We carried out whole-genome homozygosity mapping, gene expression analysis and DNA sequencing in individuals with isolated mitochondrial ATP synthase deficiency and identified disease-causing mutations in TMEM70. Complementation of the cell lines of these individuals with wild-type TMEM70 restored biogenesis and metabolic function of the enzyme complex. Our results show that TMEM70 is involved in mitochondrial ATP synthase biogenesis in higher eukaryotes.

The F o F 1 -ATPase, a multisubunit protein complex of the inner mitochondrial membrane, produces most of the ATP in mammalian cells. Mitochondrial diseases as a result of a dysfunction of ATPase can be caused by mutations in mitochondrial DNA-encoded ATPase subunit a or rarely by an ATPase defect of nuclear origin. Here we present a detailed functional and immunochemical analysis of a new case of selective and generalized ATPase deficiency found in an Austrian patient. The defect manifested with developmental delay, muscle hypotonia, failure to thrive, ptosis, and varying lactic acidemia (up to 12 mmol/L) beginning from the neonatal period. A low-degree dilated cardiomyopathy of the left ventricle developed between the age of 1 and 2 y. A Ͼ90% decrease in oligomycin-sensitive ATPase activity and an 86% decrease in the content of the ATPase complex was found in muscle mitochondria. It was associated with a significant decrease of ADP-stimulated respiration of succinate (1.5-fold) and respiratory control with ADP (1.7-fold) in permeabilized muscle fibers, and with a slight decrease of the respiratory chain complex I and compensatory increase in the content of complexes III and IV. The same ATPase deficiency without an increase in respiratory chain complexes was found in fibroblasts, suggesting a generalized defect with tissue-specific manifestation. Absence of any mutations in mitochondrial ATP6 and ATP8 genes indicates a nuclear origin of the defect. Mitochondrial disorders caused by impairment of mitochondrial oxidative phosphorylation (OXPHOS) affect predominantly tissues with high-energy demands: muscle, brain, and heart. Subunits of OXPHOS complexes are encoded in two separate genomes: nuclear and mitochondrial. A pathogenic mutation in both genomes can cause an OX-PHOS defect. Defects in complex V-mitochondrial F o F 1 -ATPase are less frequent than the defects of the respiratory chain complexes, but they are mostly very severe and can be caused by mitochondrial DNA (mtDNA) mutations or by mutations in nuclear genes.Mitochondrial ATPase is a multisubunit complex composed of 16 different subunits (1). Six of these compose the globular F 1 part, which is responsible for enzymatic catalysis of ATP synthesis or hydrolysis. Ten remaining subunits form the membrane-spanning F o part, which performs H ϩ translocation across the inner mitochondrial membrane. Four subunits of F o form stalks that connect F 1 and F o parts. Only two subunits from F o part are encoded by mitochondrial genome: subunits a and A6L (subunits 6 and 8) (2). All of the other 14 subunits of the ATPase are encoded by the nuclear genes.Specific defects in mitochondrial ATPase are caused mainly by mtDNA mutations that affect subunit a; no mutations in subunit A6L have been described so far. The most frequent mutation in subunit a is T8993G mutation (3-7) or T8993C mutation (8)

No abstract