Exercise Intolerance Due to Mutations in the Cytochrome b Gene of Mitochondrial DNA

Exercise intolerance is a common symptom of the encephalomyopathies that are associated with mutations in mitochondrial DNA (mtDNA). 1 , 2 These usually multisystemic disorders include several distinct syndromes: the Kearns–Sayre syndrome; mitochondrial encephalomyopathy, lactic acidosis, and strokelike episodes (the MELAS syndrome); myoclonus epilepsy with ragged-red fibers; Leber's hereditary optic neuropathy; and maternally inherited Leigh's syndrome. All these disorders are transmitted by nonmendelian, maternal inheritance, except the Kearns–Sayre syndrome, which is a sporadic condition. Until recently, little was known about the molecular basis of exercise intolerance as the sole manifestation of mitochondrial dysfunction in patients with sporadic cases. In 1993, Bouzidi et . . .