Genotypic and phenotypic correlations of DFNB1-related hearing impairment in the Midwestern United States

Objective: To determine the genotypic and phenotypic correlations of hearing impairment (HI) in a mid-western US population related to autosomal recessive nonsyndromic hearing loss locus 1 (DFNB1). Design: A retrospective review. Setting: Tertiary care children's hospital. Patients: A total of 160 consecutive children diagnosed with idiopathic sensorineural hearing loss. Main Outcome Measures: GJB2 genotype and audiometric phenotype. Results: The 1 prevalence of subjects with HI having biallelic GJB2-related mutationsmas 15.3% (24/157). Of these 24 patients, 9 (38%) were homozygous 35delG, 6 (25%) had other biallelic nonsense mutations, and 9 (38%) had a missense mutation of at least 1 allele. The allelic prevalence of 35delG was 8.6% (27/314) in the study population and 48%(23/48). in the DFNB1 group. The M34T allele mutation was next most prevalent at 2.2% (7/314) in the study population and 10% (5/48) in the DFNB1 group. Severe to profound HI occurred in 59% of DFNB1 subjects. Genotypes with biallelic nonsense mutations had a high risk of severe to profound HI (88%). DFNB1-related HI was usually bilateral, symmetric, non-progressive, and had flat audiograms. However, asymmetric Hi (22%), sloping audiograms (26%), and even borderline-normal hearing in 1 ear was observed, and these were associated with the presence of at least 1 missense mutation. Two novel mutations, K15T and L90V, were identified. A subject presenting to our clinic with severe to profound HI had a 40% risk of biallelic GJB2 mutation. Conclusions: Our population represents a consecutively enrolled clinic population with sensorineural hearing loss. In our DFNB1-related HI cohort, the 35delG mutation and severe to profound HI rates were lower than previously reported. Our missense mutation and M34T allelic prevalence rates were higher than expected and were associated with a less severe hearing loss. The presence of biallelic nonsense mutations was associated with severe to profound hearing loss in nearly 90% of cases. Mild asymmetric HI and sloping audiograms were more often associated with missense mutations.