[Tonal audiometry of GJB2 235delC single heterozygous mutation carriers].

OBJECTIVE: To analyze GJB2 235delC monoallelic mutation carrier individuals and test the possible presence and incidence of audiometric abnormalities among 30-60 years old carriers of the 235delC mutations. METHODS: A total of 32 unrelated subjects with nonsyndromic hearing loss were screened for the 235delC mutation. Tonal audiometric analysis was performed on the 235delC mutation carrier group and on a non-carrier control group. RESULTS: Audiometric evaluations in the control group showed the presence of thresholds within normal limits at all frequencies, while carriers of the 235delC mutation presented with decreased hearing at 1000 Hz and 2000 Hz (age 40-49 years and 50-59 years), and 4000 and 8000 Hz (age 30-59 years), P < 0.05. The hearing loss of carriers gradually increased with age. CONCLUSIONS: GJB2 235delC heterozygous carriers may be a risk group for high-frequency hearing loss. Hearing thresholds may deteriorate in the intermediate frequencies over the age of 40.

[Sequencing analysis of whole SLC26A4 gene in severe to profound sensorineural hearing loss patients with IVS7-2A to G mutation of the gene].

OBJECTIVE: To investigate the whole sequence of the SLC26A4 gene in moderate to profound sensorineural hearing loss (SNHL) patients with IVS7-2A to G mutation of the gene in China. METHODS: Whole SLC26A4 gene sequence was analyzed by direct sequencing in 80 SLC26A4 gene IVS7-2A to G mutation carriers for the occurrence of a second mutation in the gene. RESULTS: Forty-seven out of the 80 patients were found to have a second heterozygous mutation, whereas a single IVS7-2A to G mutation could be responsible for SNHL in the remaining 33 patients. Three novel mutations, 5+ 2T to A, 14-2A to G and 1825del G, were identified. The five most common mutations include H723R (20%), T410M(5%), C.1705+ 5G to A (15+ 5G to A)(5%), L676Q(5%), and N392Y (3.75%). Exon 17 harbored the most types of compound heterozygosity with the IVS7-2A to G mutation. CONCLUSION: A Chinese specific SLC26A4 diversity was found, and comparable SLC26A4 contributing to deafness. This study suggested that if a heterozygous SLC26A4 mutation is found in a patient with deafness, other exons of the SLC26A4 gene should be analyzed. Furthermore, double heterozygosity of the SLC26A4 gene may also account for some of the disease phenotype.

[GJB2 235delC single allelic mutation modulates the phenotype associated with the mitochondrial A1555G mutation].

OBJECTIVE: To investigate a non-syndromic deafness family in which potential interaction between the GJB2 gene and a mitochondrial gene appeared to be the cause of hearing impairment. METHODS: Audiological examination was performed by pure-tone audiometry (PTA). Blood samples from 8 members of the pedigree were obtained. DNA was extracted from the leukocytes. The coding region of the GJB2 gene and mitochondrial DNA target fragments were amplified by polymerase chain reaction (PCR). The PCR products were analyzed by sequencing. RESULTS: Direct sequencing showed that the proband had both a heterozygous mutation of 235delC in the GJB2 gene and a mitochondrial 1555 A to G mutation. The proband had profound hearing loss. The maternal relatives had sensorineural hearing loss in the higher frequencies or no hearing loss. CONCLUSION: The GJB2 mutations may be an aggravating factor in the phenotypic expression of the non-syndromic hearing loss associated with the A1555G mitochondrial mutation.