NDUFS4 and Leigh syndrome: Humans harboring mutations in NDUFS4, a subunit of the mitochondrial complex I involved in the assembly and stability of the complex (Scacco et al., 2003; Kruse et al., 2008; Calvaruso et al., 2012) develop Leigh Syndrome (LS), a severe form of MD (DiMauro and Schon, 2008).