GALK1 (galactokinase 1) catalyzes the phosphorylation of galactose to galactose-1-phosphate, representing the first committed step in galactose catabolism via the Leloir pathway 1. The enzyme is a cytosolic protein encoded by an 8-exon gene on chromosome 17 with housekeeping gene characteristics 1. GALK1 is the predominant galactokinase in humans, with substantially higher enzymatic activity than the related GK2 protein 2. Autosomal recessive GALK1 mutations cause galactokinase deficiency (Type II galactosemia), characterized by elevated blood galactose and accumulation of galactitol 3. Beyond the classical neonatal or infantile cataract manifestation, GALK1 deficiency may present with elevated transaminases, bleeding diathesis, encephalopathy, and cognitive delay 4. Missense mutations and insertions result in reduced enzyme activity 3. GALK1 participates critically in O-linked glycosylation through the galactose/GalNAc salvage pathway; knockout studies show that simultaneous disruption of galactose-metabolizing enzymes (GALE+GALK1) eliminates O-glycosylation 5. Beyond galactosemia, emerging evidence suggests GALK1 inhibition may provide therapeutic benefit in classic galactosemia by reducing toxic metabolite accumulation 6, and GALK1 has been identified as a potential biomarker in atopic dermatitis and bladder cancer 78.