Types of Galactosemia

Four types of galactosemia have been identified, all caused by mutations in genes responsible for encoding enzymes that are vital in galactose metabolism. Galactose eventually overflows into the organs and tissues.

Type I: Classic Galactosemia

Classic galactosemia is the most common and severe type of galactosemia resulting from mutations in the GALT gene. Both parents must pass on a defective copy of the GALT gene. GALT deficiency completely prevents the normal processing of galactose by impacting the GALT enzyme, which is essential for metabolizing galactose.

The variant Duarte galactosemia also involves a mutation in the GALT gene, but it is a milder version that only reduces enzyme activity by about 75%. Children with Duarte galactosemia usually do not have serious health effects.

Type II: Galactokinase Deficiency Galactosemia

Galactosemia type II, or galactokinase deficiency galactosemia, is caused by mutations in the GALK1 gene. Like in classic galactosemia, individuals with galactosemia type II cannot fully break down galactose. Though rare, newborns with type II can still develop cataracts, kidney and liver issues, and have delayed growth.

Type III: Epimerase Deficiency Galactosemia

Galactosemia type III, or epimerase deficiency galactosemia, is caused by a mutation in the GALE gene. An inherited mutation can cause different levels of activity loss in the GALE enzyme, ranging from peripheral, intermediate, and generalized (severe). Along with galactosemia type II, newborn screening programs usually do not test for epimerase deficiency.

Type IV: Mutarotase Deficiency Galactosemia

Galactosemia type IV, or mutarotase deficiency galactosemia, is a recently discovered variant that results from mutations in the GALM gene. Galactosemia type IV manifests with similar symptoms as type II, particularly early-onset cataracts. Due to its novelty, its long-term consequences have not been extensively studied.

Complications

Even if children receive treatment early on and follow dietary guidelines, delays in development and cognition are common. Though the level of symptoms will vary from mild to severe, long-term issues may include feeding problems, learning disabilities, neurological impairments, cataracts, and ovarian failure.

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History of Galactosemia

The first documented case of a toxic buildup of galactose in the body was in 1908, with many discoveries and challenges arising in the century since then.

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Diagnosis

Galactosemia is often challenging to diagnose because physical symptoms may not be present immediately after birth. Newborn screening and genetic tests are thus crucial because the earlier galactosemia is identified, the less likely a child will have irreversible complications.

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