Investigation of the DAOA/G30 locus in panic disorder

SIR—Recently, Hamilton et al1 performed a genome-wide scan in 60 multiplex pedigrees with a ‘panic disorder syndrome’ and found the most convincing linkage evidence on 13q32–q33. This chromosomal region has received strong attention in the study of schizophrenia and bipolar affective disorder (BPAD), since genetic variants within or near to the overlapping genes D-amino-acid oxidase activator (DAOA) and G30 located on 13q33 were associated with both schizophrenia and BPAD.2, 3, 4 In this study, we hypothesized that the DAOA/G30 locus might also confer risk for the development of panic disorder (PD). Several lines of evidence support this hypothesis: firstly, DAOA/G30 is located within the linkage peak for panic disorder syndrome observed by Hamilton et al.1 Secondly, results of several clinical and epidemiological studies suggest a shared etiologic background between PD and schizophrenia, for example, Bayle et al,5 as well as between PD and BPAD, for example, MacKinnon et al.6 Thirdly, recent findings suggest the involvement of DAOA in the glutamatergic signaling pathway,2 a pathway that has been implicated in anxiogenesis.

We analyzed SNPs at the DAOA/G30 locus in a sample consisting of 152 patients with PD and 208 controls of German descent. Patients were diagnosed according to DSM-IIIR and DSM-IV on the basis of structured clinical interviews (SADS-LA7 and CIDI8) and/or a review of medical records. The control individuals were anonymous blood donors, who had been recruited independently from the controls used in our previous association study of schizophrenia and BPAD.4 We focused on SNPs rs2391191 (M15), rs3918342 (M23), and rs421292 (M24), as these had shown the strongest association in our previous work.4 Additionally, we typed two flanking SNPs, rs778293 (M22) and rs3916972 (M25), covering this chromosomal region. Genotyping was carried out using the MassARRAY system (Sequenom, San Diego, USA) according to the genotyping method described by Ding and Cantor,9 with minor modifications (see Supplementary table). We performed both single-marker and haplotype analyses with the program COCAPHASE 2.40.10

Of the five variants at the DAOA/G30 locus typed, three SNPs (rs778293, rs3918342, and rs1421292) proved to be in significant LD with PD (Table 1), with the strongest evidence being observed for rs1421292 (P=0.031, OR 1.39). At the genotypic level, significant association was found between PD patients and rs1421292 under a dominant model (P=0.024, OR 2.12, Table 1). Given that a Bonferroni correction to adjust for multiple testing of loci would be overly conservative, and given the high levels of LD of these closely related markers, we used a permutation procedure instead. Our best P-value in the allelewise analysis was 0.031. In our simulation, a P-value of 0.031 or smaller would be seen by chance alone in 1129 times out of 10 000 replicates, yielding an empirical P-value of 0.113. In a subsequent step, we performed haplotype analysis (data not shown) comprising SNPs rs778293, rs3918342, and rs1421292, which were associated with disease in the single-locus analysis. The three-marker haplotype T–T–A was significantly less frequent in patients with PD (40 vs 48% in controls, P=0.030), and the haplotype C–C–T was more frequent in PD patients (42 vs 35% in controls, P=0.072). Although far from being significant (P-values >0.1), it is interesting to note that the allelic and haplotypic associations seem to be stronger in PD than in schizophrenia and BPAD. For example, the same alleles of rs3918342 and rs1421292 previously shown to be associated with schizophrenia and BPAD4 were even more frequent in patients with PD (rs3918342 allele C: 53% in schizophrenia and BPAD,4 57% in PD; rs1421292 allele T: 56 and 55% in schizophrenia and BPAD,4 respectively, 60% in PD).

Table 1 Statistical evaluation of allele and genotype frequencies for SNPs at the DAOA/G30 locus

Despite the fact that the observed single-marker associations do not withstand a stringent and robust adjustment for multiple testing at a nominal level of significance, our results suggest that variability at the DAOA/G30 locus may be involved in the etiology of PD. Since we have previously observed the same alleles and haplotypes to be associated with disease in our study on BPAD and schizophrenia, we believe that our findings are of potential interest for the psychiatric genetic community and may give a new perspective on conventional diagnostic categories.

References

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Correspondence to J Schumacher.

Additional information

Supplementary Information accompanies the paper on Molecular Psychiatry website (http://www.nature.com/mp).

Supplementary information

Supplementary table

Genotyping primers

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