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Mappings

MONDO

MONDO:0013791 thrombophilia due to protein S deficiency, autosomal recessive Not Yet Curated

The severe biallelic form (THPH6, OMIM #614514) is curated within this entry (AR inheritance block, Neonatal Purpura Fulminans, homozygous-patient evidence). Mapped at narrowMatch so the AR MONDO leaf is anchored and retired from the curation queue while the AD leaf remains the primary disease_term.

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Inheritance

1

Autosomal dominant inheritance HP:0000006

The common hereditary protein S deficiency (THPH5) is autosomal dominant with incomplete penetrance; about half of heterozygous carriers remain asymptomatic.

Autosomal dominant inheritance Penetrance: INCOMPLETE

Show evidence (2 references)

PMID:40429442 SUPPORT Human Clinical

"Congenital PS deficiency follows an autosomal dominant inheritance pattern."

States the autosomal dominant inheritance pattern of congenital protein S deficiency.

PMID:40429442 SUPPORT Human Clinical

"Approximately 50% of heterozygous individuals develop VTE, while the remaining half remain asymptomatic throughout their lives."

Documents the incomplete penetrance of the heterozygous form.

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Subtypes

4

Type I (quantitative deficiency)

PROS1 hgnc:9456

Quantitative deficiency: reduced total protein S antigen, reduced free protein S antigen, and reduced protein S functional activity. One of the two most commonly encountered phenotypes clinically.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"type 1 (quantitative deficiency), characterized by low levels of total protein S (TPS) and free protein S (FPS), along with reduced protein S activity"

ISTH classification defining Type I quantitative protein S deficiency.

Type II (qualitative/dysfunctional)

PROS1 hgnc:9456

Qualitative (functional) deficiency: normal total and free protein S antigen but decreased protein S functional activity, indicating a dysfunctional protein. The rarest of the three subtypes; the Japanese founder variant PROS1 p.Lys196Glu ("PS Tokushima") is a classic example.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"type 2 (functional deficiency, also known as type 2b), characterized by normal levels of TPS and FPS, but with decreased protein S activity, indicating a functional defect"

ISTH classification defining Type II qualitative protein S deficiency.

Type III (selective free-protein-S deficiency)

PROS1 hgnc:9456

Selective free-protein-S deficiency: normal total protein S antigen but reduced free protein S antigen and reduced activity, reflecting an abnormal partitioning between the free and C4b-binding-protein-bound fractions. Along with Type I, one of the two most common phenotypes.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"type 3 (selective free protein s deficiency, also known as type 2a), characterized by normal TPS levels but reduced FPS and PS activity"

ISTH classification defining Type III selective free-protein-S deficiency.

Severe Autosomal Recessive (Biallelic) Deficiency

PROS1 hgnc:9456

The severe biallelic (homozygous or compound heterozygous) form (THPH6, OMIM #614514, MONDO:0013791). In contrast to the common heterozygous autosomal dominant form, near-total loss of protein S activity presents in the neonatal period with purpura fulminans - disseminated microvascular thrombosis with hemorrhagic skin necrosis - and massive venous thrombosis. This clinical AD-mild / AR-severe axis is orthogonal to the ISTH laboratory Types I/II/III above.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"a homozygous mutation presents with thrombotic events in early infancy and is often life-threatening"

Defines the severe biallelic form as an early-infancy, life-threatening entity distinct from the mild heterozygous form.

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Discussions and Knowledge Gaps

1

How much of protein S's in vivo anticoagulant effect in human hereditary deficiency is mediated through the APC-cofactor pathway versus the APC-independent TFPI-cofactor pathway, and does this partition differ across Type I/II/III subtypes and disease severity?

