A common haplotype for the 677T thermolabile variant of the 5,10‐methylenetetrahydrofolate reductase gene in thrombophilic patients and controls

The common polymorphic transition 677C>T in the 5,10‐methylenetetrahydrofolate reductase (MTHFR) gene causes a thermolabile enzyme variant. This variant is associated with moderate hyperhomocysteinemia, a risk factor for vascular disease and thrombophilia. Up to now, it remained unclear if the thermolabile MTHFR variant either directly predisposes to vascular disease, or if 677T is only a genetic marker for another causative genetic alteration in cis . Aim of this study was to characterize the genetic background of 677T‐alleles by haplotype analysis. We analyzed 25 individuals of German descent homozygous for 677T: nine young patients, who had suffered from thromboembolic events, and 16 healthy controls. The results of this study demonstrate that the 677T alleles are associated with a common haplotype most likely due to a founder effect and that the 677T haplotype was the same in the healthy and the thrombophilic German subjects. © 2002 Wiley‐Liss, Inc.