The main research topic addressed in the biochemistry group is the functional characterization of novel defects of the mitochondrial energy generating system. Nowadays most new genetic defects are identified by exome sequencing and often require further validation. For these validation studies, patients’ fibroblasts and myoblast cell lines are an important tool. The functioning of the mitochondrial ATP production machinery in these cells is examined by ATP production, pyruvate oxidation and oxygen consumption rate measurements, respiratory chain enzyme activity assays, immunohistochemical and Western blot analysis of various mitochondrial enzymes. In addition, a number array of additional tests and technology platforms are available in our center, including a proteomics/metabolomics facility and a microscopy facility. The results of these studies are essential for establishing a diagnosis in patients with new genetic defects and provide new insights in the ethiology of mitochondrial disorders.