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Protein S deficiency

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Protein S deficiency is a disorder that causes abnormal blood clotting. When someone bleeds, the blood begins a complicated series of rapid chemical reactions involving proteins called blood coagulation factors to stop the bleeding.  Other proteins in the blood, such as protein S, usually regulate these chemical reactions to prevent excessive clotting. When protein S is missing (deficient), clotting may not be regulated normally and affected individuals have an increased risk of forming a blood clot called a thrombosis.  People at risk to have protein S deficiency are those with an individual or family history of multiple blood clots in the veins.  Treatment may include taking medication known as blood thinners to decrease the chance of developing a blood clot.[1]
Last updated: 3/4/2013


  1. Congenital protein C or S deficiency. MedlinePlus. February 2012; Accessed 3/4/2013.
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Basic Information

  • Genetics Home Reference (GHR) contains information on Protein S deficiency. This website is maintained by the National Library of Medicine.
  • The National Heart, Lung, and Blood Institute (NHLBI) can provide information on this topic. You can reach them by calling 301-592-8573 or by E-mail at
  • provides information on protein S deficiency written by a person who has the condition. This site addresses lifestyle issues, frequently asked questions, and more.
  • The National Hemophilia Foundation has an information page on clotting disorders, including protein S deficiency. Click on the National Hemophilia Foundation link to view this page.

In Depth Information

  • Medscape Reference provides information on this topic. Click on the link to view this information. You may need to register to view the medical textbook, but registration is free.
  • The Online Mendelian Inheritance in Man (OMIM) is an catalog of human genes and genetic disorders. Each entry has a summary of related medical articles. It is meant for health care professionals and researchers. OMIM is maintained by Johns Hopkins University School of Medicine. 
  • PubMed is a searchable database of medical literature and lists journal articles that discuss Protein S deficiency. Click on the link to view a sample search on this topic.