A novel form of mitochondrial disease caused by mutations in MTO1, encoding the mitochondrial tRNA translation optimization 1 (MTO1) protein (OMIM#614667) was first described in 2012 in 2 Italian siblings, born of unrelated parents, presenting soon after birth with lactic acidosis, severe hypoglycaemia and fatal infantile hypertrophic cardiomyopathy [6], [7]. The gene discussed is MTO1; the disease is lactic acidosis.