Mitochondrial Complex II Deficiency: Types 1–4

Complex II deficiency is a rare type of mitochondrial disorder and peculiar form of autosomal suppressed condition with an extremely mutable phenotype and heterogeneous clinical symptoms with a varying prevalence of 2–23% (Jackson et al. 2013). Mitochondria are complex cell compartments producing more than 90% of the energy the body needs. Mitochondria do not act legitimately in mitochondrial disorders, ensuing decreased energy production, increased cell injury, and cell death. Mitochondrial respiratory complex II is the smallest OXPHOS complex (140 kDa tetramer), located in the inner mitochondrial membrane. Complex II carries out the oxidation of succinate into fumarate within the citric acid cycle and subsequently allocates electrons to ubiquinone in the electron transport chain (ETC) (Jackson et al. 2013; Jain-Ghai et al. 2013). In this deficiency, the signs and symptoms diverge widely from authentic life-threatening indications in childhood to muscle illness starting in adulthood. Patients suffering from mitochondrial complex II deficiency during early childhood have shown defects of the multiple body system, i.e., nervous system, cardiovascular system, muscular system, hepatic system, and excretory system. These defects are followed by mortality, while the onset of the same deficiency in adult patients presented only isolated cardiac or muscle involvement (Jackson et al. 2013; Jain-Ghai et al. 2013; Miki 2002).