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Genetics Home Reference: your guide to understanding genetic conditions     A service of the U.S. National Library of Medicine®


Reviewed January 2008

What is galactosemia?

Galactosemia is a disorder that affects how the body processes a simple sugar called galactose. A small amount of galactose is present in many foods. It is primarily part of a larger sugar called lactose, which is found in all dairy products and many baby formulas. The signs and symptoms of galactosemia result from an inability to use galactose to produce energy.

Researchers have identified several types of galactosemia. These conditions are each caused by mutations in a particular gene, and affect different enzymes involved in breaking down galactose. Classic galactosemia, also known as type I, is the most common and most severe form of the condition. Galactosemia type II (also called galactokinase deficiency) and type III (also called galactose epimerase deficiency) cause different patterns of signs and symptoms.

If infants with classic galactosemia are not treated promptly with a low-galactose diet, life-threatening complications appear within a few days after birth. Affected infants typically develop feeding difficulties, a lack of energy (lethargy), a failure to gain weight and grow as expected (failure to thrive), yellowing of the skin and whites of the eyes (jaundice), liver damage, and bleeding. Other serious complications of this condition can include overwhelming bacterial infections (sepsis) and shock. Affected children are also at increased risk of delayed development, clouding of the lens of the eye (cataract), speech difficulties, and intellectual disability. Females with classic galactosemia may experience reproductive problems caused by ovarian failure.

Galactosemia type II causes fewer medical problems than the classic type. Affected infants develop cataracts, but otherwise experience few long-term complications. The signs and symptoms of galactosemia type III vary from mild to severe and can include cataracts, delayed growth and development, intellectual disability, liver disease, and kidney problems.

How common is galactosemia?

Classic galactosemia occurs in 1 in 30,000 to 60,000 newborns. Galactosemia type II and type III are less common; type II probably affects fewer than 1 in 100,000 newborns and type III appears to be very rare.

What genes are related to galactosemia?

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

The GALE, GALK1, and GALT genes provide instructions for making enzymes that are essential for processing galactose obtained from the diet. These enzymes break down galactose into another simple sugar, glucose, and other molecules that the body can store or use for energy.

Mutations in the GALT gene are responsible for classic galactosemia (type I). Most of these genetic changes almost completely eliminate the activity of the enzyme produced from the GALT gene, preventing the normal processing of galactose and resulting in the life-threatening signs and symptoms of this disorder. Another GALT gene mutation, known as the Duarte variant, reduces but does not eliminate the activity of the enzyme. People with the Duarte variant tend to have much milder features of galactosemia.

Galactosemia type II results from mutations in the GALK1 gene, while mutations in the GALE gene underlie galactosemia type III. Like the enzyme produced from the GALT gene, the enzymes made from the GALK1 and GALE genes play important roles in processing galactose. A shortage of any of these critical enzymes allows galactose and related compounds to build up to toxic levels in the body. The accumulation of these substances damages tissues and organs, leading to the characteristic features of galactosemia.

Related Gene(s)

Changes in these genes are associated with galactosemia.

  • GALE
  • GALK1
  • GALT

How do people inherit galactosemia?

This condition is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have mutations. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene, but they typically do not show signs and symptoms of the condition.

Where can I find information about diagnosis or management of galactosemia?

These resources address the diagnosis or management of galactosemia and may include treatment providers.

  • Baby's First Test: Classic Galactosemia (
  • Baby's First Test: Galactoepimerase Deficiency (
  • Baby's First Test: Galactokinase Deficiency (
  • Gene Review: Classic Galactosemia and Clinical Variant Galactosemia (
  • Gene Review: Duarte Variant Galactosemia (
  • Gene Review: Epimerase Deficiency Galactosemia (
  • Genetic Testing Registry: Deficiency of galactokinase (
  • Genetic Testing Registry: Deficiency of UDPglucose-hexose-1-phosphate uridylyltransferase (
  • Genetic Testing Registry: Galactosemia (
  • Genetic Testing Registry: UDPglucose-4-epimerase deficiency (
  • MedlinePlus Encyclopedia: Galactose-1-phosphate uridyltransferase (
  • MedlinePlus Encyclopedia: Galactosemia (

You might also find information on the diagnosis or management of galactosemia in Educational resources and Patient support.

