The authors also showed that peripheral blood cells from patients bearing the A3243G mt-tRNALeu(UUG) mutation, which causes MIDD and mitochondrial encephalopathy, lactic acidosis, and stroke-like episodes, have reduced ms2 modification in the four CDK5RAP1 mt-tRNA substrates (mt-tRNASer(UCN), mt-tRNATrp, mt-tRNAPhe and mt-tRNATyr), while no change was seen in the methythiolation of the CDKAL1 cytosolic substrate tRNALys(UUU). The gene discussed is CDK5RAP1; the disease is lactic acidosis.