People with protein C deficiency have too little protein C in their bloodstream. Because of this, they’re more likely to experience symptoms of a blood clot, such as pain and swelling in the legs or chest pain from clogged arteries in the lungs (pulmonary embolism). Protein C deficiency can be congenital or acquired. Congenital cases are caused by mutations in genes that control how much protein C is made by your body. Acquired cases happen when your liver doesn’t produce enough protein C because it’s damaged by other diseases (such as sepsis) or drugs.