Apart from classic/Duarte galactosemia caused by GALT deficiency, deficiencies in other enzymes of the ‘Leloir pathway’ and galactose metabolism are known to cause galactosemia as well: type II galactosemia, caused by deficiency of galactokinase (GALK1), which phosphorylates galactose to galactose-1-phosphate deficiency [5], and type III galactosemia, caused by deficiency of UDP-galactose epimerase (GALE), which catalyzes the isomerization of UDP-galactose [6]. Here, GALK1 is linked to hyperinsulinemic hypoglycemia, familial, 4.