Human Molecular Genetics Advance Access originally published online on December 1, 2008
Human Molecular Genetics 2009 18(4):785-796; doi:10.1093/hmg/ddn402
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GRM7 variants confer susceptibility to age-related hearing impairment
1 House Ear Institute, Gonda Research Center for Cell and Molecular Biology, Los Angeles, CA, USA 2 Department of Medical Genetics, University of Antwerp, Antwerp, Belgium 3 Department of Otorhinolaryngology, University Hospital of Antwerp, Antwerp, Belgium 4 Neurogenomics Division, The Translational Genomics Research Institute, Phoenix, AZ, USA 5 Department of Otorhinolaryngology, University of Tampere, Tampere, Finland 6 Department of Otorhinolaryngology, Radboud University Nijmegen Medical Centre, Nijmegen, the Netherlands 7 Department of Otorhinolaryngology, University Hospital of Ghent, Ghent, Belgium 8 Welsh Hearing Institute, Cardiff University, Cardiff, UK 9 Department of Oto-surgery, University Hospital Padova, Padova, Italy 10 Department of Otorhinolaryngology, University of Tübingen, Tübingen, Germany 11 Department of Audiology, Bispebjerg Hospital, Copenhagen, Denmark 12 Department of Otorhinolaryngology, University of Oulu, Oulu, Finland
* To whom correspondence should be addressed. House Ear Clinic, Suite 111, 2100 W. 3rd Street, Los Angeles, CA 90057. Tel: +1 213-273-8078; Fax: +1 213-273-8088; Email: rfriedman{at}hei.org
Received October 7, 2008; Accepted November 20, 2008
Age-related hearing impairment (ARHI), or presbycusis, is the most prevalent sensory impairment in the elderly. ARHI is a complex disease caused by an interaction between environmental and genetic factors. Here we describe the results of the first whole genome association study for ARHI. The study was performed using 846 cases and 846 controls selected from 3434 individuals collected by eight centers in six European countries. DNA pools for cases and controls were allelotyped on the Affymetrix 500K GeneChip® for each center separately. The 252 top-ranked single nucleotide polymorphisms (SNPs) identified in a non-Finnish European sample group (1332 samples) and the 177 top-ranked SNPs from a Finnish sample group (360 samples) were confirmed using individual genotyping. Subsequently, the 23 most interesting SNPs were individually genotyped in an independent European replication group (138 samples). This resulted in the identification of a highly significant and replicated SNP located in GRM7, the gene encoding metabotropic glutamate receptor type 7. Also in the Finnish sample group, two GRM7 SNPs were significant, albeit in a different region of the gene. As the Finnish are genetically distinct from the rest of the European population, this may be due to allelic heterogeneity. We performed histochemical studies in human and mouse and showed that mGluR7 is expressed in hair cells and in spiral ganglion cells of the inner ear. Together these data indicate that common alleles of GRM7 contribute to an individual's risk of developing ARHI, possibly through a mechanism of altered susceptibility to glutamate excitotoxicity.
The authors wish it to be known that, in their opinion, the first three authors should be regarded as joint First Authors.