GALM (galactose mutarotase) catalyzes the interconversion of β-D-galactose and α-D-galactose during galactose metabolism 1. As the first enzyme in the Leloir pathway, GALM maintains equilibrium between galactose anomers, ensuring sufficient α-anomer substrate for GALK1, the next pathway enzyme 1. The enzyme uses a catalytic mechanism involving histidine and glutamate residues that open the pyranose ring structure, enabling anomeric interconversion 2. GALM shows substrate preference for galactose over glucose 1. Biallelic GALM pathogenic variants cause Type IV galactosemia, characterized by elevated blood galactose levels and early-onset bilateral cataracts 3. Missense mutations (R78S, R82G, A163E, P210S, Y281C, E307G, F339C) impair enzyme function through reduced substrate binding, increased protein rigidity, and altered protein stability 4. Beyond galactosemia, emerging evidence suggests GALM participates in Alzheimer's disease pathology: GALM overexpression reduces amyloid-β deposition by increasing ADAM10 maturation and ameliorates cognitive deficits in AD model mice 5. Current treatment for GALM deficiency relies on galactose dietary restriction; however, β-galactosidase supplementation shows promise in mitigating blood galactose elevation after lactose exposure 6.