Adult lactose digestion

Lactase is the enzyme that digests lactose, the sugar in milk. Most mammals lose it after weaning, but a variant near the LCT gene keeps it switched on into adulthood in many people.

Possible results

Likely lactose intolerant. You don't carry the variant that keeps the lactase enzyme switched on, so your ability to digest lactose (the sugar in milk) tends to fade after childhood. Dairy can then cause bloating, gas or stomach upset, which is what lactose intolerance is. Lactose-free milk and hard cheeses are usually easier to handle, and this is the most common pattern worldwide.

Lactase persistent. You inherited one copy of the variant that keeps the lactase enzyme working into adulthood. Lactase digests the sugar in milk, so you can most likely enjoy dairy without the bloating or upset that lactose intolerance causes.

Lactase persistent. You have two copies of the variant that keeps the lactase enzyme switched on for life. Your body keeps making plenty of lactase, so you can digest milk and dairy comfortably as an adult.

Evidence & sources

Across global populations, about 23% of people carry two copies of this variant, and about 44% carry none.

This variant appears in 3 published genetic studies: PubMed 29875488 · PubMed 34648354 · PubMed 37277652.

Common questions

What does the MCM6 gene do for lactose digestion? The lactase enzyme itself is made by the LCT gene, but a control switch sitting inside the neighboring MCM6 gene decides whether LCT stays on in adulthood. The variant tested here, rs4988235, is that switch. The T version keeps lactase switched on so you can digest the sugar in milk, while the C version lets it fade after childhood, which is the usual cause of adult lactose intolerance.

Does the CC genotype mean I am definitely lactose intolerant? Not always. A CC result means you lack the common European persistence variant, so lactase most likely faded after childhood and dairy may cause bloating or gas. But some people, especially of African or Middle Eastern descent, stay lactase persistent through different variants this test does not read, and tolerance also depends on gut bacteria and how much dairy you eat at once. Treat it as a strong hint, not a diagnosis.

Which rs4988235 genotype is lactose intolerant? For this European variant, CC is the genotype linked to lactase non-persistence and typical adult lactose intolerance, while CT and TT keep the lactase enzyme switched on so milk is usually digested comfortably. Your own genotype and its meaning are shown in the possible results above.

Related

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