The JAK-2 V617F-mutation, a transversion mutation at nucleotide 1849 of JAK2, results in a valine-to-phenylalanine substitution at codon 617 and is associated with an increased risk of venous thrombosis via endothelial over-expression of the von Willebrand factor and p-selectin. The gene discussed is JAK2; the disease is Venous thrombosis.