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.

[1] In the biallelic form, there is typically a Leigh syndrome phenotype with symptoms including seizures, white matter lesions, nystagmus, developmental delay, microcephaly, leukodystrophy, hypertonia, multiorgan failure, spasticity, tetraparesis, and more.

In severe cases where multiple organ systems are affected, death can occur in early life due to multisystem failure.

[2] There is no cure for CII deficiency, though some reported patients showed clinical improvement following riboflavin therapy, a vitamin essential for mitochondrial function.

As human mitochondrial diseases and the effects of herbicides and fungicides on the mitochondria are a current area of research, our understanding of CII deficiency may progress significantly.