Classic galactosemia, as defined in the Online Mendelian Inheritance in Man (OMIM) (230400), is an autosomal recessive disorder caused by a deficiency in galactose-1-phosphate uridylyltransferase (GALT, EC 2.7.7.12) activity [1,2,3,4,5]. The gene discussed is GALT; the disease is classic galactosemia.