This report describes general characteristics of the group of diseases classified as mitochondrial complex II deficiency, nuclear type (MC2DN). MC2DN is a genetically heterogeneous disorder, with multiple genes and mapped loci. A comprehensive list of MC2DN subtypes, as defined by OMIM, can be found by following the link in the "OMIM phenotypic series" section, below. A subset of these are listed in the table below, with links to more detailed reports for subtypes that have been investigated using fly models.
Mitochondrial complex II (also known as succinate:ubiquinone oxidoreductase or succinate dehydrogenase) is the second enzyme in the mitochondrial respiratory electron transport chain; this enzyme also participates in the citric acid cycle. It is formed from four subunits: catalytic subunits SDHA and SDHB, and anchoring subunits SDHC and SDHD.
[updated Jun. 2021 by FlyBase; FBrf0222196]
Mitochondrial complex II deficiency is an autosomal recessive multisystemic metabolic disorder with a highly variable phenotype. Some patients have multisystem involvement of the brain, heart, and muscle with onset in infancy, whereas others have only isolated cardiac or muscle involvement. Measurement of complex II activity in muscle is the most reliable means of diagnosis; however, there is no clear correlation between residual complex II activity and severity or clinical outcome. In some cases, treatment with riboflavin may have clinical benefit (summary by Jain-Ghai et al., 2013; pubmed:23322652). [from MIM:252011; 2021.06.15]
