GTPBP3 and lactic acidosis: In particular, mutations in the nuclear genes GTPBP3 (MIM #608536) and MTO1 (MIM #614667), which encode proteins involved in the post-transcriptional modification of a mitochondrial-tRNA (mt-tRNA) group, cause infantile hypertrophic cardiomyopathy with lactic acidosis and, quite often, neurological symptoms3–9.