URL of this page: https://medlineplus.gov/genetics/gene/lct/

LCT gene


Normal Function

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.

Health Conditions Related to Genetic Changes

Lactose intolerance

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.

More About This Health Condition

Other Names for This Gene

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

Additional Information & Resources

Tests Listed in the Genetic Testing Registry

Scientific Articles on PubMed

Catalog of Genes and Diseases from OMIM

Gene and Variant Databases


  • Jarvela I, Torniainen S, Kolho KL. Molecular genetics of human lactase deficiencies. Ann Med. 2009;41(8):568-75. doi: 10.1080/07853890903121033. Citation on PubMed
  • Robayo-Torres CC, Nichols BL. Molecular differentiation of congenital lactase deficiency from adult-type hypolactasia. Nutr Rev. 2007 Feb;65(2):95-8. doi: 10.1111/j.1753-4887.2007.tb00286.x. Citation on PubMed
  • Torniainen S, Freddara R, Routi T, Gijsbers C, Catassi C, Hoglund P, Savilahti E, Jarvela 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. Citation on PubMed or Free article on PubMed Central

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.