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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 the official name of the GALT gene?

The official name of this gene is “galactose-1-phosphate uridylyltransferase.”

GALT is the gene's official symbol. The GALT gene is also known by other names, listed below.

What is the normal function of the GALT gene?

The GALT gene provides instructions for making an enzyme called galactose-1-phosphate uridylyltransferase. This enzyme enables the body to process a simple sugar called galactose, which is present in small amounts in many foods. Galactose is primarily part of a larger sugar called lactose, which is found in all dairy products and many baby formulas.

Galactose-1-phosphate uridylyltransferase is responsible for one step in a chemical process that breaks down galactose into other molecules that can be used by the body. Specifically, this enzyme converts a modified form of galactose (galactose-1-phosphate) to glucose, which is another simple sugar. Glucose is the main energy source for most cells. This chemical reaction also produces another form of galactose (UDP-galactose) that is used to build galactose-containing proteins and fats. These modified proteins and fats play critical roles in chemical signaling, building cellular structures, transporting molecules, and producing energy.

How are changes in the GALT gene related to health conditions?

galactosemia - caused by mutations in the GALT gene

More than 180 mutations in the GALT gene have been identified in people with the classic form of galactosemia. Most of these mutations severely reduce or eliminate the activity of galactose-1-phosphate uridylyltransferase. A shortage of this enzyme prevents cells from processing galactose obtained from the diet. As a result, galactose-1-phosphate and related compounds can build up to toxic levels in the body. The accumulation of these substances damages tissues and organs, leading to the serious medical problems associated with classic galactosemia.

Most changes in the GALT gene alter single protein building blocks (amino acids) used to build galactose-1-phosphate uridylyltransferase. The most common GALT mutation in Caucasian (white) Europeans and North Americans replaces the amino acid glutamine with the amino acid arginine at position 188 in the enzyme (written as Gln188Arg). Another mutation occurs almost exclusively in people of African descent. This genetic change substitutes the amino acid leucine for the amino acid serine at position 135 (written as Ser135Leu).

A particular GALT mutation called the Duarte variant results in a form of galactosemia with less serious complications than the classic type. This mutation replaces the amino acid asparagine with the amino acid aspartic acid at protein position 314 (written as Asn314Asp). The Duarte variant reduces but does not eliminate the activity of galactose-1-phosphate uridylyltransferase. The signs and symptoms associated with this variant tend to be milder because the enzyme retains 5 percent to 20 percent of its normal activity.

Where is the GALT gene located?

Cytogenetic Location: 9p13

Molecular Location on chromosome 9: base pairs 34,646,588 to 34,650,597

The GALT gene is located on the short (p) arm of chromosome 9 at position 13.

The GALT gene is located on the short (p) arm of chromosome 9 at position 13.

More precisely, the GALT gene is located from base pair 34,646,588 to base pair 34,650,597 on chromosome 9.

See How do geneticists indicate the location of a gene? ( in the Handbook.

Where can I find additional information about GALT?

You and your healthcare professional may find the following resources about GALT helpful.

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

What other names do people use for the GALT gene or gene products?

  • Gal-1-P uridylyltransferase
  • Galactosephosphate Uridylyltransferase
  • UDP Galactose Pyrophosphorylase
  • UTP:alpha-D-hexose-1-phosphate uridylyltransferase
  • UTP-Hexose-1-Phosphate Uridylyltransferase

See How are genetic conditions and genes named? ( in the Handbook.

What glossary definitions help with understanding GALT?

acids ; amino acid ; arginine ; asparagine ; aspartic acid ; enzyme ; galactose ; gene ; glucose ; glutamine ; glycolipid ; leucine ; mutation ; phosphate ; protein ; serine ; simple sugar ; toxic

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


  • Berry GT, Reynolds RA, Yager CT, Segal S. Extended [13C]galactose oxidation studies in patients with galactosemia. Mol Genet Metab. 2004 Jun;82(2):130-6. (
  • Bosch AM, Ijlst L, Oostheim W, Mulders J, Bakker HD, Wijburg FA, Wanders RJ, Waterham HR. Identification of novel mutations in classical galactosemia. Hum Mutat. 2005 May;25(5):502. (
  • 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. (
  • Holden HM, Rayment I, Thoden JB. Structure and function of enzymes of the Leloir pathway for galactose metabolism. J Biol Chem. 2003 Nov 7;278(45):43885-8. Epub 2003 Aug 15. Review. (
  • Leslie ND. Insights into the pathogenesis of galactosemia. Annu Rev Nutr. 2003;23:59-80. Epub 2003 Apr 9. Review. (
  • NCBI Gene (
  • 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. (
  • 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: March 23, 2015