In fact protein S deficiency is the most consistently observed coagulation abnormality observed in HIV-infected patients, with a reported prevalence ranging from a 27% to a 76%, with a 12% of those patients having a venous thromboembolism.29–32 PS deficiency in HIV-positive patients is probably multi-factorial and the frequency of this alteration/deficiency has led to an extensive pursuit of potential mechanism. This evidence concerns the gene PROS1 and venous thromboembolism.