclear families, 258 of which were independent of the AGRE data set, with at least one child meeting criteria for autism by the ADI-R, and a second child considered affected using the same criteria as described for the AGRE data set above. Similar exclusion criteria were used, including known chromosomal abnormalities and excess non-Mendelian inheritance. The self-reported race/ethnicity of these samples is 83% white, 4% Hispanic, 2% unknown, 7% mixed, 3% Asian and 1% African American.

Primary study samples: merged data set for primary screening

We used the Birdseed algorithm for genotype calling at both genotyping centres26, 27. As 324 individuals were genotyped at both centres, we performed a concordance check. One sample showed substantial differences between the two centres, but no excess of Mendelian errors, indicating that a sample mix-up occurred in which each centre genotyped a different sibling that was identified as the same sample. Excluding this sample, overall genotype concordance between the two centres was 99.72%.

Before merging data, we examined the distribution of chi-squared values and used a series of quality control (QC) filters designed to identify a robust set of SNPs. We discovered that filtering AGRE genotypes to 98% completeness and less than 10 Mendelian errors (MEs) was sufficient to remove SNPs that artificially inflated the chi-squared distribution for SNPs with MAF>0.05. For MAF<0.05, we observed much greater inflation (λ = 1.17), due entirely to a strong excess of SNPs with under-transmission of the minor allele (OR<1). Whereas the same filters yielded high-quality results for SNPs with over-transmission of the minor allele (λ = 1.04), we found that much stricter filtering was required for rarer SNPs with OR<1 (missing data <0.005). This is not unexpected based on a well-documented bias in the TDT: if missing data are preferentially biased against heterozygotes or rare homozygotes, significant, artificial over-transmission of the common allele is expected28, 29. To achieve comparable quality for the NIMH data set, we filtered on 96% completeness and fewer than 4 MEs. Our final QQ plot for the combined data set is shown in Supplementary Fig. 1 and has a λ 1.03, less than that observed in the Wellcome Trust Case Control Consortium paper for five of the seven phenotypes studied30. The combined data set, consisting of 1,031 families (856 with two parents) and a total of 1,553 affected offspring, was used for association testing.

For linkage analyses, the combined AGRE/NIMH data set was further merged with Illumina 550K genotype data generated at the Children’s Hospital of Philadelphia (CHOP) and available from AGRE, adding ~300 nuclear families (1,499 samples). We used the extensive overlap of samples between the AGRE/NIMH and the CHOP data sets (2,282 samples) to select an extremely high quality set of SNPs for linkage analysis. Specifically, we required SNPs to be on both the Affymetrix 500K/5.0 and Illumina 550K platforms, with >99.5% concordance across platforms. We further restricted SNPs to MAF>0.2, <1% missing data, Hardy–Weinberg P>0.01, and no more than 1 ME. This left ~36,000 SNPs of outstanding quality. For autosomal SNPs, we further pruned using PLINK to remove SNPs with r2>0.1, yielding 16,311 SNPs.

Replication samples: NIMH control samples

Controls obtained from the NIMH Genetics Repository were genotyped on the Affymetrix 500K platform at the Broad Institute Genetic Analysis Platform for another study6. Of these, 1,494 matched well with our sample, and were used as controls to compare with the cases and parents in our study.

Replication samples: Montreal samples

Subjects diagnosed with autism spectrum disorders with both of their parents were recruited from clinics specializing in the diagnosis of Pervasive Developmental Disorders (PDD), readaptation centres, and specialized schools in the Montreal and Quebec City regions, Canada, as described31. Subjects with ASD were diagnosed by child psychiatrists and psychologists expert in the evaluation of ASD. Evaluation based on the Diagnostic and Statistical Manual of Mental Disorders (DSM) criteria included the use of the ADI-R25 and the ADOS32. As an additional screening tool for the diagnosis of ASD, the Autism Screening Questionnaire, which is derived from the ADI-R, was completed33. Furthermore, all proband medical charts were reviewed by a child psychiatrist expert in PDD to confirm their diagnosis and exclude subjects with any co-morbid disorders. Exclusion criteria were: (1) an estimated mental age <18 months; (2) a diagnosis of Rett syndrome or childhood disintegrative disorder; and (3) evidence of any psychiatric and neurological conditions including: birth anoxia, rubella during pregnancy, fragile X syndrome, encephalitis, phenylketonuria, tuberous sclerosis, Tourette and West syndromes. Subjects with these conditions were excluded based on parental interview and chart review. However, participants with a co-occurring diagnosis of semantic-pragmatic disorder (owing to its large overlap with PDD), attention deficit hyperactivity disorder (seen in a large number of patients with ASD during development), and idiopathic epilepsy (related to the core syndrome of ASD) were eligible for the study.

