Protein S deficiency

Protein S deficiency is a genetic disorder that makes one liable to the formation of abnormal clots in blood vessels. It was in the year 1984 when Protein S deficiency was first described.1

Protein s deficiency


Protein S is a just a specific protein in your body that prevents the formation of excess clots in your bloodstream. Thus, it keeps the normal process of blood clotting under check and avoids the risk of abnormal clot formation. It works along with other protein of similar action called protein C and needs the vitamin K for its production.

What Protein S actually does is that it stops the action of factor V and VIII – the two activated proteins involved in blood clotting process. In case your blood has decreased levels of protein S, there is uncontrolled action of these two clotting proteins that remain activated and your blood clotting tendency may go up.1

Protein S deficiency

Protein S deficiency can be:

  • Present at birth - inherited from parents to the child
  • Present after birth - acquired as seen in
    • Vitamin K deficiency
    • With certain medications like Warfarin (an anti-coagulant)
    • With infection
    • Disseminated intravascular coagulation
    • Acute thrombosis (blood clot formation)
    • Warfarin
    • Nephrotic syndrome
    • Antiphospholipid antibodies
    • Liver disease2, 3

The Genetics behind Protein S deficiency simplified:

A specific gene responsible for production of Protein S is passed onto you from your parents. In fact two normal copies of this gene – one from mother, another from your father are normally passed onto you. In case of inherited Protein S deficiency, either one abnormal gene & one normal gene or two abnormal Protein S genes are passed onto you. On this basis, the patients are divided into two groups:

  • Heterozygous Protein S deficiency: The person, who has 1 defective protein S gene inherited either from father or mother, is known as heterozygous for protein S deficiency.
  • Homozygous Protein S deficiency: The person, who has 2 defected protein S genes – one defective gene from father and other defective gene from mother, is known as homozygous for protein S deficiency.
    • Heterozygous Protein S gene individuals are at a slightly higher risk of getting a thrombosis (blood clots) than those individuals who do not have the abnormal genes.
    • Homozygous individuals have a much greater and potentially fatal risk.

In case you have any other risk factor (as mentioned below), the risk of getting blood clots is further increased:

  • Pregnancy
  • Estrogen therapy
  • Oral birth control pills
  • Surgery
  • Prolonged restriction of movement (immobilization or being bed ridden due to some long-standing illness)
  • Increased age
  • Infection
  • Other coagulation abnormalities like Factor V Leiden. 4, 5

Types of Protein S Deficiency

Protein S exists in two forms in our blood – a free form and a bound form, bound with a specific protein. Together they constitute the total Protein S level. There are 3 types of Protein S deficiency:

  • Type I: defect in the quantity of Protein S due to genetic abnormality causing less production of this protein. Both free form and bound form of Protein S are reduced.
  • Type II: defect in the function of the Protein S.
  • Type III: Only free form of the Protein S is reduced. The total Protein S level however remains normal.1

How Common is Protein S Deficiency

Protein S deficiency has been seen to occur in almost 1 in 20,000 people.6

Symptoms of Protein S Deficiency

  • In case of Homozygous Protein S Deficiency, there may occur severe and fatal neonatal purpura fulminans (diffuse purple discoloration of the skin due to the bleeding underneath, medically known as purpura). There is also the possibility of massive venous thrombosis (numerous blood clots in veins of legs, lungs or brain).
  • In case of Heterozygous Protein S Deficiency, there is also a risk for developing thrombosis.
  • Postphlebitic syndrome: This is a chronic complication of abnormal blood clots. It includes pain, swelling, ulceration of skin and induration in the lower limbs.

Diagnosing Protein S Deficiency

Being a silent abnormality, the best and the only method for diagnosing the deficiency of Protein S is by a blood test. This blood test will let you know about how much Protein S is in your blood. You would get the results of this test within two to three days. The diagnosis of protein S is suspected in those individuals who have a history of blood clots and also in those who have a family history of abnormal blood clots.2


You should test yourself for Protein S Deficiency in case:

  • You have a family history of thrombophilia or blood clotting
  • You have a history of transient ischemic attacks
  • You have a history of premature stroke
  • You have a history of two or three miscarriages or babies born dead4

Treatment for Protein S Deficiency

Unless your blood begins to clot while you are a known case of Protein S deficiency, you do not need any treatment unless your blood starts to clot.

In case you do have or ever have had a blood clot while you are a known case of Protein S deficiency, your treatment would be anticoagulant therapy. The duration of treatment ranges from 3 months to whole life. The anticoagulants include:

  • Heparin
  • Low-molecular-weight heparins
  • Warfarin

In case of life threatening blood clots in patients with Protein S deficiency, the fresh frozen plasma (FFP) usage can be utterly helpful.1, 4

If Protein S Deficiency is left untreated

In comparison to the normal individuals, the people suffering from inherited form of Protein S deficiency have about a 2 to 11 times increased risk for developing a Deep Venous Thrombosis or a Pulmonary Embolism.7 According to some recent studies, the protein C and protein S deficiencies are associated with an increased risk of arterial blood clot formation (leading to heart attacks and stroke). 1

Prognosis for people with Protein S Deficiency

  • Inherited Protein S deficiency: As discussed earlier, there is an increased risk of thrombus formation in homozygous Protein S deficiency as well as in many of those having heterozygous Protein S deficiency. Nevertheless, there is a chance that some individuals who are heterozygous for the abnormal Protein S gene will never ever develop a blood clot.
  • Hence, the prognosis depends on how early the diagnosis is made, how effective are the measures to prevent the blood clot formation and how effectively is the current blood clot(s) treated.
  • In case of the acquired Protein S deficiency, the prognosis will depend on how cruel the underlying cause is.
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