KNOWLEDGE GAP ps_cofactor_pathway_partition

Attached to

pathophysiology#Reduced Protein S Cofactor Activity

Protein S has two mechanistically distinct anticoagulant cofactor roles (APC and TFPI). The global Pros1-/- model shows an aPC-independent component of accelerated thrombin generation (animal_models#Global Pros1 knockout mouse (Pros1-/-)), and the p.Lys196Glu knock-in model selectively reduces APC-cofactor activity (animal_models#Protein S K196E (Tokushima) knock-in mouse). But the K196E model cannot resolve the partition, because protein S TFPI-cofactor activity is not detectable in mouse plasma; the human claim of preserved TFPI-cofactor activity in K196E rests on human/biochemical data. The relative contribution of the two pathways in human hereditary deficiency, and its dependence on ISTH Type I/II/III subtype and severity, is unresolved.

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Pathophysiology

5

Reduced Protein S Cofactor Activity

Loss-of-function PROS1 variants reduce the level or function of protein S, a hepatocyte-synthesized vitamin K-dependent glycoprotein that is a non-enzymatic cofactor for activated protein C (APC) in the inactivation of factors Va and VIIIa and, independently, for tissue factor pathway inhibitor (TFPI). Reduced free/functional protein S diminishes this anticoagulant cofactor activity.

hepatocyte CL:0000182

PROS1 hgnc:9456

Genetic context PROS1 hgnc:9456 variant_origin: GERMLINE functional_impact_category: LOSS_OF_FUNCTION

Loss-of-function PROS1 variants. Zygosity is deliberately not recorded on this node because it is what separates the two clinical forms this entry models: heterozygous variants give the common, incompletely penetrant autosomal dominant deficiency, and biallelic variants give the severe neonatal recessive form (Severe AR subtype).

negative regulation of blood coagulation GO:0030195 ↓ DECREASED

APC anticoagulant cofactor (enzyme activator) activity GO:0008047 ↓ DECREASED

Animal models

Platelet-specific Pros1 knockout mouse (Pros1lox/loxPf4-Cre+) Mouse partially recapitulates Loss of platelet-derived protein S increases venous thrombus propensity by impairing its cofactor role for APC and TFPI, limiting factor X activation and thrombin generation within the growing thrombus at low shear rates. It does not increase arterial thrombosis propensity, unlike systemic human deficiency.

Global Pros1 knockout mouse (Pros1-/-) Mouse partially recapitulates Complete protein S loss produces a fulminant coagulopathy with accelerated thrombin generation, including an activated-protein-C-independent component, modeling the anticoagulant-cofactor failure of severe deficiency.

Protein S K196E (Tokushima) knock-in mouse Mouse recapitulates Reproduces a qualitative (Type II-like) defect: normal protein S antigen with selectively reduced APC-cofactor activity, and increased susceptibility to venous thrombosis.

Downstream

Unopposed Thrombin Generation and Fibrin Formation Diminished APC/TFPI cofactor activity allows sustained factor Va/VIIIa and factor Xa activity, amplifying thrombin generation.

Reduced Protein S Activity Reduced protein S cofactor function is measured directly as reduced protein S functional (APC-cofactor) activity - the diagnostic laboratory readout of this molecular defect.

Warfarin-Induced Transient Anticoagulant Depletion A deficient protein S baseline makes the transient post-warfarin fall in protein S (and protein C) activity proportionally more severe on initiation of a vitamin K antagonist.

Show evidence (3 references)

PMID:42429079 SUPPORT Human Clinical

"Protein S (PROS1) is a vitamin K-dependent plasma glycoprotein that was originally described as a non-enzymatic cofactor of activated protein C in the regulation of blood coagulation."

Establishes the causal gene and the classic non-enzymatic APC-cofactor role of protein S.

PMID:41180656 SUPPORT Human Clinical

"Protein S enhances the anticoagulant effect of protein C by serving as its cofactor; thus, deficiency in either protein leads to impaired inactivation of factors Va and VIIIa, fostering a prothrombotic state"

Directly describes the cofactor mechanism and the prothrombotic consequence of its loss.

DOI:10.1182/blood.2019003630 SUPPORT INDIRECT Model Organism

"At a low shear rate, PSplt functions as a cofactor for both activated protein C and tissue factor pathway inhibitor, thereby limiting factor X activation and thrombin generation within the growing thrombus"

Mouse-model evidence for the dual APC/TFPI cofactor mechanism of protein S in limiting thrombin generation.

