MT-ND2 and lactic acidosis: The clinical pictures reported are usually remarkably similar, with patients often presenting with exercise intolerance, muscle weakness and sometimes with high level of lactate at rest: an MT-ND2 heteroplasmic mutation (m.4831G>A), consisting of a transition of the p.Gly121Asp in the ND2 protein, was described by Zanolini A et al. in a young patient complaining about exertion-related muscle weakness and lactic acidosis [33], and similar cases are reported as consequences of MT-ND4 and MT-ND5 point mutations [34,35].