Neurological disease and mitochondrial genes.

Mitochondria contain 2-10 copies of a small, double-stranded, circular DNA molecule that is exclusively maternally transmitted. Until recently, the only function of mitochondrial DNA that had any possible significance for clinicians was the fact that the mutation conferring chloramphenicol resistance occurs in one of the mitochondrial ribosomal RNA genes. It is now clear that major deletions and point mutations of mitochondrial DNA cause human diseases, chiefly mitochondrial myopathies and encephalopathies, and Leber's hereditary optic neuropathy.