Mitochondrial complex II deficiency

Mitochondrial complex II deficiency, also called CII deficiency, is a rare mitochondrial disease caused by deficiency of mitochondrial complex II, also known as Succinate dehydrogenase (SDH). SDH plays a key role in metabolism; the catalytic end, made up of SDHA and SDHB oxidizes succinate to fumarate in the tricarboxylic acid (TCA) cycle. The electrons from this reaction then reduce FAD to FADH2, which ultimately reduces ubiquinone to ubiquinol in the mitochondrial electron transport chain. As of 2020, about 61 cases have been reported with genetic studies, but there are also documented cases of CII deficiencies as determined by biochemical and histological analysis without genetic studies.