Five thrombophilia-related polymorphisms, Factor V Leiden (F5 G1691A), prothrombin (F2 G20210A), methylenetetrahydrofolate reductase (MTHFR C677T and MTHFR A1298C), and Plasminogen Activator Inhibitor-1 (PAI-1) 4G/5G, were examined for allele and genotype frequencies, Hardy–Weinberg equilibrium testing, pairwise linkage disequilibrium (D′ and r2), and power analysis. The gene discussed is MTHFR; the disease is Rare hereditary thrombophilia.