OBJECTIVETo investigate the genotypes of mitochondrial DNA mutations of a large nonsyndromic inherited hearing impairment pedigree.

METHODSThe diagnosis was validated by hearing test. Blood samples from the branch pedigree (33 members) and 6 sporadic patients were obtained. DNA was extracted from the leukocytes. The mitochondrial DNA target fragments were amplified by polymerase chain reaction(PCR). The 1555G, 3243G and 7445G mutations were detected by BsmA I, Apa I and Xba I restriction endonuclease digestion respectively. Some PCR products were analyzed by sequencing.

RESULTSRestriction endonuclease digestion identified that 17 patients from the pedigree carried 1555G mutation. All pedigree members, including patients and sporadic patients, did not have 3243G and 7445G mutation. In 6 patients of the pedigree DNA sequence analysis revealed double mutations, an A>G transition at position 1555 and a C insertion at position 961, whereas the unaffected relatives of the pedigree and sporadic patients did not have such mutations. None of them carried 3243G and 7445G mutation.

CONCLUSIONDouble mutations of A1555G and 961 insC in mitochondrial DNA 12S rRNA gene region may play a pivotal role in the pathogenesis of hearing loss in the large nonsyndromic inherited hearing impairment pedigree.