Mutations in the prothrombin gene and the factor V gene are associated with cerebral-vein thrombosis. The use of oral contraceptives is also strongly and independently associated with the disorder. The presence of both the prothrombin-gene mutation and oral-contraceptive use raises the risk of cerebral-vein thrombosis further.

It has long been thought that an individual thrombotic tendency increases the risk of myocardial infarction, especially in young adults. Several “prothrombotic” genetic factors that may influence the individual thrombotic risk have been identified. To investigate the association between the risk of myocardial infarction at a young age and genetic factors thought to be associated with an increased tendency to thrombosis (the polymorphisms 4G/5G of the PAI-1 gene, PIA1/PIA2 of the platelet glycoprotein IIIa, C3550T of the platelet glycoprotein Ib gene, G10976A of the factor VII gene, C677T of the methylenetetrahydrofolate reductase gene, G1691A of the factor V gene, and G20210A of the prothrombin gene), we performed a case-control study evaluating 200 survivors (185 men, 15 women) of myocardial infarction who had experienced the event before the age of 45 years and 200 healthy subjects with a negative exercise test, individually matched for sex, age, and geographic origin with the cases. The presence of the PIA2 polymorphic allele was the only prothrombotic genetic factor associated with the risk of myocardial infarction at a young age. The odds ratio for carriers of the PIA2 allele compared with those of the PIA1 allele was 1.84 (95% confidence intervals (CI) 1.12 to 3.03). There was a significant interaction between the presence of the PIA2 allele and smoking: with their simultaneous presence, 46% (95% confidence intervals 11% to 81%) of premature myocardial infarctions were attributable to the interaction between the two factors. In conclusion, carrying the PIA2 polymorphic allele of platelet glycoprotein IIIa was the only genetic prothrombotic factor associated with the risk of developing myocardial infarction at a young age. The clinical expression of this genetic predisposition seems to be enhanced by smoking.