Maternally transmitted nonsyndromic hearing impairment may be associated with mitochondrial tRNA(Ala) 5601C>T and tRNA(Leu(CUN)) 12311T>C mutations

BACKGROUND: Sequence alternations in mitochondrial genomes, especially in genes encoding mitochondrial tRNA (mt‐tRNA), were the important contributors to nonsyndromic hearing loss (NSHL); however, the molecular mechanisms remained largely undetermined. METHODS: A maternally transmitted Chinese pedigree with NSHL underwent clinical, genetic, and biochemical assessment. PCR and direct sequence analyses were performed to detect mitochondrial DNA (mtDNA), GJB2, and SLC26A4 gene mutations from matrilineal relatives of this family. Mitochondrial functions including mitochondrial membrane potential (MMP), ATP, and ROS were evaluated in polymononuclear leukocytes (PMNs) derived from three deaf patients and three controls from this pedigree. RESULTS: Four of nine matrilineal relatives developed hearing loss at the variable age of onset. Two putative pathogenic mutations, m.5601C>T in tRNA(Ala) and m.12311T>C in tRNA(Leu(CUN)), were identified via PCR‐Sanger sequencing, as well as 34 variants that belonged to mtDNA haplogroup G2b2. Intriguingly, m.5601C>T mutation resided at very conserved nucleotide in the TψC loop of tRNA(Ala) (position 59), while the T‐to‐C substitution at position 12311 located at position 48 in the variable stem of tRNA(Leu(CUN)) and was believed to alter the aminoacylation and the steady‐state level of tRNA. Biochemical analysis revealed the impairment of mitochondrial functions including the significant reductions of ATP and MMP, whereas markedly increased ROS levels were found in PMNs derived from NSHL patients with m.5601C>T and m.12311T>C mutations. However, we did not detect any mutations in GJB2 and SLC26A4 genes. CONCLUSION: Our data indicated that mt‐tRNA(Ala) m.5601C>T and tRNA(Leu(CUN)) 12311T>C mutations were associated with NSHL.