GJB2 35delG and Mitochondrial A1555G Mutations and Etiology of Deafness at the Gelibolu School for the Deaf in Turkey

Objective: 35delG mutation in the GJB2 (gap junction protein beta 2, connexin 26) gene is the most frequent mutation in patients with non-syndromic autosomal recessive deafness. The A1555G mutation in the mitochondrial 12S rRNA is another important genetic alteration, and is associated with aminoglycoside-induced deafness. The aim of this study was to explore the etiology of deafness and the prevalence of both mutations in the study cases. Materials and Methods: We examined audiological and dysmorphological features of all children at the Gelibolu School for the deaf. A questionnaire investigating prenatal, perinatal and postnatal etiological causes of deafness was prepared, and pedigree analysis was performed for each individual. After ENT examination, audiological tests and mutation analysis with the RT PCR method were carried out. Results: The GJB2 35delG and mitochondrial A1555G mutations were detected in 12% and 10% of all deaf school children, respectively. The percentages of genetic, acquired, both genetic and environmental, and unknown etiologies were 62.5, 20.3, 15.6 and 1.6, respectively. One patient had both Waardenburg Syndrome and the mitochondrial A1555G mutation, and one patient carried both 35delG and mitochondria! A1555G mutations. Interestingly, one sporadic case, who developed deafness after fever and aminoglycoside treatment, was found to have a homozygous 35delG mutation. His parents and healthy brother were heterozygous for the mutation. Discussion: Our results showed that dysmorphologic examination and mutation analysis are important for the clarification of etiology, and that they can be helpful for genetic counselling.