IARS2 and Leigh syndrome: Presently, most of the CAGSSS pathogenic missense variants that have been identified reside in exon 21 (Gly874Arg, Pro909Leu, Pro909Ser) of IARS2. It remains unknown whether homozygous variants in this exon tend to be associated with CAGSSS and variants of unknown significance in other affected exons are responsible for Leigh syndrome, a syndrome that is attributed to the death of a patient at 18 months of age that was proposed to be due to compound heterozygous IARS2 variants (c.1821G > A, p.Trp607* in exon 14 and c.2122G > A, p.Glu708Lys in exon 17) [5].