Are GJB2 mutations an aggravating factor in the phenotypic expression of mitochondrial non-syndromic deafness?

Abstract

Hearing impairment is a frequent condition, and genes have an important role in its etiology. The majority of hearing loss occurs in non-syndromic form, with deafness being the only clinically recognizable feature. More than 60 nuclear genes or loci have been shown to be involved in non-syndromic hearing loss, but mutations in mitochondrial DNA also cause hearing impairment. Mitochondrial DNA mutations usually lead to progressive hearing loss with an age of onset varying from childhood to early adulthood. It is interesting to note that there is a great variability among phenotypes between individuals harboring the same mitochondrial mutation, even within the same family, and the phenotype may range from profound deafness to completely normal hearing. In the past years, the debate on mitochondrial mutations has been about the penetrance, the tissue specificity and the mechanisms of modifier genes that can modulate the severity of the phenotypic expression of the deafness-associated mitochondrial DNA mutations. Here we summarize evidence regarding modifying genes, and we discuss the effect of the coexistence of mitochondrial and GJB2 mutations in families reported to date.

Spectrum of Genetic Changes in Patients with Non-Syndromic Hearing Impairment and Extremely High Carrier Frequency of 35delG GJB2 Mutation in Belarus

“…Over 100 loci, both nuclear and mitochondrial, are already implicated in the development of this most common sensory disorder of humans [1]. The GJB gene family (GJB2, GJB3 and GJB6) encoding gene gap junction proteins – connexins – was found to be the main “storage place" of mutations causing non-syndromic sensorineural hearing loss (SNHL) [2]–[4]. More than 50% of cases of autosomal recessive non-syndromic hearing loss in many world populations are attributed to mutations in GJB2 gene encoding connexin 26 (OMIM: 121011) [5].…”