Galactosemia classification

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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]; Associate Editor(s)-in-Chief: Dayana Davidis, M.D. [2]

Overview

Galactosemia is an inherited rare autosomal recessive trait that leads to the build up of galactose in the blood. The word galactosemia means too much galactose, which is a simple sugar obtained after lactose, the sugar found in dairy products, is broken down by enzymes found in the body into galactose and glucose.

Classification

Galactosemia Type 1

Galactosemia type 1, also called classic galactosemia is the most common form of the disorder and the first form to be discovered. Individuals diagnosed with classic galactosemia have the genetic makeup G/G, which indicates that they have inherited the galactosemia gene from each parent. They have defects in both copies of the gene that codes for the enzyme galactose-1-phosphate uridyl transferase or GALT.

Duarte galactosemia is a variant of the classic galactosemia. Individuals with the genetic makeup D/G have one gene for classic galactosemia from one parent, G, and one Duarte gene variant from the other parent. Individuals with Duarte galactosemia will be able to metabolize some galactose as GALT activity in Duarte Galactosemia patients is approximately 20% to 50%. Patients with Duarte Galactosemia have less severe symptoms than other forms of the disorder.

Galactosemia Type 2

Galactosemia type 2 is less common than classic galactosemia and is less harmful. It does not generally lead to hepatomegaly or brain damage. It is caused by the defect in both copies of the gene that codes for the enzyme galactokinase or GALK.

Galactosemia type 3

Galactosemia type 3 is a very rare form of the disorder. There are two forms of Galactosemia type 3, a severe form and a benign form. This type of galactosemia is caused by defects in the gene that codes for the enzyme uridyldiphosphogalactose-4-epimerase or GALE.