Objective: To investigate the etiology of patients with severe to profound hearing loss and to identify the ratio of hereditary hearing loss in Chifeng area in Northern China.
Methods: DNA were extracted from peripheral blood of 134 deaf patients from Chifeng special educational school and 100 normal hearing controls in Northern China. Audiology examinations showed that all patients had severe to profound bilateral sensorineural hearing impairment. Sequence analysis of the whole coding areas of GJB2, GJB3, GJB6, SLC26A4, mtDNA12SrRNA and mtDNAtRNASer(UCN) were performed. Individuals carrying SLC26A4 mutation were given further temporal bone CT scan.
Results: The ratio of hearing loss related to genetic factors in this population was 60.45% (81/134). About 33.58% (45/134) of the patients were given accurate genetic diagnosis. GJB2 mutations were responsible for approximately 17.16% of the cases in ChiFeng area. By screening SLC26A4 followed by temporal bone CT scan, we diagnosed 20 cases of enlarged vestibular aqueduct (EVA) and/or other inner ear malformation. SLC26A4 mutations account for about 14.93% of the cases. The aminoglycoside-related mtDNA 1555A>G mutation accounted for 0.76% of the cases in Chifeng area. In addition, another 13.43% (18/134) of the cases carried heterozygous GJB2 mutation and their hearing loss may be related to GJB2. 6.72% (9/134) of the cases carried heterozygous SLC26A4 mutation who were not found EVA by temporal bone CT or not took CT examination for some reasons. However, their hearing loss may also be SLC26A4-related. About 2.24% (3/134) of the cases carried mtDNA 12SrRNA 1095 T>C which may also be an aminoglycoside-related mutation and very likely be the cause of hearing loss. GJB3 might participate in the pathomechanism of hearing loss in 1.49% (2/134) of the patients. GJB6 mutation was not detected in this population.
Conclusions: The ratio of hearing loss related to genetic factors in the sample drawing population from Chifeng was 60.45% (81 cases). GJB2 is the most common gene and SLC26A4 is the second common gene next to GJB2 that cause deafness in this area.