We have analyzed the pathogenic role of a novel homoplasmic mutation (m.15533 A>G) in the cytochrome b (MT-CYB) gene in a patient presenting with lactic acidosis, seizures, mild mental delay, and behaviour abnormalities.
Clinical and laboratory data indicate that this defect is the primary cause of the disease, thus adding a new mutation in the cytochrome b gene among the growing number of patients with exercise intolerance and lactic acidosis.
We sequenced the mtDNA cytochrome b gene in blood and muscle specimens from five patients with severe exercise intolerance, lactic acidosis in the resting state (in four patients), and biochemical evidence of complex III deficiency.