October 03, 2003
Genetics of Lactase Intolerance
Annual Review of Genetics
Posted online as a Review In Advance on 22 April 2003.
Genetics of Lactase Persistence and Lactose Intolerance
Dallas M. Swallow
Abstract The enzyme lactase that is located in the villus enterocytes of the small intestine is responsible for digestion of lactose in milk. Lactase activity is high and vital during infancy, but in most mammals, including most humans, lactase activity declines after the weaning phase. In other healthy humans, lactase activity persists at a high level throughout adult life, enabling them to digest lactose as adults. This dominantly inherited genetic trait is known as lactase persistence. The distribution of these different lactase phenotypes in human populations is highly variable and is controlled by a polymorphic element cis-acting to the lactase gene. A putative causal nucleotide change has been identified and occurs on the background of a very extended haplotype that is frequent in Northern Europeans, where lactase persistence is frequent . This single nucleotide polymorphism is located 14 kb upstream from the start of transcription of lactase in an intron of the adjacent gene MCM6. This change does not, however, explain all the variation in lactase expression.
Posted by Dienekes at October 3, 2003 10:16 PM | PermaLinkAn interesting question is whether the African cattle-raising tribes such as the Dinka who are typically lactose tolerant have the same genetic mutation as Northern Europeans, or whether it arose separately. Does anybody know yet?
Posted by: Steve Sailer at October 5, 2003 07:24 PMI dont know it for sure, but if you think that in southern Europe the lactose tolerance is not that high, I would guess that they developed it through local selection like many blood factors (sickle cell anaemie for example, and some characteristics of the immun system) without to much genetic influence of Europeans.
This feature is coming up when people lived under extreme conditions when many people of the population suffered from malnutrition and died or had not enough healthy kids.
Just thinking about the nutrition of the Dinka and Massai and you know how important milk can be for the survival especially of nomads.
The same process occured in Northern Europe too were the vitamins and energy level was even more critical.