Lactose intolerance, DNA-test

Lactose is found in milk and dairy products. Lactose consists of two simple sugars: galactose and glucose. Lactase is an enzyme that breaks lactose in the gut down into galactose and glucose, which are absorbed from the gut into the bloodstream.

A lack of the lactase enzyme that breaks down lactose causes a metabolic disorder called lactose intolerance. In lactose intolerance, the breaking down and absorption of lactose is affected. In this condition, untreated lactose passes from the small intestine to the large intestine, where bacteria break the lactose down and hydrogen gas and lactic acid are produced. In addition, lactose in the gut attracts water through osmosis.

In early humans, the lactase enzyme broke down the lactose in the mother’s milk, but the enzyme was no longer necessary as an adult, and its loss in adulthood was normal. A mutation has taken place in the gene of the enzyme so that the enzyme no longer disappears when maturing into an adult. Approximately 18% of Finns have the original gene, and their lactase enzyme disappears in adulthood. In some people, the lack of the gene does not cause any symptoms.

The lack of the lactase enzyme can also be caused by damage and irritation of the small intestine. Such damage to the small intestine can be caused by coeliac disease, chronic intestinal infection, Crohn’s disease, irritable bowel syndrome, or excessive alcohol consumption, for example. This is known as secondary lactase deficiency. Coeliac disease is the prime disease causing lactase deficiency, and it should be excluded as the cause of lactose intolerance.

When should lactose intolerance be measured?

Typically, the symptoms occur within 30–120 minutes of ingesting dairy products. The subject may have symptoms suggesting lactose intolerance:

• Stomach pain
• Abdominal swelling
• Flatulence
• Diarrhoea
• Stomach cramps

What does a lactose intolerance DNA test measure?

The lactose intolerance DNA test (B-Lakt-D) finds out if the subject has a genetic lactase deficiency. The gene test cannot exclude other secondary factors affecting lactose tolerance, such as coeliac disease or gut infections.

The results indicate the genotype and its more detailed interpretation: genotype C/C means primary lactase deficiency, which suggests lactose intolerance. Genotypes T/C and T/T are not linked to lactase deficiency, meaning that the symptoms are caused by a condition other than lactose intolerance. The intensity of the symptoms cannot be determined based on the result of the gene test.