Protein S deficiency is a disorder that increases the risk of developing blood clots. People with protein S deficiency are at risk of developing a type of clot called a deep vein thrombosis (DVT) that occurs in the deep veins of the arms or legs. A DVT can travel through the bloodstream and lodge in the lungs, causing a life-threatening clot called a pulmonary embolism (PE). Both DVTs and PEs are a type of venous thromboembolism, a general term for blood clots that form in a vein. Factors such as age, surgery, immobility, or pregnancy can increase the risk of clotting in people with protein S deficiency. In addition, people who have protein S deficiency and another inherited blood clotting disorder may have a higher risk of developing blood clots. Venous thromboembolism occurs in approximately fifty to sixty percent of people with protein S deficiency.

Protein S deficiency can be caused by variants (also called mutations) in the PROS1 gene. This gene provides instructions for making protein S, which is found in the bloodstream and is important for the control of blood clotting. Protein S helps block the activity of (inactivate) certain proteins that promote the formation of blood clots.

Protein S deficiency is estimated to occur in approximately 1 in 500 individuals.

Protein S deficiency is typically inherited in an autosomal dominant pattern, which means one copy of the altered gene in each cell is sufficient to increase the risk of clotting.

Published Date: April 30, 2024
Published By: National Institutes of Health