NDUFB6 and spinocerebellar ataxia with epilepsy: CI and cytochrome C oxidase deficiencies, CII deficiency, DCMA, Kearns-Sayre syndrome, Leigh syndrome, LHON, MELAS, MERRF, Methylmalonic aciduria, MLASA, MIDD, PEO, Propionic aciduria, SANDO, SCAE