A rare genetic mitochondrial oxidative phosphorylation disorder that may present with a wide range of symptoms (including muscular hypotonia, hypertrophic cardiomyopathy, psychomotor delay, encephalopathy, peripheral neuropathy, lactic acidosis, 3-methylglutaconic aciduria) and clinical syndromes including Neuropathy, Ataxia, and Retinitis Pigmentosa (NARP) syndrome and Maternally inherited Leigh (MILS) syndrome. [from SNOMEDCT_US]