V37I connexin 26 allele in patients with sensorineural hearing loss: evidence of its pathogenicity

Sensorineural hearing loss (SNHL) is the most common inherited sensory disorder, reported in 1-3 of every 1,000 births. It has been estimated that 50% of all cases of prelingual SNHL are genetically determined. There is tremendous genetic heterogeneity, with multiple dominant and recessive loci. Mutations of the gap junction beta-2 gene (GJB2) emerge as a leading cause of autosomal recessive non-syndromic SNHL. Over 90 sequence alterations have been reported, the pathogenicity of some of them being unknown or unclear. The status of the V37I allele of connexin 26 (GJB2 amino acid product) with regards to its association with SNHL has been controversial. This study examines the pathogenicity of V37I by comparing the frequency of this allele in 40 patients with SNHL of Chinese and Caucasian descent with the frequency of the allele in 100 anonymized, ethnically matched controls. The V37I allele was identified in 43.75 and 11.5% of the patient and control alleles of Chinese ethnicity, respectively, but was not found in either Caucasian cohort. We also compiled the audiograms of 15 individuals with SNHL homozygous for the V37I allele, and showed that these individuals present with a mild to moderate SNHL. These results indicate that (1) the V37I allele is common in individuals of Chinese descent but rarely present in individuals of Caucasian decent; and (2) the V37I allele is pathogenic, but produces milder hearing loss compared to nonsense mutations of connexin 26 such as the 35delG mutation.