Mutation Most Likely Triggers Lactose Intolerance

As adults, people with lactose intolerance have a reduced tolerance for the milk sugar (lactose) found in milk and milk products. While this is still tolerated in childhood, the lactose-digesting enzyme, lactase, is lost in adulthood. A group of Finnish researchers published their findings in January in search of the causes of lactose intolerance (Enattah N.S. et al: Nature Genetics, January 14, 2002, published online ahead of print).

Prevalence in different ethnic groups

Lactose intolerance varies in prevalence among different peoples: while it is a rare phenomenon in northern Europe, where it affects 5% of the population, it affects almost all inhabitants of southeast Asia, so it must be considered less as a disease and more as a genetic trait.

Lactose intolerance is genetically normal

The Finnish researchers analyzed the genetic information of nine Finnish families in which lactose intolerance occurred, as well as that of hundreds of other subjects from around the world. It was found that there were no mutations in the actual gene (information section) for the lactase enzyme in the genetic material of those affected. However, a mutation was found in a region upstream of this gene, which all affected persons had and which thus seems to be responsible for the “disease”.

The researchers showed that this mutation is located in a section that probably regulates whether the lactase enzyme is produced or not. While this section is functional in the lactose intolerant, it is defective in people who tolerate lactose all their lives: it is possible that nature did not intend for humans to be able to consume milk all their lives.

Mutation probably evolutionary

This observation goes hand in hand with the researchers’ calculation that this mutation should have arisen in humans about ten to twelve thousand years ago. This is about the time when the production and consumption of milk became widespread in Europe.

Apparently, the individuals who were able to tolerate milk throughout their lives as a result of the mutation had an advantage over those who were lactose intolerant, so that nowadays northern Europe is populated almost exclusively by milk-tolerant people.

Consequences for medicine

The discovery of this mutation has an important consequence for diagnostics: whereas in the past lactose intolerance had to be detected by elaborate tests, in the future a relatively simple genetic test, for example from a saliva sample, could provide an unambiguous diagnosis.