Lactose-intolerantie genotypering

Beschrijving

People who develop complaints after drinking milk can be divided into two groups. One part may have an intolerance to the milk sugar lactose that is present in the milk and another part may have an allergy to the cow’s milk protein.

Lactose intolerance involves a deficiency of the enzyme lactase, which is formed in the small intestine. Lactose is made up of the molecules glucose and galactose and lactase cuts the bonds between these molecules and in this way lactose is digested in the body. In the Netherlands, the lactase enzyme is absent in 5 percent of adults of Western descent. If lactose is not broken down in the intestine, complaints such as diarrhea and nausea can occur.

A milk allergy is caused by an intolerance to the protein casein. Beta-casein type A2 is formed in the human body. This protein has a protective effect and is present in breast milk. Milk from certain types of cows contains type A1 casein and the human immune system can see this as a foreign substance – while it is very similar to type 2 and does not provoke an immune response. The immune system will overreact, causing an allergic reaction. A cow’s milk protein allergy occurs in 2.8 percent of infants worldwide.

With this research we focus on demonstrating or ruling out congenital lactose intolerance or whether it is a lactase deficiency due to damage to the intestine. In many cases, a cow’s milk allergy can be detected via a blood or skin test. If you suspect a cow’s milk allergy, consult your doctor.

Background lactose intolerance

What makes the concept of lactose intolerance confusing is that from an evolutionary perspective, a decrease in lactase production in the small intestine is normal. Humans – just like any other mammal – stop drinking milk at a certain age. This means that it is no longer necessary to produce the enzyme lactase in the body to break down the lactose. Peoples who started consuming milk from animals have retained the enzyme and the body has adapted genetically. The advent of dairy farming about 10,000 years ago led to the transmission of the variant of the gene and people continued to produce lactase in old age. Because the consumption of dairy products by older children and adults in Western countries is considered normal, the lack of lactase production is seen as an abnormality. While in Europe about 10 to 20 percent of the population cannot tolerate milk sugar, in Southeast Asia this is almost 100 percent of the population.

Primary or secondary lactose intolerance

It is therefore debatable what should be considered ‘normal’ with regard to the level of lactase activity in humans. Thousands of years ago, declining lactase activity at a young age was not a disease, but genetically normal. Due to a genetic change (mutation) in the lactase gene, different variations of the gene arose and there were people who could also digest lactose later in life. This was considered beneficial and as a result, people who developed complaints after taking dairy products later in life were labeled as lactose intolerant.

When lactose activity is absent or decreases at a young age (lactase non-persistent), this is called primary lactose intolerance. It is congenital and that person will never tolerate lactose and must be on a lactose free diet. People who have the variation in the gene that causes lactase activity to remain high later in life (lactase persistent) may develop complaints after consuming milk. This is then referred to as secondary lactose intolerance and the intestinal wall is often damaged by underlying diseases. If symptoms disappear after a lactose-free diet, it is likely that the person has secondary lactose intolerance. If the complaints do not disappear after a lactose-free diet, then lactose intolerance has been ruled out and other tests (for example for celiac disease) should be done.

The test

By taking buccal mucosa and isolating DNA from these cells, the real-time PCR method can be used to investigate whether someone has a congenital lactose intolerance or whether the person can still produce lactase, but has complaints due to a damaged intestinal wall. This test is called genotyping and the advantage over the H2 breath test is that this test is much less time-consuming and the sampling is very simple. This can provide a definitive answer as to whether it concerns primary or secondary lactose intolerance, allowing a treatment plan to be drawn up in a much more targeted manner.