Eric Shoubridge’s laboratory focuses on the molecular genetics of mitochondrial diseases, in particular, those that affect the function of the respiratory chain. Mitochondria are essential for a number of cellular processes such as heme and iron-sulfur cluster biosynthesis, and for aerobic energy production. Energy production occurs in the respiratory chain, a system composed of five multi-subunit enzyme complexes whose polypeptide components are encoded in both the nuclear and mitochondrial genomes (mtDNA). Although only a handful of polypeptides are encoded in mtDNA, all are essential. Defects in respiratory chain function have been linked to a wide spectrum of multi-system disorders, often referred to as encephalomyopathies because of the prominent involvement of the nervous system and skeletal muscle. These defects have an estimated prevalence of one in every five thousand births. Defects can be caused by mutations in nuclear genes or in mtDNA.