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LCT gene
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Gene

LCT gene

The LCT gene provides instructions for the enzyme lactase, which is necessary for the digestion of lactose, the primary sugar found in milk.

Normal Function

The LCT gene provides instructions for making the enzyme lactase. This enzyme is produced by intestinal epithelial cells that line the small intestine. These cells feature small, finger-like projections called microvilli, which form the brush border. Lactase functions at the brush border to break down lactose into smaller sugars, glucose and galactose, which can then be absorbed into the bloodstream.

Health Conditions Related to Genetic Changes

Lactose intolerance

Rarely, variants in the LCT gene cause congenital lactase deficiency (also known as congenital alactasia). In this condition, infants are unable to break down lactose in breast milk or formula. These genetic variants can alter the amino acid sequence of the lactase enzyme or cause the production of an abnormally short enzyme. These changes interfere with the processing and function of lactase, leading to undigested lactose in the small intestine and causing severe diarrhea.

Lactose intolerance in adulthood can also result from lactase nonpersistence, which is the gradually decreasing expression of the LCT gene after infancy. This is a common occurrence in humans and can also have non-genetic causes.

Other Names for This Gene

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

Frequently Asked Questions

Most adults with lactase nonpersistence retain residual lactase activity or have gut microflora that can ferment small quantities of lactose without triggering symptoms. Many can comfortably digest up to 12 grams of lactose per day (roughly the amount in one cup of milk), particularly when consumed with other foods. Naturally aged hard cheeses (such as cheddar and parmesan) and yogurt containing live active cultures have very low lactose levels and are generally well tolerated.
Strict elimination of dairy products increases the risk of inadequate calcium and vitamin D intake, which can impair bone mineral accrual in adolescents and accelerate osteopenia or osteoporosis in older adults. Individuals strictly avoiding dairy should undergo periodic dietary reviews to ensure adequate micronutrient intake through fortified plant milks, canned bone-in fish, leafy greens, or targeted dietary supplements.
Congenital lactase deficiency is a rare, severe, autosomal recessive disorder caused by structural mutations in the LCT gene, presenting in the first days of life with intractable watery diarrhea, severe dehydration, and malnutrition upon ingestion of breast milk or standard formula. In contrast, common adult lactose intolerance stems from lactase nonpersistence, a normal developmental decline in LCT gene expression regulated by an adjacent enhancer region within the MCM6 gene, which typically develops after early childhood.
Diagnosis is suspected when severe neonatal diarrhea rapidly resolves within 24 to 48 hours of replacing breast milk or standard formula with a lactose-free formula. Confirmation is achieved primarily through targeted genetic sequencing of the LCT gene. Stool tests during acute symptoms typically reveal an acidic stool pH (below 5.5) and the presence of reducing substances, confirming carbohydrate malabsorption.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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