Protein S is a glycoprotein essential in the regulation of blood coagulation. Familial protein deficiency increases risk venous thromboembolism approximately 2- to 11-fold. Herein, we report this disorder six members Vietnamese family among which three had thromboembolism, and other were asymptomatic. The levels ranged from 10.1% 24%, but did not identify any PROS1 mutation. In one patient, rar...