Susceptibility to migraine results from an adaptation of humans to the harsh climate of the northern hemisphere.
Another mischief to put on the account of evolution. In a study published in Plos Genetics, genetic researchers have shown that one of the genes associated with migraine probably results from a gradual adaptation to cold. A kind of side effect of evolution.
The culprit is called TRPM8. This gene, present on the surface of peripheral sensory neurons (present on the skin or in the mouth), codes for a receptor sensitive to both cold and menthol. However, this gene has a variant, resulting from a point mutation, which is known to be related to migraine. The genome-wide studies show an overrepresentation of this mutation in migraine patients.
By looking at this mutation of the cold receptors, the researchers found extreme geographical differences: only 5% of the population have the mutation in Nigeria, against 88% of the Finns. By compiling the data from the 1000 Genomes project, they showed that this frequency of distribution was organized according to a latitude gradient: the more a region to the north, the more the mutated version of TRPM8 is frequent.
The last 50,000 years have seen Homo sapiens leave Africa to colonize Europe. Thermal shock assured, especially as it was a glacial period. The France of that time, for example, resembled the current Siberia. Cold resistance was therefore an issue of life and death, capable of exerting enormous selective pressure.
This mutation would be an adaptation to the cold, which would have started 26,000 years ago and would have stabilized at the approach of Antiquity, between 8,000 and 3,000 years before our era. Individuals carrying the TRPM8 mutation had to have a more efficient heat regulation system, in exchange for more migraines. At the evolutionary level, the game was well worth the candle — at least until the invention of central heating.
“It’s probably the first time we’ve shown the adaptation to the environment of a sensory receptor gene,” enthuses geneticist Mark Shriver (UPenn), who was not involved in the study, in the columns of New Scientist.
The mechanism linking cold sensibility and migraine is not well understood. For example, it’s known that cold can cause headaches, the reasons why are not too clear. Studies are underway to try to treat migraine with TRPM8 receptor antagonists.