Article: Galactosemia

What is galactosemia?

Galactosemia is a disorder that affects how the body processes certain sugars (sugar metabolism). This condition results when the body is not able to process the sugar galactose, which is found in many foods. Galactose also exists as part of another sugar, lactose, found in all dairy products. Liver dysfunction, cataracts (clouding of the lens of the eye), speech problems, and mental impairment are characteristic of this condition if not treated.

How common is galactosemia?

Classic galactosemia is an inherited disorder that occurs in approximately 1 in 30,000 live births. The incidence of the Duarte variant, a mild type of galactosemia, is more common. This variant affects an estimated 1 in 16,000 live births.

What genes are related to galactosemia?

Mutations in the GALE, GALK1, and GALT genes cause galactosemia.

Most cases of galactosemia are categorized as classic, or type I, galactosemia and are caused by mutations in the GALT gene. This gene produces the enzyme galactose-1-phosphate uridyl-transferase, which is important in processing galactose. Mutations in the GALT gene cause two forms of type I galactosemia, classic and Duarte variant. Individuals with the classic type of galactosemia lack nearly all the enzyme activity necessary to metabolize galactose. Individuals with the Duarte variant have approximately 5 to 20 percent of the enzyme activity necessary to metabolize this sugar and often do not have signs or symptoms of galactosemia.

Galactosemia type II results from mutations in the GALK1 gene, which cause a shortage of the enzyme galactokinase. Galactosemia type III results from mutations in the GALE gene, which cause a shortage of the enzyme UDP-galactose-4-epimerase. Both of these enzymes also play a role in the proper metabolism of galactose.

How do people inherit galactosemia?

This condition is inherited in an autosomal recessive pattern, which means two copies of the gene in each cell must be altered for a person to be affected by the disorder. Most often, the parents of a child with an autosomal recessive disorder are not affected but are carriers of one copy of the altered gene.

Source: Genetics Home Reference
Cache Date: April 13, 2005