Mitochondrial mutations: genotype to phenotype.

Diseases associated with defects of the mitochondrial respiratory chain fall into four major categories: (1) those due to mutations in respiratory chain subunits; (2) those due to mutations that affect respiratory chain assembly; (3) those due to mutations that affect respiratory chain function indirectly, either via alterations in the translation of mtDNA-encoded polypeptides or via alterations in mtDNA integrity; and (4) those due to mutations in nDNA that affect organellar morphology and mobility, in which defects in respiratory chain function can be considered to be 'collateral damage'. All four categories will be discussed.