Unopposed Thrombin Generation and Fibrin Formation

With natural anticoagulant down-regulation weakened, the coagulation cascade proceeds toward unchecked thrombin generation and thrombin-driven conversion of fibrinogen into an insoluble fibrin network.

platelet CL:0000233

blood coagulation GO:0007596 ↑ INCREASED fibrin clot formation GO:0072378 ↑ INCREASED

Downstream

Venous Thrombus Formation Excess thrombin and fibrin, particularly under the low-shear conditions of venous flow, drive pathological venous thrombus formation.

Disseminated Microvascular Thrombosis In severe biallelic deficiency the near-total loss of anticoagulant control drives widespread small-vessel (microvascular) fibrin thrombosis, distinct from the large-vein thrombus of the common heterozygous form.

Show evidence (2 references)

PMID:41180656 SUPPORT Human Clinical

"Protein C and protein S are vitamin K-dependent glycoproteins that function as critical anticoagulants by regulating the coagulation cascade."

Establishes protein S as a critical anticoagulant regulator whose loss releases coagulation-cascade activity.

PMID:40429442 SUPPORT Human Clinical

"The coagulation cascade, composed of intrinsic and extrinsic pathways, culminates in the activation of thrombin, which converts fibrinogen to fibrin"

Describes the thrombin-driven fibrin-formation step that this node represents.

Venous Thrombus Formation

Formation of a pathological intravascular fibrin-platelet thrombus, most often in the deep veins of the lower extremities, which may propagate or embolize to the pulmonary arteries.

platelet CL:0000233

blood coagulation, fibrin clot formation GO:0072378 ↑ INCREASED

Downstream

Deep venous thrombosis A lower-extremity deep venous thrombus is the most common clinical manifestation.

Pulmonary embolism A venous thrombus may dislodge and embolize to the pulmonary arteries.

Superficial thrombophlebitis Superficial-vein thrombosis (thrombophlebitis) is a frequent parallel venous manifestation of the same hypercoagulable state, second in frequency only to deep venous thrombosis among symptomatic carriers.

Show evidence (2 references)

PMID:40429442 SUPPORT Human Clinical

"A deficiency in PS disrupts normal coagulation control, leading to an increased risk of thrombophilia and VTE due to an excessive blood clot formation"

Directly links reduced protein S to excessive clot formation and venous thromboembolism.

PMID:40429442 SUPPORT Human Clinical

"Fibrin serves as the structural framework of the thrombus, stabilizing platelet aggregates and incorporating red blood cells."

Describes the fibrin-platelet composition of the thrombus this node represents.

Disseminated Microvascular Thrombosis

Widespread small-vessel (microvascular) fibrin thrombosis of the skin and other tissues in severe biallelic protein S deficiency, the lesion underlying neonatal purpura fulminans. Distinct from the large-vein fibrin-platelet thrombus of the common heterozygous form.

platelet CL:0000233

blood coagulation, fibrin clot formation GO:0072378 ↑ INCREASED

Downstream

Neonatal Purpura Fulminans Disseminated microvascular thrombosis produces the hemorrhagic skin necrosis of neonatal purpura fulminans.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"a homozygous mutation presents with thrombotic events in early infancy and is often life-threatening"

Establishes the severe, early-onset thrombotic process of biallelic deficiency that manifests as microvascular purpura fulminans.

Warfarin-Induced Transient Anticoagulant Depletion

Because protein S (and protein C) have short plasma half-lives relative to the procoagulant vitamin K-dependent factors, initiating a vitamin K antagonist transiently deepens the anticoagulant deficit before procoagulant factors fall, producing a brief hypercoagulable window that can precipitate microvascular skin necrosis in an already-deficient patient.

negative regulation of blood coagulation GO:0030195 ↓ DECREASED

Downstream

Warfarin-Induced Skin Necrosis The transient hypercoagulable window drives microvascular thrombosis of the skin and subcutaneous fat.

Show evidence (2 references)

PMID:9885367 SUPPORT Human Clinical

"Coumarin skin necrosis occurs almost exclusively in patients with venous thrombosis between the 3rd and 10th day after beginning anticoagulation."