Replication samples: Santangelo EDSP family samples

Families were ascertained for having one or more autistic children and at least one non-autistic child aged 16 or older for an extremely discordant sibling-pair linkage study. Recruitment took place in Massachusetts and surrounding states through contacts with parent support and patient advocacy groups, brochures, newsletters and the study website. Parents were interviewed about their children, and non-autistic children were interviewed about themselves. An informant/caregiver, usually the proband’s mother, was interviewed using the ADI-R to confirm the diagnosis of autism at age 4–5years25, 34. Families were included if the affected children met Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) criteria for autistic disorder and their non-autistic siblings (aged 16 and older) did not display any of the broader autism phenotype traits, which were assessed with the (M-PAS-R), the Pragmatic Language Scale (PLS), and the Friendship Interview35, 36. Probands were excluded if they had medical conditions associated with autism such as fragile X syndrome or gross CNS injury, or if they were under 4years of age, owing to the possible uncertainty in diagnosis at younger ages. Twenty-nine families met eligibility criteria for the study and comprised the final sample for analysis.

Replication samples: high functioning autism family samples

Families were included if their affected child had been previously diagnosed with Autism or Asperger’s syndrome, had a level of intellectual functioning above the range of mental retardation (that is, full scale, verbal and performance IQ>70), chronological age between 6 and 21years, and an absence of significant medical or neurological disorders (including fragile X syndrome and tuberous sclerosis). Families were ascertained and recruited through the Acute Residential Treatment (ART) programmes and outpatient child and adolescent services at McLean Hospital, as well as through associated hospitals and clinics. Brochures and a website were also used. Thirty-three families (133 participants) were enrolled in the study. Participation was voluntary.

Replication samples: MGH–Finnish collaborative samples

Altogether 58 individuals with a diagnosis of high functioning autism (HFA) or Asperger’s syndrome were recruited in Finland. Fifty-two children and adolescents aged 8–15years were identified from patient records at the Oulu University Hospital in 2003. These children and adolescents have been evaluated for HFA/Asperger’s syndrome at the Oulu University Hospital. In addition, six children (3 boys, 3 girls) 11years of age were recruited from an epidemiological study conducted in 2001 (ref. 37).

All participants had full-scale IQ scores greater than or equal to 80 measured with the Wechsler Intelligence Scale for Children—Third Revision38. Furthermore, none of the children subjects was diagnosed with other developmental disorders (for example, dysphasia, fragile X syndrome). Clinical diagnoses of HFA/Asperger’s syndrome were confirmed by administering the ADI-R25 and the ADOS32. Of the 58 participants with HFA/Asperger’s syndrome, 35 met the diagnostic criteria for Asperger’s syndrome and 21 met the diagnostic criteria for HFA according to ICD-10 (International Classification of Diseases v. 10) diagnostic criteria39. Two participants met diagnostic criteria for PDD-NOS; these participants were excluded owing to their manifesting different and less severe symptoms than our sample of children with HFA or Asperger’s syndrome.

Replication samples: Children’s Hospital Boston samples

Probands with a documented history of clinical diagnosis of ASD were recruited at Children’s Hospital Boston. To participate, they had to be over 24 months of age and have at least one biological parent or an affected sibling available. Subjects were excluded if they had an underlying metabolic disorder or any chronic systemic disease, an acquired developmental disability (for example, birth asphyxia, trauma-related injury, meningitis, etc.), or cerebral palsy. All participants provided informed consent and a phenotyping battery was performed including the ADOS, the ADI-R and other measures to assess cognitive status. Seventy-five per cent of subjects with a clinical diagnosis met strict research criteria for ASD on both ADI-R and ADOS. In addition, a complete family and medical history was obtained.

