We explored the mitochondrial 12S rRNA and the tRNA(Ser(UCN)) genes in 100 Tunisian families affected with NSHL and in 100 control individuals. We identified the mitochondrial A1555G mutation in one Out of these 100 families and not in the 100 control individuals. Members of this family harbouring the A1555G mutation showed phenotypic heterogeneity which could be explained by an eventual nuclear-mitochondrial interaction. So, we have screened three nuclear genes: GJB2, GJB3, and GJB6 but we have not found correlation between the phenotypic heterogeneity and variants detected in these genes. We explored also the entire mitochondrial 12S rRNA and the tRNA(Ser(UCN)) genes. We detected five novel polymorphisms: T742C, T794A, AS813G, C868T, and C954T, and 12 known polymorphisms in the mitochondrial 12S rRNA gene. None of the 100 families or the 100 controls were found to carry mutations in the tRNA(Ser(UCN)) gene. We report here the first mutational screening of the mitochondrial 12S rRNA and the tRNA (Ser(UCN)) genes in the Tunisian population which describes the second family harbouring the A1555G mutation in Africa and reveals novel polymorphisms in the mitochondrial 12S rRNA gene. (c) 2005 Elsevier Inc. All rights reserved.