Galactosemia is an inherited metabolic deficiency of the galactose-1-phosphate uridyltransferase enzyme. This is one of the most common carbohydrate metabolism disorders and may be life threatening or even fatal in the neonatal period.

The incidence of galactosemia in the United States is about 1:40,000 to 1:60,000 people; worldwide the incidence varies considerably. All races and ethnic groups can be affected, with the Asian population having the lowest occurrence of the disease.

Galactosemia results from alteration of the gene for galactose-1-phosphate uridyltransferase (GALT) found at the 9p13 band.