Protein C deficiency is a rare genetic disorder characterized by a deficiency of protein C, which is a natural anticoagulant. This means it helps to prevent the blood from clumping together clotting too much. There is a mild form in which affected individuals are at risk for developing blood clots, particularly a type of blood clot called deep vein thrombosis. This is a clot that forms in the legs. Although very rare, there is a severe form that is present at birth congenital and can potentially cause widespread small clots in the body and life-threatening complications in infancy. Protein C deficiency is caused by alterations mutations in the PROC gene. The milder form is caused by an alteration in one PROC gene and is inherited in an autosomal dominant manner. The severe form is caused by an alteration in both PROC genes and is inherited in an autosomal recessive manner.