Protein S deficiency

What it is, symptoms and effects

From: MedlinePlus Genetics, National Library of Medicine

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.

In rare cases, individuals have a severe form of protein S deficiency with signs and symptoms that develop soon after birth. Affected infants typically develop a life-threatening blood clotting disorder called purpura fulminans. Purpura fulminans is characterized by the formation of blood clots within small blood vessels throughout the body. These blood clots disrupt normal blood flow and can lead to the death of tissues (necrosis). Widespread blood clotting uses up all available blood clotting proteins. As a result, the body can no longer create clots, and bleeding occurs in various parts of the body. This abnormal bleeding often appears as large, purple skin lesions. Affected individuals who survive the newborn period may experience recurrent episodes of purpura fulminans.

Causes and biological mechanisms

From: MedlinePlus Genetics, National Library of Medicine

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.

Most variants that cause protein S deficiency change single DNA building blocks (base pairs) in the PROS1 gene. These gene variants change the amount of functional protein S. Individuals with protein S deficiency may not have enough functional protein S to inactivate clotting proteins, which increases the risk of developing blood clots.

Some cases of protein S deficiency are acquired, which means they do not appear to be caused by gene variants. Causes of acquired protein S deficiency include vitamin K deficiency, liver disease, and kidney disorders.

Inheritance and family implications

From: MedlinePlus Genetics, National Library of Medicine

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.

In rare cases, a person has a variant in both copies of the PROS1 gene. This is typical of individuals with the severe form of protein S deficiency that develops in infancy. This form of protein S deficiency is inherited in an autosomal recessive pattern, which means both copies of the gene in each cell must have a variant to cause the disorder.

Acquired protein S deficiency is not inherited and typically occurs in people with no history of the condition in their family.

How common is it?

From: MedlinePlus Genetics, National Library of Medicine

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

The severe form of protein S deficiency that develops in infancy is rare, although its exact prevalence is unknown.

Which doctor should you see?

The suggested department for discussing Protein S deficiency is Clinical Genetics, with a clinical geneticist as the relevant type of clinician. Paediatrician (children) or physician (adults), with clinical geneticist referral.

This is an editorial referral starting point. The appropriate clinic depends on the person’s age, symptoms, previous diagnosis and local services. The first clinician can decide whether another specialty or a team is needed; a department label does not confirm the diagnosis.

How to prepare for an assessment

Bring a short timeline of the main symptoms: when they first appeared, whether they are constant or episodic, what seems to change them, and how they affect daily activities. Include previous reports, discharge summaries, current medicines and supplements, allergies, and any relevant family history. A dated record is more useful than trying to match every feature in an online article.

Ask the clinician what is already established and what remains uncertain. If a test is suggested, ask what question it answers, what its limitations are and how the result would change the next step. The information here is not an instruction to arrange every possible test. In children, bring growth, developmental and school information if it is relevant to the concern.

• Does the exact genetic or chromosome finding explain the observed features?
• Would a genetic counsellor help the family understand the result?
• Which organ-specific assessments are appropriate for this particular diagnosis?

Treatment discussions and follow-up

The material gathered for this draft does not provide a complete condition-specific treatment pathway for Protein S deficiency. That gap does not mean that treatment is unavailable. A clinician needs to establish the diagnosis and review current guidance before recommending medicines, procedures, rehabilitation or other support.

Before leaving the appointment, clarify the next review date, who will communicate results, and whom to contact if the situation changes. Discuss difficulties with sleep, work, school, mobility, eating or emotional wellbeing when these are relevant. Practical support may require coordination between the treating clinician and other services.

The collected references do not establish a complete prevention or long-term outlook section for this entry. Missing information should not be interpreted as proof that prevention is impossible or that a particular outcome is inevitable. Ask what is known for the exact subtype, stage and personal circumstances, and which uncertainties remain.

When to seek emergency help

Severe breathing difficulty, collapse, new stroke-like symptoms, a seizure that is prolonged or repeated without recovery, uncontrolled major bleeding, or an immediate risk of self-harm require emergency help. In India, call 112 or reach the nearest emergency department. This is a general, non-exhaustive warning list; it is not a condition-specific triage tool.