Patients 3 and 9 were respectively diagnosed with mitochondrial encephalomyopathy, lactic acidosis, and stroke-like episodes (MELAS) and maternally inherited diabetes and deafness (MIDD) caused by a heteroplasmic MT-TL1 (m.3243A>G) mutation; patient 11 had mitochondrial neurogastrointestinal encephalopathy (MNGIE) caused by compound heterozygous TYMP mutations (table). Here, TYMP is linked to mitochondrial encephalomyopathy.