MITOCHONDRIAL DEAFNESS

Hearing impairment is a common disorder, largely genetic in origin, an d showing classical features of a heterogeneous genetic disease. Up to 100 independently acting nuclear genes are involved in the disorder, of which around 30 have been mapped, but only a handful identified. Mu tations in mitochondrial DNA also play a significant role in both synd romic and nonsyndromic sensorineural hearing impairment. Environmental agents such as aminoglycoside antibiotics and as yet unidentified nuc lear genes interact with mitochondrial mutations in the expression of auditory phenotypes. The spectrum of different mitochondrial mutations associated with hearing impairment, taken together with mechanistic s tudies at the molecular revel, suggests that the pathogenic process in volves the accumulation of abnormal translation products inside mitoch ondria, in sensitive cells of the auditory system. This leads to a pre diction of the involvement of a novel class of nuclear genes in hearin g impairment, namely those with roles in 'mitochondrial protein qualit y control'.