1. ¹Department of Medical Genetics, University of Antwerp (UA), Antwerp, Belgium
2. ²Translational Genomics Research Institute, Phoenix, AZ, USA
3. ³Institute of Physiology and Pathology of Hearing, Warsaw, Poland
4. ⁴Department of Diabetology, Newborn Pathology and Birth Defects, Medical University of Warsaw, Warsaw, Poland
5. ⁵Department of Medical Genetics, Medical University of Warsaw, Warsaw, Poland
6. ⁶Medical Genetics, UO Audiology, Fondazione IRCCS, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milan, Italy
7. ⁷Medical Genetics Laboratory, Molecular Genetics, Fondazione IRCCS, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milan, Italy
8. ⁸ENT and Ophthalmology Department, University of Milan, UO Audiology, Fondazione IRCCS, Ospedale Maggiore Policlinico, Mangiagalli e Regina Elena, Milan, Italy
9. ⁹Department of Pediatrics, Rare Disease Center, University of Padua, Padua, Italy
10. ¹⁰Pediatric Audiology Unit, Department of Otolaryngology and Otosurgery, University Hospital of Padova, Padua, Italy
11. ¹¹Department of Human Genetics, Virginia USA Commonwealth University School of Medicine, Richmond, VA, USA
12. ¹²Department of Biology, Gallaudet University, Washington, DC, USA
13. ¹³Department of Child Neurology DNA laboratory, 2nd School of Medicine, Charles University Prague, Prague, Czech Republic
14. ¹⁴Department of Child ENT, 2nd School of Medicine, Charles University Prague and University Hospital Motol, Prague, Czech Republic
15. ¹⁵Service de Biochimie et de Biologie Moléculaire, Hôpital d'Enfants Armand-Trousseau, AP-HP, Paris, France
16. ¹⁶Unité de Génétique Médicale, Hôpital d'Enfants Armand-Trousseau, AP-HP, Paris, France
17. ¹⁷Service d'ORL et de Chirurgie Cervico-Faciale, Hôpital d'Enfants Armand-Trousseau, AP-HP and UPMC Paris 06, Paris, France
18. ¹⁸Department of Otolaryngology and Interdepartmental PhD Program in Genetics, University of Iowa, Iowa city, IA, USA
19. ¹⁹Division of Clinical Genetics, Innsbruck Medical University, Innsbruck, Austria
20. ²⁰Clinical Department of Hearing, Voice and Speech Disorders, Innsbruck Medical University, Innsbruck, Austria
21. ²¹Audiology and ENT Department, University Hospital, Ferrara, Italy
22. ²²Department of Otolaryngology, Medical and Health Science Center, University of Debrecen, Debrecen, Hungary
23. ²³Unidad de Genética Molecular, Hospital Ramón y Cajal and Centro de Investigación, Biomédica en Red de Enfermedades Raras (CIBERER), Madrid, Spain
24. ²⁴Department of Genetics, Institute of Child Health, 'Aghia Sophia' Children's Hospital, Athens, Greece
25. ²⁵Department of Psychoacoustics-Neurootology, AHEPA Hospital, 3rd Psychiatric Clinic, Aristotle University of Thessaloniki, Thessaloniki, Greece
26. ²⁶Division of Pediatric Molecular Genetics, Ankara University School of Medicine, Ankara, Turkey
27. ²⁷Department of Otolaryngology – Head&Neck Surgery, Eskisehir Osmangazi University, Eskisehir, Turkey
28. ²⁸Department of Audiology and Laryngology, Institute of Mother and Child, Warsaw, Poland
29. ²⁹Department of Medical Genetics, Institute of Mother and Child, Warsaw, Poland
30. ³⁰Department of Otorhinolaryngology, University Hospital Antwerp (UZA), University of Antwerp (UA), Antwerp, Belgium
31. ³¹Laboratoire de Génétique Moléculaire, CHU Montpellier, Montpellier, France
32. ³²ENT department, Sensory Genetic Disease National reference centre, Hôpital de Montpellier, Montpellier, France
33. ³³Laboratoire de Génétique Humaine, Développement et Cancer, Université Victor Segalen Bordeaux 2, Bordeaux, France
34. ³⁴Laboratoire de Génétique Moléculaire, CHU Pellegrin, Bordeaux, France
35. ³⁵Faculty of Science, Centre for Biodiversity Functional and Integrative Genomics (BioFIG), University of Lisbon, Lisbon, Portugal
36. ³⁶Department of Otolaryngology, University of Miami, Miami, FL, USA
37. ³⁷The Eargroup, Antwerp, Belgium
38. ³⁸Medical Genetics Laboratory, Kennedy Center, Glostrup, Denmark
39. ³⁹Department of Audiology, Bispebjerg Hospital, Copenhagen, Denmark
40. ⁴⁰Department of Otorhinolaryngology, Medical University of Vienna, Vienna, Austria
41. ⁴¹Klinische Audiologie, Universitair Ziekenhuis Gent, Gent, Belgium
42. ⁴²Department of Human Genetics, University Wuerzburg, Wuerzburg, Germany

Correspondence: Professor G Van Camp, Department of Medical Genetics, University of Antwerp-campus Drie Eiken, Universiteitsplein 1, B-2610 Antwerp, Belgium. Tel: +32 3 820 27 25; Fax: +32 3 820 25 66; E-mail: guy.vancamp@ua.ac.be

Received 23 June 2008; Revised 10 September 2008; Accepted 23 September 2008; Published online 5 November 2008.

Abstract

Hereditary hearing loss (HL) is a very heterogeneous trait, with 46 gene identifications for non-syndromic HL. Mutations in GJB2 cause up to half of all cases of severe-to-profound congenital autosomal recessive non-syndromic HL, with 35delG being the most frequent mutation in Caucasians. Although a genotype–phenotype correlation has been established for most GJB2 genotypes, the HL of 35delG homozygous patients is mild to profound. We hypothesise that this phenotypic variability is at least partly caused by the influence of modifier genes. By performing a whole-genome association (WGA) study on 35delG homozygotes, we sought to identify modifier genes. The association study was performed by comparing the genotypes of mild/moderate cases and profound cases. The first analysis included a pooling-based WGA study of a first set of 255 samples by using both the Illumina 550K and Affymetrix 500K chips. This analysis resulted in a ranking of all analysed single-nucleotide polymorphisms (SNPs) according to their P-values. The top 250 most significantly associated SNPs were genotyped individually in the same sample set. All 192 SNPs that still had significant P-values were genotyped in a second independent set of 297 samples for replication. The significant P-values were replicated in nine SNPs, with combined P-values between 3 10^-3 and 1 10^-4. This study suggests that the phenotypic variability in 35delG homozygous patients cannot be explained by the effect of one major modifier gene. Significantly associated SNPs may reflect a small modifying effect on the phenotype. Increasing the power of the study will be of greatest importance to confirm these results.