[Inherited and acquired disorders of mitochondrial DNA]

Human mitochondrial DNA (mtDNA) resides in thousands of copies in each cell and encodes for 13 structural proteins which are subunits of the respiratory chain. Point mutations, deletions, and decreased copy-number (mtDNA-depletion) are now functionally and genetically linked to human disease. Although mtDNA is inherited maternally, some mutations may arise spontaneously and others are inherited in a mendelian fashion, which is attributed to defective nuclear genes. MtDNA-mutations are also associated with aging and with tumors but in these conditions probably not of functional significance. Mutations of mtDNA may be acquired by exposure to toxic substances (such as alcohol or doxorubicin). An acquired copy number defect (mtDNA-depletion) is dose-limiting for some antiviral nucleosides and nucleotide analogues. The internist encounters predominantly myopathies, cardiomyopathies, lactic acidosis or diabetes mellitus but mtDNA-changes also lead to neurological, hematological and renal symptoms. A syndrome of fat redistribution, termed lipodystrophy, is now observed with long-term therapy of HIV-patients and has been associated with mtDNA-depletion. Therapy with vitamins, radical scavengers and L-carnitine is recommended, but of limited success.