Galactosemia Diagnosis Gets an Upgrade

Abstract

Classic galactosemia, a defect of the metabolism of galactose, was one of the earliest defects of intermediary metabolism to be recognized in the mid 20th century(1)(2). The disease is caused by a defect of galactose-1-phosphate uridyltransferase (GALT),1 an enzyme central to the Leloir pathway in which galactose is converted into glucose. Galactose is primarily derived from the lactose content of milk that a newborn receives. The well-described and frequently taught clinical phenotype of an untreated newborn with classic galactosemia begins shortly after the onset of regular milk feeding and includes feeding intolerance with vomiting and diarrhea caused by galactose fermentation in the gut; hepatic failure leading to jaundice; bleeding manifestations; hypoalbuminemia and hypoglycemia; a renal Fanconi syndrome with loss of phosphate, glucose, and amino acids; congenital bilateral cataracts; and susceptibility to fatal gram-negative sepsis (primarily Escherichia coli ). The hepatic and renal manifestations are caused by intracellular accumulation of galactose 1-phosphate, the substrate for GALT. Cataracts are due to an alternative metabolic pathway of galactose in the lens that leads to galactitol accumulation. Treatment is relatively simple. Once the diagnosis is suspected or confirmed, lactose and lactose-containing products are removed from the diet to reduce the metabolic burden, and most of the neonatal toxicities are alleviated. Subsequent to the recognition of GALT deficiency, 2 additional enzymatic defects of galactose metabolism that also caused galactose accumulation were identified. Galactokinase (GALK) converts galactose to galactose 1-phosphate. GALK deficiency leads to failure to generate the cytotoxic galactose 1-phosphate and therefore does not have the potentially fatal hepatic and renal manifestations. GALK-deficient patients are still at high risk for developing cataracts, which may be congenital or may develop later in life(3). The third enzyme is UDP-galactose 4-epimerase (GALE), which converts UDP-galactose to UDP-glucose, which subsequently is converted to glucose or …