Classic galactosemia (OMIM #230400) is an autosomal recessive disorder caused by mutations in the GALT gene, resulting in deficient activity of galactose-1-phosphate uridylyltransferase (GALT, EC 2.7.7.12), a key enzyme in galactose metabolism (Fridovich-Keil and Walter 2008). The gene discussed is GALT; the disease is classic galactosemia.