Replication samples: homozygosity mapping collaborative for autism (HMCA) samples

Families with cousin marriages and children affected by ASD with or without mental retardation were recruited by multiple collaborators in the HMCA. The patients from Istanbul were evaluated by a child psychiatrist (N. M. Mukaddes) trained in the ADOS and ADI-R, and who made diagnoses according to DSM-IV-TR criteria and the Childhood Autism Rating Scale (CARS). Patients from Kuwait were enrolled from the Kuwait Centre for Autism by S. Al-Saad. In Jeddah, Saudi Arabia, patients were evaluated by both a developmental paediatrician (S. Balkhy) and a paediatric neurologist (G. Gascon) and diagnoses were based on DSM-IV-TR criteria. In Lahore, Pakistan, a neurologist (A. Hashmi) with training in the ADOS and ADI-R diagnosed patients using DSM-IV-TR criteria. In most settings, patients were enrolled from tertiary clinical centres and these patients had standard of care neuromedical assessments, including physical examination, medical and neurological history, fragile X testing, and other genetic and metabolic testing when indicated. MRI was obtained for patients in whom a brain malformation was suspected or seizures were present. In addition, IQ scores (usually from the Stanford–Binet) and adaptive behaviour measures were obtained from the patients’ existing medical records. Secondary assessments were conducted on the most informative pedigrees by the Boston clinical team in collaboration with local multi-disciplinary teams. Clinical members of the Boston team included: developmental psychologists (J. Ware, E. LeClaire, R. M. Joseph), paediatric neurologists (G. H. Mochida, A. Poduri), a clinical geneticist (W.-H. Tan) and a neuropsychiatrist (E. M. Morrow). The secondary assessment battery was designed to obtain a comprehensive description of current and historical autism symptomatology, cognitive and adaptive functioning, and neurological and physical morphological status in the patient and pedigree. The secondary assessment included: neurological examination; genetic dysmorphology examination; the CARS; the Social Communication Questionnaire administered with probing on par with the ADI-R by ADI-R reliable examiners; the ADOS (usually module 1); the Vineland Adaptive Behaviour Scales, second edition (VABS-II); Kaufman Brief Intelligence Test, second edition (KBIT-II). ADOS assessments were videotaped and dysmorphology findings were photographed for archival purposes.

Replication samples: AGP samples

Individuals typically received at least two of three evaluations for autism symptoms: ADI-R, ADOS and clinical evaluation. Of the 1,679 affected individuals from 1,443 families, 966 met criteria for autism on the ADI-R and ADOS and most of these also had a clinical evaluation of autism; 160 affected individuals met criteria for autism on one of the two diagnostic instruments (ADI-R, ADOS) but were missing information on the other instrument; and, 553 individuals met criteria for spectrum disorder on one or both instruments. Affected individuals were recruited from both simplex and multiplex families, 71% of this sample being from multiplex families. Most of the families were of European ancestry (83%).

Replication samples: Finnish autism family samples

Families were recruited through university and central hospitals. Detailed clinical and medical examinations were performed by experienced child neurologists as described elsewhere40. Diagnoses were based on ICD-1039 and DSM-IV41 diagnostic nomenclatures. Families with known associated medical conditions or chromosomal abnormalities were excluded from the study. A total of 106 families included 400 individuals for whom genotype data was available. Of these, 111 had a diagnosis of infantile autism and 13 a diagnosis of Asperger’s syndrome. All families were Finnish, except for one family where the father was Turkish.