Establishes the early-initiation timing window of the warfarin-induced hypercoagulable state.

PMID:24144709 SUPPORT Human Clinical

"Vitamin K antagonists decrease plasma level of vitamin K-dependent coagulation proteins, including the natural anticoagulant protein C."

Documents the vitamin K antagonist-driven fall in natural anticoagulants underlying this node.

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Pathograph

Use the checkboxes to hide or show graph categories. Hover nodes for evidence and cross-linked metadata.

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Phenotypes

6

Blood 4

Deep venous thrombosis Most common manifestation; ~74% of symptomatic carriers in the classic family series. HP:0002625

Show evidence (1 reference)

PMID:2952034 SUPPORT Human Clinical

"Most symptomatic patients had various combinations of deep venous thrombosis (74%), superficial thrombophlebitis (72%), and pulmonary embolism (38%)"

Quantifies deep venous thrombosis as the most frequent manifestation among symptomatic carriers.

Superficial thrombophlebitis ~72% of symptomatic carriers in the classic family series; second only to deep venous thrombosis. HP:0002638

Show evidence (1 reference)

PMID:2952034 SUPPORT Human Clinical

"Most symptomatic patients had various combinations of deep venous thrombosis (74%), superficial thrombophlebitis (72%), and pulmonary embolism (38%)"

Quantifies superficial thrombophlebitis frequency among symptomatic protein S-deficient patients.

Neonatal Purpura Fulminans HP:0000979

HPO has no dedicated "purpura fulminans" term; HP:0000979 Purpura is the closest bindable phenotype. The neonatal onset and severity are the cited claim here.

Show evidence (2 references)

PMID:24144709 SUPPORT Human Clinical

"We report a case of a 6-year-old girl with severe protein S deficiency due to a homozygous mutation and recurrent episodes of skin necrosis. She developed purpura fulminans at birth"

Directly reports neonatal purpura fulminans in homozygous (severe) protein S deficiency.

PMID:40429442 SUPPORT Human Clinical

"a homozygous mutation presents with thrombotic events in early infancy and is often life-threatening"

Establishes the early-infancy, life-threatening presentation of biallelic protein S deficiency.

Reduced Protein S Activity HP:0004855

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"PS functional activity assays measure the biological activity of PS by assessing its ability to function as a cofactor for APC in the inactivation of FVa and FVIIIa."

Establishes reduced protein S functional (APC-cofactor) activity as the laboratory phenotype.

Cardiovascular 1

Pulmonary embolism HP:0002204

Show evidence (1 reference)

PMID:24144709 SUPPORT Human Clinical

"She developed purpura fulminans at birth and a catheter-related venous thrombosis complicated by massive pulmonary embolism at the sixth day of life."

Documents massive pulmonary embolism in a patient with severe (homozygous) protein S deficiency.

Integument 1

Warfarin-Induced Skin Necrosis HP:0001038

Show evidence (1 reference)

PMID:9885367 SUPPORT Human Clinical

"Although protein C deficiency is the most common underlying hypercoagulable state reportedly associated with warfarin skin necrosis, very few cases have been linked to congenital protein S deficiency."

Establishes warfarin-induced skin necrosis as a recognized complication of congenital protein S deficiency.

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Genetic Associations

2

PROS1 (Loss-of-function PROS1 variants cause hereditary protein S deficiency. Heterozygous variants cause the common, incompletely penetrant autosomal dominant form (THPH5); biallelic variants cause the severe autosomal recessive neonatal form (THPH6). More than 200 distinct PROS1 variants have been reported, predominantly point mutations, including transversions producing a premature stop codon and a truncated, nonfunctional protein.)

Gene: PROS1 hgnc:9456 relationship_type: CAUSATIVE

Autosomal dominant inheritance Autosomal recessive inheritance

Show evidence (3 references)

PMID:40429442 SUPPORT Human Clinical

"Mutations in the PROS1 gene are responsible for congenital PS deficiency"

Establishes PROS1 as the causal gene for congenital protein S deficiency.

