The presence of G to A transition in the 30 upstream untranslated region of the prothrombin gene at the nucleotide locus 20210 may play a regulatory role in gene expression.   2  In 1996, for the first time, Poort et al.   2  published the result of their research regarding a common genetic variation (G20210A) in the prothrombin gene that was associated with higher prothrombin levels and with an increased risk for venous thrombosis. This evidence concerns the gene F2 and Venous thrombosis.