OBJECTIVETo analyze the mutations in a pedigree with maternally inherited sensorineural hearing loss, and to investigate whether 235delC heterozygote mutation in gap junction protein beta 2 (GJB2) gene modulates the severity of hearing loss associated with the A1555G mitochondrial mutation.

METHODSThe PCR products were digested with the Alw26 I restriction enzyme, followed by direct sequencing to detect the mitochondrial mutations in 72 members of a core pedigree of an extensive family with matrilineal nonsyndromic deafness; 235delC mutation of the GJB2 gene was screened in this family by using the Apa I restriction enzyme and direct sequencing.

RESULTSThe A1555G mutation of the mitochondrial DNA was present in all 27 members of maternal line, out of them, 21 members had phenotype of deafness (77.8%), with a high penetrance. Only three maternal line members of 72 members possessed 235delC heterozygote mutations, and the three had different phenotypes.

CONCLUSIONThe A1555G homozygous mutation of mitochondrial DNA is the susceptive etiological factor of nonsyndromic deafness in this family, but in the study of this pedigree, the 235delC heterozygous mutation in GJB2 gene may not aggravate the symptoms of hearing loss associated with the A1555G mitochondrial mutation.