A novel deficiency of mitochondrial ATPase of nuclear origin

We report a new type of fatal mitochondrial disorder caused by selective de ficiency of mitochondrial ATP synthase (ATPase), A hypotrophic newborn from a consanguineous marriage presented severe lactic acidosis, cardiomegaly a nd hepatomegaly and died from heart failure after 2 days. The activity of o ligomycin-sensitive ATPase was only 31-34% of the control, both in muscle a nd heart, but the activities of cytochrome c oxidase, citrate synthase and pyruvate dehydrogenase were normal. Electrophoretic and western blot analys is revealed selective reduction of ATPase complex but normal levels of the respiratory chain complexes I, III and IV. The same selective deficiency of ATPase was found in cultured skin fibroblasts which showed similar decreas es in ATPase content, ATPase hydrolytic activity and level of substrate-dep endent ATP synthesis (20-25, 18 and 29-33% of the control, respectively), P ulse-chase labelling of patient fibroblasts revealed low incorporation of [ S-35]methionine into assembled ATPase complexes, but increased incorporatio n into immunoprecipitated ATPase subunit b, which had a very short half-lif e. In contrast, no difference was found in the size and subunit composition of the assembled and newly produced ATPase complex, Transmitochondrial cyb rids prepared from enucleated fibroblasts of the patient and rho degrees ce lls derived from 143B.TK- human osteosarcoma cells fully restored the ATPas e activity, ATP synthesis and ATPase content, when compared with control cy brids, Likewise, the pattern of [S-35]methionine labelling of ATPase was fo und to be normal in patient cybrids, We conclude that the generalized defic iency of mitochondrial ATPase described is of nuclear origin and is caused by altered biosynthesis of the enzyme.