Lactose intolerance

Why take a genetic test for lactose intolerance

1. Lactose is a sugar present in milk and milk products. The enzyme lactase is responsible for its breakdown in the small intestine into simple sugars (glucose and galactose), which are further absorbed. Lack of lactase, from primary or secondary causes, leads to symptoms of lactose intolerance (2).
2. The onset of the disease is usually inconspicuous and accompanied by non-specific symptoms that escape attention; Lactose intolerance becomes progressive in many patients only during adolescence or adulthood (3). Just because you haven't noticed any symptoms yet doesn't mean you don't have an intolerance.
3. The effect of the genetic test will not affect the associated diseases, so you do not have to worry about a false negative or false positive result. Genome testing is performed non-invasively (just take a blood sample) for interested people of all age categories, and it is enough to take the test once in a lifetime, because the human genome does not change over time.
4. The genetic test will allow to recognize the so-called the primary form of lactose intolerance, when the lactase enzyme deficiency is hereditary, and distinguish it from the so-called secondary intolerance, when there are other causes of intestinal damage (e.g. intestinal inflammation, celiac disease or gluten intolerance), which subsequently also cause lactose intolerance (4).

When is it appropriate to take a lactose intolerance test?

Lactose intolerance is a condition when the small intestine stops producing enough of the enzyme lactase, which digests lactose. The undigested lactose then travels to the large intestine, where it interacts with the bacteria of the intestinal microbiome. The symptoms of lactose intolerance are the result of fermentation of undigested lactose by bacteria in the large intestine (5).

Indigestion of lactose leads to the penetration of liquid into the lumen of the intestine, which is the cause of the so-called osmotic diarrhea. During the fermentation of unabsorbed lactose, bacteria in the large intestine produce gases (hydrogen, carbon dioxide and methane) and short-chain fatty acids, while lactose is hydrolysed into monosaccharides. This leads to another rush of fluid into the intestine, causing these symptoms:

• bloating,
• flatulence,
• diarrhea,
• abdominal cramps,
• nausea (6).

These symptoms usually appear 30 minutes to 2 hours after eating a dairy product or drinking milk (7). If you observe them for a long time, we recommend taking a test for lactose intolerance. The severity of the symptoms depends on the amount of lactose consumed, the function of the lactase enzyme and the transit time of the dairy food through the small intestine (8). In addition to these (typical) symptoms, headaches, muscle and joint pain, mouth ulcers, urinary problems and loss of concentration also appear (9).

What else you should know about lactose intolerance before you take the test

In addition to primary lactose intolerance, which is the most common, there is also the so-called secondary, which arises as a result of infectious, inflammatory or other diseases. These cause damage to the intestinal mucosa, which leads to a secondary lactase enzyme deficiency (10). The classic cases leading to secondary lactose intolerance are gastroenteritis (inflammation of the stomach and intestines), celiac disease, Crohn's disease and ulcerative colitis; the risk also increases with chemotherapy and the use of antibiotics.

ATTENTION: Watch out for overlap of symptoms and mutually influenced occurrence, especially in case of lactose intolerance and celiac disease (11). Most celiac patients with significant damage to the intestinal mucosa have secondary lactose intolerance due to reduced lactase activity in the brush border of the enterocyte (12). Patients with lactose intolerance generally have a high incidence of celiac disease. In an Italian study, celiac disease was diagnosed in 24% of patients with lactose intolerance, and in many, lactase deficiency was the only manifestation of celiac disease (13). In addition to the lactose intolerance test, we also recommend a celiac disease test.

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About lactose intolerance

Lactose intolerance (hyplolactasia) is caused by reduced activity of the enzyme lactase, which breaks down lactose in the small intestine. Lactose is one of the basic milk sugars. It is also the main source of carbohydrates in the nutrition of chicks. Intolerance is manifested by the inability to digest this sugar and also by a reduced capacity for its absorption. The symptoms of lactose intolerance are often associated with lactose malabsorption, which is the result of a low level of the lactase enzyme in the small intestine.

In the small intestine, lactose is broken down by the enzyme lactase (β-galactosidase) into two monosaccharides: glucose and galactose. In the European population, lactose intolerance is associated with two polymorphisms of the lactase enzyme gene: -13910 T > C and -22018 A > G. Genetic testing reveals a genetically determined primary lactase deficiency and should only be used in selected populations. This test can be used in populations where the -13910 T/C polymorphism is associated with lactase persistence (14). A common genetic test for lactose intolerance detects four gene polymorphisms:

• genetic variant -13910 T > C corresponds to almost 100% lactase persistence in Europeans,
• other three genetic variants have a similar effect and are more common in non-European populations (15).