It is interesting that, similar to Riknull animals, mice deficient in a subunit of mitochondrial complex I, NADH:ubiquinone oxidoreductase core subunit S4 (Ndufs4), which is a model of Leigh syndrome [32], were born healthy [33], but by P21, they lagged behind in growth, developed ataxia and died prematurely. The gene discussed is NDUFS4; the disease is cerebellar ataxia.