Inborn Errors of Carbohydrate Metabolism - Galactose

Galactose

Galactosemia, the inability to metabolize galactose, is the most common monogenic disorder of carbohydrate metabolism, affecting 1 in every 55,000 newborns. When galactose in the body is not broken down, it accumulates in tissues. The most common signs are failure to thrive, hepatic insufficiency, cataracts and developmental delay. Long term disabilities include poor growth, mental retardation, and ovarian failure in females.

Galactosemia is caused by mutations in the gene that makes the enzyme galactose-1-phosphate uridylyltransferase. Approximately 70% of galactosemia-causing alleles have a single missense mutation in exon 6. A milder form of galactosemia, called Galactokinase deficiency, is caused a lack of the enzyme uridine diphosphate galactose-4-epimerase which breaks down a byproduct of galactose. This type of is associated with cataracts, but does not cause growth failure, mental retardation, or hepatic disease. Dietary reduction of galactose is also the treatment but not as severe as in patients with classical galactosemia. This deficiency can be systemic or limited to red blood cells and leukocytes.

Screening is performed by measuring GAL-1-P urydil transferase activity. Early identification affords prompt treatment, which consists largely of eliminating dietary galactose.