GALK1, also often designated galactokinase, is important in the first step of the galactose metabolism pathway. (ATP + D-galactose = ADP + alpha-D-galactose 1-phosphate) Defects in GALK1 are the cause of galactosemia II. It is an autosomal recessive deficiency characterized by congenital cataracts during infancy and presenile cataracts in the adult population.