Replication samples: Iranian trio samples

Eligible participants in this study were Iranian families with at least one child affected with ASD, including cases of autistic disorder, Asperger’s syndrome and PDD-NOS. Eighty families (282 individuals) from Iran were ascertained and assessed. This sample was ascertained by screening and diagnostic testing of over 90,000 preschool children from Tehran in 2004. Diagnoses of children were made according to DSM-IV criteria via the ADI-R and the ADOS. Patients with abnormal karyotypes and dysmorphic features were excluded. Most of the families were father–mother–child trios but some had more than one affected child. All affected biological siblings were assessed with the same diagnostic tools. We have ascertained and assessed 80 families (282 individuals) from Iran.

Affymetrix genotyping

The AGRE samples were genotyped on Affymetrix 5.0 chips at the Genetic Analysis Platform of the Broad Institute, using standard protocols. The 5.0 chip was designed to genotype nearly 500,000 SNPs across the genome to enable genome-wide association studies26, 27. The NIMH controls were genotyped at the Broad Institute using the Affymetrix 500K Sty and Nsp chips, using a similar protocol6. The Autism Consortium and Montreal replication samples were also genotyped at the Broad Institute under the same conditions. The NIMH autism samples were genotyped at the Johns Hopkins Center for Complex Disease on the Affymetrix 500K (Nsp and Sty) and 5.0 platforms using similar standard protocols.

Genotype calling for the 5.0 arrays was performed by Birdseed26, 27 and for the 500K arrays was performed by BRLMM. As basic QC filters for the data generated at the Broad Institute, we required that genotyping was >95% complete for each individual, and that each family had fewer than 10,000 Mendelian inheritance errors across the genome. We also required that each SNP had >95% genotyping, fewer than 15 Mendelian errors, Hardy–Weinberg equilibrium P>10-10, and minor allele frequency greater than 1%. For the AGRE sample, this left 2,883 high-quality individuals genotyped for 399,147 SNPs with 99.6% average call rate. The basic filters for the data generated at Johns Hopkins were individual call rates >95% for 5.0 arrays and >90% for 500K arrays data, fewer than 5,000 Mendelian errors per family. Only monomorphic SNPs and those with greater than 50% missing data were dropped, for 498,216 SNPs. Our combined data set had nearly 365,000 SNPs passing QC.

Sequenom genotyping

SNPs were assayed using Sequenom technology for the AGP samples at three centres, namely Gulbenkian, Mt Sinai and Oxford: DNA from 1,629 families representing numerous recruiting sites was genotyped for 54 SNPs. SNPs with >3% missing data, namely rs4690464, rs10513025, and rs17088296, were excluded from analysis. The next step in our QC process was to remove families with≥4 Mendelian errors, out of 51 remaining loci, under the assumption that this indicated pedigree errors. Data from 110 families were removed owing to Mendelian errors. Thereafter, SNPs were removed if they showed excessive Mendelian errors (>16) in the remaining families. Using this criterion, two more SNPs, rs155437 and rs1925058, were removed from analysis. It was apparent that DNA quality varied by study site and could be responsible for concomitant genotype quality differences. Therefore, we also evaluated rate of missing genotypes per locus and study site. Our analyses showed that DNA from a few population samples showed excess missingness for two SNPs, rs4742408 and rs7869239, relative to the remaining population samples. Specifically three population samples showed more than 7% missing genotypes for rs4742408 and rs7869239 whereas the remaining population samples had about 1% or less missing genotypes. Therefore, for these loci we deleted genotypes only from the samples showing excess missingness. As a final QC step, we then evaluated missing genotypes for the remaining loci. If more than five loci were missing genotypes, the individual’s data was removed from analysis. By this criterion 76 additional families became uninformative for family-based association analysis, leaving 1,443 families for association analysis. The Finnish autism samples were genotyped in the Peltonen laboratory, and the Iranian trios were genotyped at the Broad Institute using very similar protocols. All samples were genotyped using aliquots from the same pooled primers and probes.