General information about the diagnosis ( and management ( of genetic conditions is available in the Handbook. Read more about genetic testing (, particularly the difference between clinical tests and research tests (

To locate a healthcare provider, see How can I find a genetics professional in my area? ( in the Handbook.

Where can I find additional information about galactosemia?

You may find the following resources about galactosemia helpful. These materials are written for the general public.

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

What other names do people use for galactosemia?

  • Classic Galactosemia
  • Epimerase deficiency galactosemia
  • Galactokinase Deficiency Disease
  • Galactose-1-Phosphate Uridyl-Transferase Deficiency Disease
  • Galactose epimerase deficiency
  • GALT Deficiency
  • UDP-Galactose-4-Epimerase Deficiency Disease
  • UDPglucose 4-Epimerase Deficiency Disease
  • UDPglucose Hexose-1-Phosphate Uridylyltransferase Deficiency
  • UTP Hexose-1-Phosphate Uridylyltransferase Deficiency

For more information about naming genetic conditions, see the Genetics Home Reference Condition Naming Guidelines ( and How are genetic conditions and genes named? ( in the Handbook.

What if I still have specific questions about galactosemia?

Ask the Genetic and Rare Diseases Information Center (

What glossary definitions help with understanding galactosemia?

autosomal ; autosomal recessive ; cataract ; cell ; deficiency ; disability ; enzyme ; failure to thrive ; galactose ; gene ; glucose ; inherited ; jaundice ; kidney ; lethargy ; mutation ; newborn screening ; ovarian ; phosphate ; recessive ; screening ; sepsis ; shock ; simple sugar ; toxic ; transferase

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.


  • Arn PH. Galactosemia. Curr Treat Options Neurol. 2003 Jul;5(4):343-345. (
  • Bosch AM. Classical galactosaemia revisited. J Inherit Metab Dis. 2006 Aug;29(4):516-25. Epub 2006 Jul 11. Review. (
  • Dobrowolski SF, Banas RA, Suzow JG, Berkley M, Naylor EW. Analysis of common mutations in the galactose-1-phosphate uridyl transferase gene: new assays to increase the sensitivity and specificity of newborn screening for galactosemia. J Mol Diagn. 2003 Feb;5(1):42-7. (
  • Fridovich-Keil JL. Galactosemia: the good, the bad, and the unknown. J Cell Physiol. 2006 Dec;209(3):701-5. Review. (
  • Gene Review: Classic Galactosemia and Clinical Variant Galactosemia (
  • Lai K, Willis AC, Elsas LJ. The biochemical role of glutamine 188 in human galactose-1-phosphate uridyltransferase. J Biol Chem. 1999 Mar 5;274(10):6559-66. (
  • Leslie ND. Insights into the pathogenesis of galactosemia. Annu Rev Nutr. 2003;23:59-80. Epub 2003 Apr 9. Review. (
  • Novelli G, Reichardt JK. Molecular basis of disorders of human galactose metabolism: past, present, and future. Mol Genet Metab. 2000 Sep-Oct;71(1-2):62-5. Review. (
  • Openo KK, Schulz JM, Vargas CA, Orton CS, Epstein MP, Schnur RE, Scaglia F, Berry GT, Gottesman GS, Ficicioglu C, Slonim AE, Schroer RJ, Yu C, Rangel VE, Keenan J, Lamance K, Fridovich-Keil JL. Epimerase-deficiency galactosemia is not a binary condition. Am J Hum Genet. 2006 Jan;78(1):89-102. Epub 2005 Nov 14. (
  • Ridel KR, Leslie ND, Gilbert DL. An updated review of the long-term neurological effects of galactosemia. Pediatr Neurol. 2005 Sep;33(3):153-61. Review. (
  • Suzuki M, West C, Beutler E. Large-scale molecular screening for galactosemia alleles in a pan-ethnic population. Hum Genet. 2001 Aug;109(2):210-5. (


The resources on this site should not be used as a substitute for professional medical care or advice. Users seeking information about a personal genetic disease, syndrome, or condition should consult with a qualified healthcare professional. See How can I find a genetics professional in my area? ( in the Handbook.

Reviewed: January 2008
Published: July 19, 2015