SNP Shot: Genomic Insights

Lactose intolerance occurs when someone has difficulty digesting lactose, a sugar present in milk and other dairy products. Typically, lactose is broken down by the enzyme lactase, produced in the small intestine. Lactase deficiency can stem from both genetic and non-genetic factors.

Congenital lactase deficiency, or congenital alactasia, is a condition where infants cannot digest lactose from breast milk or formula, leading to severe diarrhea. Untreated infants may suffer from severe dehydration and weight loss, necessitating lactose-free formula.

In adults, lactose intolerance often arises from decreased lactase production after infancy, known as lactase nonpersistence. Consuming lactose-containing dairy can cause symptoms such as abdominal pain, bloating, gas, nausea, and diarrhea, typically appearing 30 minutes to 2 hours after consumption.

Many individuals with lactase nonpersistence retain some lactase activity, allowing them to tolerate small amounts of lactose without symptoms. Fresh milk is often problematic, while fermented dairy products like cheese or yogurt, which have reduced lactose content due to fermentation, are usually better tolerated.

Inheritance:

Congenital lactase deficiency follows an autosomal recessive inheritance pattern. This means an individual must inherit two copies of a mutated LCT gene (one from each parent) to develop the condition. Parents, carrying one copy of the mutated gene, are usually asymptomatic.

The ability to digest lactose into adulthood depends on the inherited variants within the regulatory element of the MCM6 gene. Variants that promote continued lactase production are autosomal dominant; inheriting just one copy is sufficient to maintain lactase production. Those who do not inherit these variants from either parent will experience lactase nonpersistence and varying degrees of lactose intolerance.