Classic Galactosemia is an inherited metabolic disorder that affects the body's ability to process galactose, a sugar found in milk and other dairy products. The condition is caused by a deficiency in the enzyme galactose-1-phosphate uridyltransferase (GALT) which leads to a buildup of toxic substances in the body. Symptoms of classic galactosemia can include vomiting, diarrhea, liver damage, developmental delays, and intellectual disability.