Galactokinase, also known as Galactose kinase, GALK and GALK1, is a protein which belongs to the GHMP kinase family and GalK subfamily. Galactokinase / GALK1 is a major enzyme for galactose metabolism. Galactokinase (GALK) deficiency is an autosomal recessive disorder characterized by elevation of blood galactose concentration and diminished galactose-1-phosphate, leading to the production of galactitol. Defects in GALK1 are the cause of galactosemia II ( GALCT2 ) which II is an autosomal recessive deficiency characterized by congenital cataracts during infancy and presenile cataracts in the adult population. The cataracts are secondary to accumulation of galactitol in the lenses.