MT-ND5 and Leigh syndrome: Furthermore, severe clinical phenotypes associated with a relatively low mutant load have also been observed in other common point mutations in the MT-ND5 gene, including the m.13513G > A mutation, where a mutant load of <50% in muscle has been reported in association with LS (Kirby et al., 2003) and MELAS (Shanske et al., 2008).