Mutations in the gene coding for the third enzyme of this pathway, galactose-1-phosphate uridylyltransferase (GALT), which catalyzes the transfer of a uridine monophosphate (UMP) group from uridine diphosphate (UDP)-glucose to galactose 1-phosphate, thereby generating glucose 1-phosphate and UDP-galactose, cause the inborn error of metabolism known as “classic galactosemia” (OMIM: #230400). The gene discussed is GALT; the disease is classic galactosemia.