25 - Inborn Errors of Carbohydrate Metabolism

Summary

This chapter deals with three inborn errors of carbohydrate metabolism that lead to hepatic dysfunction: galactosemia, hereditary fructose intolerance (HFI), and glycogen storage disease (GSD) types I, III, and IV. The clinical presentation of such patients includes varying degrees of hypoglycemia, acidosis, growth failure, and hepatic dysfunction. Appropriate steps in obtaining clinical history, physical examination, and laboratory evaluation support a definitive diagnosis. Advances in biochemistry and molecular biology, which have made significant contributions toward better understanding of the molecular defects underlying these disorders, are anticipated to result eventually in the development of newer treatment strategies. The newer information is highlighted in this chapter.

GALACTOSEMIA

The first detailed characterization of a galactose-intolerant individual was provided by Mason and Turner in 1935 [1]. Since then, three distinct disorders of galactose metabolism and several variant forms of the disease have been identified. These disorders are transmitted by autosomal recessive inheritance and are expressed as a cellular deficiency of one of three enzymes in the metabolic pathway through which galactose is converted to glucose: galactose-1-phosphate uridyl transferase, galactokinase, and uridine diphosphate (UDP) galactose-4-epimerase. The terms transferase deficiency galactosemia, galactokinase deficiency galactosemia, and epimerase deficiency galactosemia traditionally have been used to distinguish between the various forms of the disease. Until recently, the genetic basis of galactosemia was discerned primarily through quantification of red cell activity of these enzymes.