Investigation of the mtDNA mutations in Syrian families with non-syndromic sensorineural hearing loss

Objective: Hearing loss is a common sensory disorder, and at least 50% of cases are due to a genetic etiology. Several mitochondrial DNA mutations (mtDNA) have been reported to be associated with nonsyndromic hearing loss (NSHL) in different population. However, There is no previous available data about the frequency of mtDNA mutations as etiology for deafness in Syrian. The aim of present study is to investigate the incidence of common mt DNA mutations in our families with congenital hearing loss and not related to the ototoxicity or aminoglycosides.

Methods: A total of 50 deaf families were enrolled in the present study. Direct sequencing and PCR-RFLP methods were employed to detect seven mt DNA mutations, including A1555G, A3243G, C1494T, G3316A, T7510C, A7445G, and 7472insC.

Results: Our results revealed a high prevalence of mt DNA mutation (10%) in deaf families (5/50). In surprising, the unexpected mutations were observed. The G3316A mutation was found in 2 families as homoplasmic genotype. Also, we found the homoplasmic and heteroplasmic genotype for the C1494T mutation in two families. In one family the heteroplasmic genotype for T7510C mutation was observed; this family harbor 35delG mutation in GJB2 gene. None of the common mtDNA mutations (A1555G, A3243G) and other mutations (A7445G, 7472insC) were detected here.

Conclusion: Our findings indicate to significant contribution of the mt DNA mutations in our families with NSHL. The presented data is the first report about mt DNA and it will improve the genetic counseling of hearing impaired in Syrian families.