We have characterized a mouse model of LS that lacks Ndufs4, a subunit of mitochondrial complex I. These animals (Ndufs4 knockout, KO mice) recapitulate most of the clinical features of human disease such as failure to thrive, hypotonia, ataxia and fatal respiratory failure by about post-natal day 50 (Quintana et al., 2010, 2012b). Here, NDUFS4 is linked to Leigh syndrome.