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Genetic and Rare Diseases Information Center (GARD)

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Protein S deficiency

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Your Question

Can protein S deficiency be hereditary if my mom and dad didn't have it?  How did I end up with it?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

What causes protein S deficiency?

Protein S deficiency is usually hereditary, but may be acquired.  The hereditary form of protein S deficiency is caused by a mutation in a gene called PROS1.  This condition is inherited in an autosomal dominant manner, which means that an individual who inherits only one mutated copy of PROS1 has an increased chance of developing symptoms of this disease.  Individuals who inherit one mutated copy of the PROS1 gene are said to be heterozygotes while those that inherit two mutated copies of the PROS1 gene are called homozygotes.  Blood clots (thrombosis) may occur in both heterozygotes and homozygotes; however, homozygotes may develop a severe form of thrombosis called purpura fulminans. Purpura fulminans involves severe clotting throughout much of the body and is a life-threatening condition.

Rarely, protein S deficiency is acquired, meaning it develops as a result of another condition such as liver disease or vitamin K deficiency.[1]

Last updated: 10/26/2012

Can protein S deficiency be hereditary if my parents did not have it?

Protein S deficiency can be hereditary if an affected individual's parents do not have symptoms of this disease.  Some individuals with this condition never develop symptoms; in fact, approximately 20-40% of individuals with protein S deficiency never develop a clot.[1]  This means it is possible for a parent of an affected individual to have protein S deficiency without showing signs of the condition.  Though a parent with protein S deficiency may not have symptoms, they still have a chance of passing the conditon to offspring.
Last updated: 10/26/2012