Galactose metabolism and galactosemia

Abstract

1. 1. Galactose forms an integral part of a number of biologically important compounds, such as cerebrosides, mucopolysaccharides and lactose. Most of the galactose present in these substances is not derived directly from ingested galactose but rather is synthesized from glucose and other precursors. 2. 2. Ingested galactose after absorption is transported to the liver, converted to glucose derivatives, and then enters the general “glucose pool.” The enzymatic reactions involved in galactoseglucose interconversion are reviewed. 3. 3. Impairment of galactose utilization occurs in liver disease, thyrotoxicosis, after ingestion of ethanol, and in galactosemia. 4. 4. Galactosemia is a congenital disorder of galactose metabolism which is transmitted by a single recessive gene and is due to the deficiency of the enzyme, galactose-1-phosphate uridyl transferase. The clinical manifestations consist of nutritional failure, hepatosplenomegaly, cataracts and mental retardation. The urine contains galactose, varying types and amounts of aminoacids, and albumin. Most of the clinical manifestations, except the mental changes, usually improve when galactose is removed from the diet. The toxic manifestations may be related to the accumulation of galactose-1-phosphate in the tissues. The presence of galactose-1-phosphate uridyl transferase in normal erythrocytes and its absence in galactosemic cells has provided the basis for a rapid and specific diagnostic test for the disease. 5. 5. Some utilization of galactose occurs in patients with galactosemia and increases as they mature. This may occur by an alternate pathway of galactose metabolism mediated by the enzyme, uridine diphosphogalactose pyrophosphorylase.