This polymorphism is also known as Factor V HR2, H1299R, His1299Arg (due to the resulting change from Histidine to Arginine in the protein) and A4070G (due to the allele being G instead of A).
Research shows that is related to the more commonly known "Factor V Leiden" mutation rs6025 .
"Factor V Leiden is present in 5% to 7% of the general population and 20% to 40% of individuals with venous thrombosis. The factor V R2 polymorphism is associated with decreased levels of factor V and it significantly increases risk of venous thrombosis in individuals who are heterozygous for the factor V Leiden mutation. Coexistence of the R2 polymorphism rs1800595 with factor V Leiden rs6025 increases the risk for venous thrombosis approximately to a 16-fold increased risk. The average age of the first thrombotic event is six years younger in individuals who are heterozygous for both factor V Leiden and the R2 polymorphism than in those with factor V Leiden alone. The R2 polymorphism is common in the general population, with one copy (heterozygous) in 10% of individuals. Among patients with venous thrombosis, approximately 12% are heterozygous for the R2 polymorphism." labcorp
"Factor V HR2 Allele, DNA Mutation Analysis is useful in patients who are carriers of Factor V Mutation (Leiden). Coinheritance of Factor V Mutation (Leiden) is associated with a 3-4-fold increased risk of venous thrombosis compared to inheritance of Factor V Mutation (Leiden) alone." http://www.questdiagnostics.com/testcenter/TestDetail.action?ntc=17902
"Phenotypic homozygous activated protein C resistance associated with compound heterozygosity for Arg506Gln (Factor V Leiden) and His1299Arg substitutions in Factor V." http://onlinelibrary.wiley.com/doi/10.1046/j.1365-2141.1997.3993213.x/pdf
"Coinheritance of the HR2 Haplotype in the Factor V Gene Confers an Increased Risk of Venous Thromboembolism to Carriers of Factor V R506Q (Factor V Leiden)." http://www.bloodjournal.org/content/94/9/3062?sso-checked=1
Table 1: R2 Haplotype SNPs. http://th.schattauer.de/de/contents/archive/issue/special/manuscript/8580/download.html
