Galactosemia: An inherited disorder of galactose metabolism that occurs in newborns and can result in damage to the liver, brain, kidneys, and other organs in infants due to the accumulation of galactose derivatives in the body. Individuals with galactosemia cannot tolerate any amount of human or animal milk intake. The symptoms of galactosemia resolve if a diet that restricts the intake of galactose and lactose is started during the first 10 days of life. Galactosemia is inherited as an autosomal recessive trait. Galactosemia is due to deficient activity of the enzyme galactose-phosphate uridyltransferase (GALT). Molecular testing for the gene that produces GALT permits carrier detection, genetic counseling, and prenatal diagnosis.