Since the discovery of aspartic tRNA synthase deficiency (DARS2) in leukodystrophies with brain stem and spinal cord involvement and lactate elevation (LBSL) in 2007 (9), there have been 14 reported pathogenic mutations that encode the mitochondrial aminoacyl-tRNA synthase gene in neurological diseases, such as mt-AlaRS (AARS2), mt-AsnRS (NARS2), mt-AspRS (DARS2), mt-ArgRS (RARS2), mt-CysRS (CARS2), mt-GluRS (EARS2), mt-HisRS (HARS2), mt-IleRS (IARS2), mt-LeuRS (LARS2), mt-MetRS (MARS2), mt-PheRS (FARS2), mt-ProRS (PARS2), mt-ThrRS (TARS2), and mt-ValRS (VARS2) (14). The gene discussed is MCAT; the disease is hyperinsulinemic hypoglycemia, familial, 4.