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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 several other dairy products.

Lactase is produced by some of the cells that line the walls of the small intestine. These cells, called intestinal epithelial cells, have small, finger-like projections called microvilli. As food passes through the intestine, the microvilli collect nutrients so they can be absorbed into the bloodstream. 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

Rarely, LCT gene variants (also called mutations) cause congenital lactase deficiency.  In this disorder (also known as congenital alactasia), infants are unable to break down lactose in breast milk or formula. Infants who are unable to process lactose are considered lactose intolerant.

Variants in the LCT gene can change single protein building blocks (amino acids) in the lactase enzyme. In some cases, variants cause cells to create lactase enzymes that are abnormally short. The variants are believed to interfere with the processing and function of the lactase enzyme, leading to undigested lactose in the small intestine and causing severe diarrhea.

Lactose intolerance in adulthood can also be caused by the gradually decreasing activity (expression) of the LCT gene after infancy. This condition is known as lactase nonpersistence, and it occurs in most humans. It can also have non-genetic causes.

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


  • Diekmann L, Pfeiffer K, Naim HY. Congenital lactose intolerance is triggered by severe mutations on both alleles of the lactase gene. BMC Gastroenterol. 2015 Mar 21;15:36. doi: 10.1186/s12876-015-0261-y. Citation on PubMed
  • Fazeli W, Kaczmarek S, Kirschstein M, Santer R. A novel mutation within the lactase gene (LCT): the first report of congenital lactase deficiency diagnosed in Central Europe. BMC Gastroenterol. 2015 Jul 28;15:90. doi: 10.1186/s12876-015-0316-0. Citation on PubMed
  • Heine RG, AlRefaee F, Bachina P, De Leon JC, Geng L, Gong S, Madrazo JA, Ngamphaiboon J, Ong C, Rogacion JM. Lactose intolerance and gastrointestinal cow's milk allergy in infants and children - common misconceptions revisited. World Allergy Organ J. 2017 Dec 12;10(1):41. doi: 10.1186/s40413-017-0173-0. eCollection 2017. Citation on PubMed
  • 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.