Lactase non-persistence (LNP) is as an autosomal recessive trait leading to down-regulation of lactase activity in the intestinal mucosa and to maldigestion of lactose. The down-regulation is genetically determined and a mutation has occurred that has made part of mankind tolerate milk (lactase persistence).
Milk and some dairy products contain lactose, a disaccharide hydrolysed by the enzyme lactase-phlorizin hydrolase to glucose and galactose in the brush border of the small intestine. Digestion of lactose is mediated by lactase, an enzyme uniquely expressed in epithelial cells of the small intestine. In mammals, lactase expression initiates before birth, remains high during the nursing period and then progressively declines after weaning, resulting in lactase non-persistence.
Inability to digest lactose due to lactase non-persistence is a common trait in adult mammals, with the exception of certain human populations that exhibit lactase persistence.
The first genetic variant associated with lactase non-persistence, a one-base polymorphism C > T -13910 (rs 4988234) upstream of the lactase encoding gene on chromosome 2, was identified in 2002.
In Northern Europe lactase persistence is common, which allows the majority of the population to drink milk without any consequences. However, in populations where the frequency of the lactase persistent genotype is rather low the consumption of milk may cause complaints in the digestive tract.
Lactase non-persistence (adult-type hypolactasia)
