gms | German Medical Science

Introduction: Sensorineural hearing loss (SHL) occurs mainly in patients bearing mutation in GJB2 gene (in Europeans it is most often the deletion 35delG). A lot of mitochondrial DNA mutations were reported to be the cause of deafness as well, each of them as a rare event (less than 2% of the whole patients group). These are most often detected in 12SrRNA and tRNAser genes. The aim of the study was to define the rates of two mitochondrial mutations of 12SrRNA gene in Belarus children with bilateral SHL.

Methods: 197 patients were genotyped, DNA was extracted from blood spots by standard method with proteinase K and phenol; PCR-RFLP methods were used for mutation detection in 12SrRNA gene.

Results: T961G mutation in 12SrRNA was detected in 4 patients with SHL (2%), three of these patients are homozygous and one is heterozygous for the nuclear mutation 35delG. Another mutation, A1555G, in the same 12SrRNA gene, was found in one girl (0,5%) with SHL, she also has two copies of nuclear 35delG mutation. Notably that three members of her family are homoplasmic for A1555G mutation but heterozygous for 35delG and all three have normal hearing: it proves that penetration of A1555G is not absolute.

Conclusions: two mitochondrial mutations in 12SrRNA gene were found in Belarus patients with bilateral SHL with the rates 2% and 0,5%. Mutations in 12SrRNA gene were detected in 5 patients having also 35delG GJB2 nuclear mutation in homo- or heterozygous state – this fact is rather intriguing as in other ethnic populations studied the combination of nuclear and mitochondrial mutations of deafness is an extremely rare event.