Otosclerosis is a common form of progressive hearing loss, characterized by abnormal bone remodeling in the otic capsule. The etiology of the disease is largely unknown, and both environmental and genetic factors have been implicated. To identify genetic factors involved in otosclerosis, we used a case-control discovery group to complete a genome-wide association (GWA) study with 555,000 single-nucleotide polymorphisms (SNPs), utilizing pooled DNA samples. By individual genotyping of the top 250 SNPs in a stepwise strategy, we were able to identify two highly associated SNPs that replicated in two additional independent populations. We then genotyped 79 tagSNPs to fine map the two genomic regions defined by the associated SNPs. The region with the strongest association signal, p(combined) = 6.23 x 10(-10), is on chromosome 7q22.1 and spans intron 1 to intron 4 of reelin (RELN), a gene known for its role in neuronal migration. Evidence for allelic heterogeneity was found in this region. Consistent with the GWA data, expression of RELN was confirmed in the inner ear and in stapes footplate specimens. In conclusion, we provide evidence that implicates RELN in the pathogenesis of otosclerosis.

Otosclerosis is a progressive hearing loss characterized by an abnormal bone homeostasis of the otic capsule that leads to stapes fixation. Although its etiology remains unknown, otosclerosis can be considered a complex disease. Transforming growth factor-beta 1 (TGF-beta1) was chosen for a case-control association study, because of several non-genetic indications of involvement in otosclerosis. Single nucleotide polymorphism (SNP) analysis in a large Belgian-Dutch sample set gave significant results (P = 0.0044) for an amino acid changing SNP, T263I. Analysis of an independent French population replicated this association with SNP T263I (P = 0.00019). The results remained significant after multiple testing correction in both populations. Haplotype analysis and the results of an independent effect test using the weighted haplotype (WHAP) computer program in both populations were both compatible with SNP T263I being the only causal variant. The variant I263 is under-represented in otosclerosis patients and hence protective against the disease. Combining the data of both case-control groups for SNP T263I with a Mantel-Haenszel estimate of common odds ratios gave a very significant result (P = 9.2 x 10(-6)). Functional analysis of SNP T263I with a luciferase reporter assay showed that the protective variant I263 of TGF-beta1 is more active than the WT variant T263 (P = 1.6 x 10(-6)). On the basis of very low P-values, replication in an independent population and a functional effect of the protective variant, we conclude that TGF-beta1 influences the susceptibility for otosclerosis, and that the I263 variant is protective against the disease.

We studied the role of polymorphisms in 13 candidate genes on the risk of otosclerosis in two large independent case-control sets. We found significant association in both populations with BMP2 and BMP4, implicating these two genes in the pathogenesis of this disease.Introduction: Otosclerosis is a progressive disorder of the human temporal bone that leads to conductive hearing loss and in some cases sensorineural or mixed hearing loss. In a few families, it segregates as a monogenic disease with reduced penetrance, but in most patients, otosclerosis is more appropriately considered a complex disorder influenced by genetic and environmental factors. Materials and Methods: To identify major genetic factors in otosclerosis, we used a candidate gene approach to study two large independent case-control sets of Belgian-Dutch and French origin. Tag single nucleotide polymorphisms (SNPs) in 13 candidate susceptibility genes were studied in a stepwise strategy. Results: Two SNPs were identified that showed the same significant effect in both populations. The first SNP, rs3178250, is located in the 3Ј untranslated region of BMP2. Individuals homozygote for the C allele are protected against otosclerosis (combined populations: p ‫ס‬ 2.2 × 10

Otosclerosis is a common form of hearing loss characterized by abnormal bone remodeling in the otic capsule. It is considered a complex disease caused by both genetic and environmental factors. In a previous study, we identified a region on chr7q22.1 located in the RELN gene that is associated with otosclerosis in Belgian-Dutch and French populations. Evidence for allelic heterogeneity was found in this chromosomal region in the form of two independent signals. To confirm this finding, we have completed a replication study that includes four additional populations from Europe (1,141 total samples). Several SNPs in this region replicated in these populations separately. While the power to detect significant association in each population is small, when all four populations are combined, six of seven SNPs replicate and show an effect in the same direction as in the previous populations. We also confirmed the presence of allelic heterogeneity in this region. These data further implicate RELN in the pathogenesis of otosclerosis. Functional research is warranted to determine the pathways through which RELN acts in the pathogenesis of otosclerosis.

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SummaryOtosclerosis is one of the most common forms of hearing loss in the European population. We have identified a SNP in the TGFB1 (transforming growth factor beta 1) gene that is associated with susceptibility to otosclerosis. The protective allele of this variant, with isoleucine at position 263 of the protein, is more biologically active than the risk allele, which has a threonine in this position. Because recent studies have shown that not only common, but also rare variants can be involved in complex diseases, we performed DNA sequence analysis of the exons and intron-exon boundaries of TGFB1 in 755 otosclerosis patients and 877 control samples. We found 3 different nonsynonymous variants (E29, A29 and I241) in four otosclerosis patients, but no such changes were found in controls. In silico analysis shows that these variations could influence TGF-β1 function and activity. Taking into account that most rare missense alleles are thought to have a biological effect, the data suggest that multiple rare amino acid changing variants in TGF-β1 may contribute to susceptibility to otosclerosis.

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Otosclerosis is a common disorder of the otic capsule resulting in hearing impairment in 0.3-0.4% of the Caucasian population. The aetiology of the disease remains unclear. In most cases, otosclerosis can be considered as a complex disease. In some cases, the disease is inherited as an autosomal dominant trait, sometimes with reduced penetrance. To date, seven autosomal dominant loci have been reported, but none of the disease-causing genes has been identified. In this study, we present the results of a genome-wide linkage analysis in a large Tunisian family segregating autosomal dominant otosclerosis. Linkage analysis localised the responsible gene to chromosome 9p13.1-9q21.11 with a maximal LOD score of 4.13, and this locus was named OTSC8. Using newly generated short tandem repeat polymorphism markers, we mapped this new otosclerosis locus to a 34.16 Mb interval between the markers D9S970 and D9S1799. This region comprises the pericentromeric region on both arms of chromosome 9, a highly complex region containing many duplicated sequences.