ABSTRACT
The last decade has led to the identification of several mitochondrial DNA mutations associated with hearing loss. Since the only known function of the human mitochondrial chromosome is to participate in the production of chemical energy through oxidative phosphorylation, it was not unexpected that mitochondrial mutations interfering with energy production could cause systemic neuromuscular disorders, which have as one of their features hearing impairment. Surprisingly, however, inherited mitochondrial mutations have also been found to be a cause of nonsyndromic hearing loss, and predispose to aminoglycoside-induced hearing loss, while acquired mitochondrial mutations have been proposed as one of the causes of presbycusis. This chapter will first give a short background review of mitochondrial genetics, outline the different mitochondrial mutations associated with hearing loss, and discuss the clinical relevance of diagnosing these mutations. The latter part of the chapter will concentrate on the fact that the clinical expression of these mitochondrial mutations is dependent on environmental exposures and nuclear-encoded modifier genes. Preventive and therapeutic strategies will depend on identification and avoidance of the environmental exposures, and the identification of the nuclear-encoded modifier genes. Experimental approaches to identify these modifier genes will be presented.
