OMIM: #223100
Gen: LCT
Locus: 2q21


Lactose intolerance (Adult type hypolactasia) is the inability to digest and absorb lactose (the sugar in milk), resulting in gastrointestinal symptoms when milk or products containing milk are drunk or eaten. In order for lactose to be absorbed from the intestine and into the body, it must first be split into glucose and galactose. The enzyme that splits lactose into glucose and galactose is called lactase, and it is located on the surface of the cells that line the small intestine. Lactose intolerance is caused by reduced or absent activity of lactase that prevents the splitting of lactose (lactase deficiency or hypolactasia).

Diagnosis of lactose intolerance
Usually, lactose intolerance was diagnosed by ingestion of pure lactose and measurement of hydrogen in the breath. Unfortunately, the hydrogen test lasts several hours and leads to strong abdominal symptoms in lactose intolerant patients.

Recently, the genetic cause for the lactose intolerance was discovered. At the location -13910 before the lactase gene (LCT) there is a polymorphism, which determines the quantity of lactase produced. By testing the LCT genotype the genetic disposition for lactose intolerance can be determined .

LCT -13910 genotypes

Genotype Frequency Commentary
LCT -13910  TT 40% No genetic disposition to lactose intolerance
LCT -13910  TC 45% No genetic disposition to lactose intolerance
LCT -13910  CC 15% Genetic disposition for lactose intolerance

Indications for testing
Symptoms of lactose intolerance, such as abdominal pain, diarrhea, flatulence (passing gas), after ingestion of milk or dairy products.

Treatment of lactose intolerance
The most obvious means of treating lactose intolerance is by reducing the amount of lactose in the diet. Fortunately, most people who are lactose intolerant can tolerate small or even moderate amounts of lactose. It often takes only elimination of the major milk-containing products to obtain sufficient relief from their symptoms. For individuals who are intolerant to even small amounts of lactose, the dietary restrictions become more severe and any purchased product containing milk should be avoided.

  • Hogenauer C, Hammer HF, Mellitzer K, Renner W, Krejs GJ, Toplak H. Evaluation of a new DNA test compared with the lactose hydrogen breath test for the diagnosis of lactase non-persistence. Eur J Gastroenterol Hepatol. 2005;17:371-6.