Mitochondrial disorders.

Several different types of mitochondrial DNA mutations have now been identified in a wide spectrum of human disorders. There is some correlation between certain of these mutations and the patient's clinical phenotype, although this relationship is not absolute. The mechanisms by which these mutations produce respiratory chain deficiency and the dysfunction of different tissues are unknown. It is becoming increasingly likely that the nuclear genome plays an important role in the expression of the mitochondrial DNA mutation and the pathogenesis of these diseases.