Molecular Genetic Characterization Of Two Chinese Pedigrees With Aminoglycoside-induced And Non-syndromic Hearing Loss

Objective:To explore the molecular genetic characterization of two Chinese families withaminoglycoside-induced and nonsyndromic sensorineural hearing loss.Methods:Blood samples were obtained from 7 maternal members and 1 married-in spouseof the two Chinese families. Genomic DNA was isolated from the peripheralleukocytes of the subjects using the Puregene DNA Isolation Kits. Firstly, 9 hot spotsfor mutations in four most common pathologic genes, GJB2 (35delG, 176del16bp,235delC and 299delAT), GJB3 (C538T ), SLC26A4 (IVS7-2A>G, A2168G) andmitochondria 12S rRNA (A1555G, C1494T), were screened with the DNA microarrayto detect the deafness-associated mutations. The whole mitochondrial genomes andthe coding sequence of TRMU and MTO1 genes of two probands were then PCRamplified using specific primers. Each fragment was purified and subsequentlyanalyzed by direct sequencing in an Applied Biosystems 3730 automated DNAsequencer. The resultant sequence data were compared with the standard sequence toidentify base changes.Results:Mitochondrial 12S rRNA C1494T mutation was detected in all 7 maternalmembers of the two families. Sequence analysis of the complete mitochondrialgenomes in the two probands revealed the distinct sets of mitochondrial DNApolymorphism (52 other nucleotide changes), in addition to the identical 12S rRNAC1494T mutation. None of these 52 variants, however, were shown to be pathogenic.The whole mitochondrial genome of proband from each of the two families wasestablished that they belong to mitochondrial haplogroups D4 and D5a respectively.No mutations were identified in either TRMU gene or MTO1 gene. Conclusions:C1494T mutation in the mitochondrial 12S rRNA gene is the main molecularmechanism responsible for the hearing loss in the two pedigrees, and the use ofaminoglycoside antibiotics may enhance the phenotypic manifestation of deafness-associated mitochondrial C1494T mutation. Mitochondrial haplogroups and nucleargenes of TRMU and MTO1, however, seem not contribute to the phenotypicexpression of C1494T mutation in these two families.