Copy number analysis

Because of previous reports of two large (>1 Mb), independent de novo deletions spanning this locus42, we assessed the region surrounding rs10513025 and the entire SEMA5A locus for copy number variation that could either explain or provide independent evidence of the importance of this region to autism using Birdsuite26 to analyse all Affymetrix 5.0 samples. Birdsuite genotypes previously annotated common copy number polymorphisms27 and in parallel searches for novel copy number variants (CNVs) using an HMM. Probe coverage in the region was good, with no 50-kb window having fewer than 10 probes and an average spacing between probes of 2.5kb, allowing very good sensitivity for CNVs greater than 25kb. We found no deletions or duplications near this SNP, nor any overlapping the gene SEMA5A. The closest CNS upstream and downstream of this SNP appeared to be a rare (~2–3% frequency, previously annotated CNP) 40-kb deletion from 288 kb from the 3′ end of SEMA5A, and a rare (~1% frequency, novel) 20-kb deletion 356kb upstream of the 5′ end of SEMA5A. Each of these appeared to be segregating polymorphisms, but fall far outside of the boundaries of SEMA5A and TAS2R1 and far beyond the linkage disequilibrium block containing rs10513025.

Expression analysis

Fresh-frozen brain tissue samples dissected from the cortex (Brodmann area 19) were obtained through the Autism Tissue Program (http://www.atpportal.org) from the Harvard Brain Bank and the NICHD Brain and Tissue Bank at the University of Maryland from 20 samples with a primary diagnosis of autism, and 10 controls. Total RNA was extracted using TRIzol reagent (Invitrogen) according to the manufacturer’s protocol. Complementary DNA (cDNA) was generated from 8μg of total RNA using the Superscript III First-Strand Synthesis kit (Invitrogen). cDNA was diluted 1:5 in 10mM Tris and 1μl of diluted cDNA was used per 10μl PCR reaction. Quantitative real-time PCR was performed on a Lightcycler 480 (Roche Applied Science) using 2× Taqman Gene Expression Master Mix and probes obtained from Applied Biosystems (ABI): SEMA5A (Hs01549381_m1), MAP2 (Hs01103234_g1), TBP (Hs00920497_m1), GAPDH (4333764F). For multiplex reactions, 0.5μl FAM-labelled SEMA5A probe and 0.5μl VIC-labelled MAP2 probe were used per 10μl reaction. The amount of SEMA5A relative to MAP2 was determined for each case using the ΔΔCt method43. Comparison of SEMA5A to TBP and GAPDH yielded similar results. Logistic regression was performed on autism status, adjusting for age at death, post-mortem interval, sex and SEMA5A expression, with a 1-sided P-value reported for the association of lower SEMA5A expression with autism status.

Determination of significance

To determine an appropriate experimental threshold for genome-wide significance, permutation was performed on this data set by gene-dropping, and genome-wide significance was estimated by taking the lowest P-value from each of 1,000 permuted data sets and using the 50th as a threshold for P<0.05 experiment-wide significance (P<2.5×10-7). To calculate an estimate of the effective number of tests (Teff), we used the following algorithm: (1) start with the most 5′ SNP on a chromosome (SNPi,j), where i = chromosome and j = SNP position, and calculate pairwise LD with all downstream SNPs within 1Mb (r2[SNP1,1×SNP1,n]). (2) For SNP1,1, Teff(1,1) = 1-max(r2[SNP1,1xSNP1,n]). (3) For chromosome i, Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com, where m = the total number of SNPs on a chromosome. (4) Unfortunately we are unable to provide accessible alternative text for this. If you require assistance to access this image, or to obtain a text description, please contact npg@nature.com. Because this algorithm only accounts for pair-wise LD, it provides a conservative estimate of the number of effective tests.

MORE ARTICLES LIKE THIS

These links to content published by NPG are automatically generated.


Readers' Comments

If you find something abusive or inappropriate or which does not otherwise comply with our Terms and Conditions or Community Guidelines, please select the relevant 'Report this comment' link.

There are currently no comments.

Add your own comment

This is a public forum. Please keep to our Community Guidelines. You can be controversial, but please don't get personal or offensive and do keep it brief. Remember our threads are for feedback and discussion - not for publishing papers, press releases or advertisements.

You need to be registered with Nature and agree to our Community Guidelines to leave a comment. Please log in or register as a new user. You will be re-directed back to this page.