DNA Lactose Intolerance Test

Lactose Digestion

Lactose, the sugar found in dairy products, is digested by the lactase enzyme. Lactase is produced in the small intestine and is responsible for breaking down lactose into two smaller and more readily absorbable sugars – glucose and galactose. Most mammals produce high levels of the lactase enzyme as infants, and then lactase production decreases after weaning. However, due to our reliance on dairy products as a food source, many humans now have lactase persistence, where the lactase enzyme is continually produced throughout adulthood. These lactase persistent individuals can continue to digest lactose throughout their lifetime. Lactase persistence occurs in more than 75% of Caucasians around the world, and approximately 95% of people of Northern European ancestry. Other ethnicities have a much lower proportion of lactase persistence (e.g. approximately 50% of Mexicans, only 10% of Asians and less than 5% of Native Americans). 

What is Lactose Intolerance?

Lactose intolerance occurs due to decreased production of the lactase enzyme. Undigested lactose builds up in the large intestine, resulting in the growth of gas-producing gut bacteria, which contribute to the symptoms of lactose intolerance, including bloating, flatulence, diarrhea, nausea and abdominal pain. This may be a temporary lactase reduction (e.g. after surgery or short-term illness) or a permanent reduction, due to a lifelong disease (e.g. cystic fibrosis) or due to genetic variation. The genetic test offered here identifies individuals that carry a genetic variation that permanently reduces lactase production. Lactose intolerance differs from a dairy allergy, as individuals who are allergic to dairy will have an immune response (an allergic reaction) against milk proteins, whereas lactose intolerance is a digestive disorder.

What Genetic Variations Distinguish between Lactose Intolerance and Lactase Persistence?

There are five common genetic changes that allow for lactase persistence. These genetic changes occur in a regulatory element in the MCM6 gene. The MCM6 gene encodes a protein that controls the production of other proteins, including lactase, encoded by the nearby LCT gene. The genetic changes in the MCM6 gene result in the increased production of lactase, and first appeared when humans became more reliant on dairy as a food source. The changes have been strongly selected for in populations that consume more dairy products.

The LCT (lactase) and MCM6 (regulatory protein) genes are located on chromosome two, one of the autosomal chromosomes. Autosomal chromosomes are inherited in pairs – one from each parent. If an individual inherits two copies of the wild type MCM6 gene, they will be lactose intolerant in adulthood and will pass this wild type gene to the next generation. If an individual inherits two copies of the variant MCM6 gene, they will have lactase persistence and will pass this lactase persistence to the next generation. If an individual has one copy of a wild type MCM6 gene and one copy of a variant MCM6 gene, they usually have lactase persistence (although there may be some lactose sensitivity). This pattern of inheritance is referred to as autosomal dominant as only one copy of the variant gene is required to provide the lactase persistence.

DNA Testing for Lactose Intolerance and Lactase Persistence

A simple DNA test can be completed to determine which versions of the MCM6 gene an individual has inherited. The DNA test provided by this laboratory examines these five markers that are associated with lactose intolerance (wild type) or lactase persistence (variant).

• rs41525747, -13907C>G
• rs4988235, -13910C>T
• rs41380347, -13915T>G
• rs145946881, -14010G>C
• rs182549, -22018G>A

Recommended Links:

Ranciaro A et al. (2014). Genetic Origins of Lactase Persistence and the Spread of Pastoralism in Africa. The American Journal of Human Genetics 94: 496–510.

Itan Y, Powell A, Beaumont MA, Burger J, Thomas MG (2009). The Origins of Lactase Persistence in Europe. PLoS Comput Biol 5(8): e1000491.

Gerbault P et al. (2011). Evolution of lactase persistence: an example of human niche construction. Phil. Trans. R. Soc. B. 366: 863–877.

Swallow DM (2003). Genetics of Lactase Persistence and Lactose Intolerance. Annu. Rev. Genet. 37: 197–219.