The clinical phenotype of our patient—characterized by significant developmental delay, progressive microcephaly, movement disorder, and multiorgan involvement (including hepatic, hematologic, auditory, and ocular features), along with mild lactic acidosis and brain calcifications—raised clinical suspicion of a mitochondrial disorder, particularly a KARS1-related disorder, from the first evaluation. This evidence concerns the gene KARS1 and lactic acidosis.