Factor V Leiden, prothrombin 20210A, methylenetetrahydrofolate reductase 677T, and population genetics.

Thrombosis results from the interaction between predisposing genetic polymorphisms and acquired risk factors. Two of the main prothrombotic alleles, Factor V (FV) Leiden and prothrombin 20210A, are only encountered among European populations. They are estimated to have arisen about 21,000-34,000 years ago as founding mutations after the evolutionary divergence of Caucasians from Asians, and have been subsequently dispersed by the Neolithic migrations. These polymorphisms may have developed by means of genetic drift or natural selection by possibly conferring a reduced risk of bleeding. Of note, FV Leiden is nearly absent in the Basques, a European population of pre-Neolithic individualization. The C677T mutation of the methylenetetrahydrofolate reductase gene may induce hyperhomocysteinemia and could slightly increase the risk of arterial or venous thrombosis and pregnancy loss in individuals with folic acid deficiency. Through a selective phenomenon, the frequency of the mutation may parallel the intake of this vitamin within populations. Hence, this allele is underrepresented in Sub-Saharan Africa, Indonesia, and in the Inuits and a positive North to South gradient has been described in Europe. Thus, these three inherited prothrombotic polymorphisms represent interesting tools for population genetics studies.