People with lactose intolerance have reduced tolerability as an adult for the milk sugar (lactose) contained in milk and milk products. While this is still tolerated in children's years, the lactose-digesting enzyme, the lactase, is lost in adulthood. In January, a Finnish research group published its findings on the search for the causes of lactose intolerance (Enattah NS et al .: Nature Genetics, January 14, 2002, published online ahead of print).
Distribution in different groups of peoples
Lactose intolerance differs widely in different peoples: while it is a rare phenomenon in northern Europe, accounting for 5% of the population, almost all the inhabitants of Southeast Asia are affected, so it is less a disease than 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 those of hundreds of other subjects from all over the world. It turned out that there are no mutations in the genome of the affected person (information section) for the lactase enzyme. However, in one area in front of this gene, a mutation was found that had all those affected and thus seems to be responsible for the "disease".
The researchers showed that this mutation lies in a section that probably regulates whether the lactase enzyme is produced or not. While this section is functional for lactose intolerant, it is defective in people who tolerate lactose all their lives: perhaps nature has not intended that man should be able to consume milk throughout his life.
Mutation probably due to evolution
This observation goes along with the researchers' calculations that this mutation should have originated in humans about ten to twelve thousand years ago. This is about the time when production and consumption of milk spread in Europe.
Apparently, the individuals who tolerated milk throughout their lives had an advantage over the lactose intolerant, so that northern Europe today is populated almost exclusively by milk-contracting people.
Consequences for medicine
The discovery of this mutation has an important consequence for diagnostics: whereas until now a lactose intolerance had to be determined by extensive tests, a relatively simple genetic test, for example from a saliva sample, could provide a clear diagnosis in the future.