GALT (galactose-1-phosphate uridylyltransferase) is a crucial enzyme in galactose metabolism that catalyzes the conversion of galactose-1-phosphate to UDP-galactose in the Leloir pathway 1. The enzyme exhibits significant allelic heterogeneity, with over 150 different mutations documented across various populations, including common variants Q188R, K285N, S135L, and N314D 2. Deficiency in GALT activity causes classical galactosemia, an autosomal recessive disorder that can be fatal in infancy if untreated and may result in long-term complications even with management 1. The Q188R mutation, most common in European populations (60-70% of mutant chr9), is associated with virtually complete loss of enzyme activity and severe phenotype, while K285N accounts for 25-40% of mutations in many European populations and also correlates with severe disease 2. The S135L variant is found almost exclusively in African Americans and may retain some tissue-specific GALT activity 2. Early genetic diagnosis through whole-exome sequencing is critical for identifying compound heterozygous variants and enabling prompt therapeutic intervention 1. The considerable genetic heterogeneity documented contributes significantly to the observed phenotypic variability in galactosemia patients 2.