Alternative Names
Lactase deficiency; milk intolerance; disaccharidase deficiency; dairy product intolerance; adult hypolactasia
Symptoms & Characteristics
Lactose is a sugar found in milk and foods made with milk (dairy products). In order for lactose to be converted to energy, lactose needs to get broken down into two simpler sugars during digestion. This process requires an enzyme called lactase.
The enzyme lactase is produced at high levels during infancy and early childhood when dairy products like breast-milk are a primary source of nutrition. Then, naturally, lactase levels decline into adulthood and with it the ability to digest large quantities of milk and dairy products without side effects. When lactase levels decline, lactose cannot be digested in the small intestine and instead, gets fermented by bacteria in the lower digestive system causing gas, diarrhea, as well as abdominal pain and swelling. People with low lactase levels in adulthood are called lactose intolerant.
Some people produce lactase into adulthood and can continue to consume dairy products without negative side effects. These people are called lactase persistent.
Treatment
Lactose intolerance is not serious. Eating fewer foods with lactose, or using pills or drops that help digest lactose may be effective. Calcium supplements may also be recommended.
If someone notices or experiences any of the signs or symptoms common to lactose intolerance, it is important to see a doctor.
How Common Is It?
People of African and Asian ancestry as well as people descended from native populations of Australia, North America and South America are more likely to be lactose intolerant.
People of European, eastern African, and southwestern Asian ancestry are more likely to be lactase persistent.
Genetics & Inheritance
The enzyme lactase is produced by the LCT gene on chromosome 2 at the location of q21. The LCT gene is typically only "turned on" (active) for the first couple of years of life in humans (and all mammals). The "turning on" and "turning off" of the LCT gene is controlled by a gene close to it called the MCM6 gene.
We all have two copies of the MCM6 gene.
- People with lactose intolerance, have both copies of the LCT gene "turned off," and therefore, have two normal copies of the MCM6 gene.
- People with lactase persistence, have a variation in at least one copy of the MCM6 gene causing at least one copy of the LCT gene to remain "turned on." Different variations are common to different ethnic backgrounds.
Other yet to be identified or adequately classified genes may also contribute to lactose intolerance/lactase persistence.
Other genetic conditions that cause either abnormalities in the production of lactase or the digestion of lactose include congenital lactase deficiency and congenital lactose intolerance.
Congenital lactase deficiency (CLD) is a severe gastrointestinal disorder. Symptoms begin in early infancy. Congenital lactase deficiency is caused by mutations in the LCT gene and is inherited in an autosomal recessive manner. This condition is rare and is mostly found in Finland.
Congenital lactose intolerance also presents in the early infancy. Symptoms may include vomiting, failure to grow, dehydration, as well as kidney and liver problems. The genetics of congenital lactose intolerance are currently unknown.
Genetic Testing
Clinical genetic testing for well documented genetic variations that result in lactose intolerance/lactase persistence may be available through an in person genetic consultation for people who are considered at risk. Use our find a genetic professional directory to locate a trained genetic professional in your area.
Informational genetic testing for additional genetic variations that may be associated with lactose intolerance/lactase persistance in Caucasians of Northern European descent is available online as part of a whole genome scan. Whole genome scanning involves analyzing thousands of small genetic variations called SNPs that are related to a number of different health conditions.
- At this point, many genetic professionals do not consider this testing clinically useful or medically relevant, but for informational purposes only. Go to the Tests tab to link to the best providers, compare providers and read provider reviews.
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