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


Reviewed May 2010

What is the official name of the LCT gene?

The official name of this gene is “lactase.”

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

What is the normal function of the LCT gene?

The LCT gene provides instructions for making an enzyme called lactase. This enzyme helps to digest lactose, a sugar found in milk and other dairy products.

Lactase is produced by cells that line the walls of the small intestine. These cells, called intestinal epithelial cells, have finger-like projections called microvilli that absorb nutrients from food as it passes through the intestine so they can be absorbed into the bloodstream. Based on their appearance, groups of these microvilli are known collectively as the brush border. Lactase functions at the brush border to break down lactose into smaller sugars called glucose and galactose for absorption.

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

lactose intolerance - caused by mutations in the LCT gene

At least nine LCT gene mutations cause congenital lactase deficiency, also called congenital alactasia. In this disorder, infants are unable to break down lactose (lactose intolerance) in breast milk or formula. The LCT gene mutations change single protein building blocks (amino acids) in the lactase enzyme or result in an enzyme that is abnormally short. The mutations are believed to interfere with the function of the lactase enzyme, leading to undigested lactose in the small intestine and causing severe diarrhea.

Lactose intolerance in adulthood is caused by gradually decreasing activity (expression) of the LCT gene after infancy, which occurs in most humans.

Where is the LCT gene located?

Cytogenetic Location: 2q21

Molecular Location on chromosome 2: base pairs 135,787,845 to 135,837,180

(Homo sapiens Annotation Release 107, GRCh38.p2) (NCBI (

The LCT gene is located on the long (q) arm of chromosome 2 at position 21.

The LCT gene is located on the long (q) arm of chromosome 2 at position 21.

More precisely, the LCT gene is located from base pair 135,787,845 to base pair 135,837,180 on chromosome 2.

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

Where can I find additional information about LCT?

You and your healthcare professional may find the following resources about LCT 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 LCT gene or gene products?

  • LAC
  • lactase-glycosylceramidase
  • lactase-phlorizin hydrolase
  • lactase-phlorizin hydrolase-1
  • lactase-phlorizin hydrolase preproprotein
  • LPH
  • LPH1

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

What glossary definitions help with understanding LCT?

acids ; brush border ; congenital ; deficiency ; enzyme ; epithelial ; galactose ; gene ; glucose ; hydrolase ; intestine ; microvilli ; protein

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


  • Järvelä I, Torniainen S, Kolho KL. Molecular genetics of human lactase deficiencies. Ann Med. 2009;41(8):568-75. doi: 10.1080/07853890903121033. Review. (
  • NCBI Gene (
  • Robayo-Torres CC, Nichols BL. Molecular differentiation of congenital lactase deficiency from adult-type hypolactasia. Nutr Rev. 2007 Feb;65(2):95-8. Review. (
  • Torniainen S, Freddara R, Routi T, Gijsbers C, Catassi C, Höglund P, Savilahti E, Järvelä I. Four novel mutations in the lactase gene (LCT) underlying congenital lactase deficiency (CLD). BMC Gastroenterol. 2009 Jan 22;9:8. doi: 10.1186/1471-230X-9-8. (


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: May 2010
Published: February 1, 2016