Atypical cases of hearing loss in patients with the mitochondrial variant m.1555A>G of the MT-RNR1 gene in the Republic of Buryatia

In the previous study, we found a high prevalence of the m.1555A>G variant of the MT-RNR1 gene, which causes mitochondrial hearing loss (OMIM 561000) among deaf patients living in the Baikal Lake region. In this regard, in the present study, a genotype-phenotypic analysis of the hearing function in individuals with the m.1555A>G variant was carried out in the discovered Siberian region. Clinical and audiological analysis was performed in 48 people with this mitochondrial variant, whose average age was 51.3±15.5 years. The obtained genotype-phenotypic data are consistent with previously conducted studies of the features of the auditory function in individuals with m.1555A>G, which note incomplete penetrance of the manifestation of the pathological phenotype. Of particular interest in our cohort are three cases of mixed hearing loss, including both sensorineural (inner ear defect) and conductive (middle ear defect) components. We do not exclude the possibility that the detected clinical signs may be a consequence of systemic damage to the hearing organ in this mitochondrial variant. On the other hand, the detected cases may be associated with a cross-pathological effect caused by another form of a less common or rare disease, which requires further molecular genetic studies.