PMID:40429442 SUPPORT Human Clinical

"Over 200 different PROS1 mutations have been identified, giving rise to distinct forms of PS deficiency."

Documents the allelic heterogeneity of PROS1 variants.

PMID:40429442 SUPPORT Human Clinical

"Heterozygous mutation typically exhibit a mild PS deficiency, whereas homozygous or compound heterozygous mutations result in severe PS deficiency, which can lead to life-threatening thrombotic complications."

Establishes the dominant-mild versus biallelic-severe genotype-phenotype relationship.

F5 (Co-inheritance of the factor V Leiden variant (F5 c.1601G>A, p.Arg534Gln; legacy R506Q) is a common second thrombophilic hit in PROS1-deficient families and sharply raises thrombotic risk and lowers age at first event. Factor V Leiden was present in 29-38% of symptomatic protein S-deficient probands across two family studies; in sibships co-segregating both defects, 80% of double-carriers were symptomatic; and mean age at first thrombosis was 18.4 years in combined-defect carriers versus 32.6 years with a single defect.)

Gene: F5 hgnc:3542 relationship_type: MODIFIER

Show evidence (3 references)

PMID:8584987 SUPPORT Human Clinical

"In sibships where both abnormalities were segregating, the percentage of symptomatic individuals with both abnormalities was 80%."

Quantifies the fraction of symptomatic double-carriers when factor V Leiden co-segregates with protein S deficiency.

PMID:8584987 SUPPORT Human Clinical

"Among 16 symptomatic protein S deficient probands the prevalence of the FV Leiden mutation was high (38%)."

Documents the high factor V Leiden prevalence among symptomatic protein S-deficient probands (selection reflects familial thrombosis referral).

PMID:9607123 SUPPORT Human Clinical

"The age at first thrombosis was significantly lower (P < 0.001) in the ten propositi with a combined genetic defect (mean age 18.4 +/- 6.6 years) than in those with a single defect (mean age 32.6 +/- 10.4 years)."

Quantifies the earlier age at first thrombosis when a second defect (factor V Leiden) is co-inherited with protein C/S deficiency.

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Medical Actions

2

Long-Term Anticoagulation with Heparin-Bridged Initiation

Action: anticoagulation therapy Ontology label: Anticoagulation Therapy NCIT:C63341

Agent: warfarin CHEBI:10033 rivaroxaban CHEBI:68579

Platform: Small molecule

Anticoagulation (a vitamin K antagonist such as warfarin, or a direct oral anticoagulant such as rivaroxaban) reduces the risk of recurrent venous thromboembolism; duration is individualized to recurrence versus bleeding risk. When warfarin is used, initiation should be bridged with heparin and avoid high loading doses, because unbridged warfarin can precipitate warfarin-induced skin necrosis in protein S (or protein C) deficiency. Direct oral anticoagulants avoid this mechanism and are an alternative, including in severe deficiency with recurrent warfarin necrosis.

Mechanism Target:

INHIBITS Unopposed Thrombin Generation and Fibrin Formation — Vitamin K antagonism or direct factor Xa inhibition suppresses ongoing coagulation-cascade activation, reducing the risk of recurrent thrombosis.

BYPASSES Warfarin-Induced Transient Anticoagulant Depletion — Heparin bridging during warfarin initiation, or use of a direct oral anticoagulant instead of warfarin, avoids the transient protein C/S depletion window that can precipitate skin necrosis.

Show evidence (2 references)

PMID:24144709 SUPPORT Human Clinical

"The switch of anticoagulant therapy from warfarin to rivaroxaban, a direct inhibitor of activated factor X that does not inhibit other vitamin K-dependent proteins, resulted in the disappearance of skin necrosis at 1 year of follow-up."

Documents a direct oral anticoagulant as an effective alternative avoiding warfarin-induced skin necrosis in severe protein S deficiency.

PMID:24144709 SUPPORT Human Clinical

"Rivaroxaban may be considered as a valid anticoagulant alternative in patients with severe inherited protein S deficiency and warfarin-induced skin necrosis."

States the therapeutic recommendation for a direct oral anticoagulant in this setting.

Pregnancy Thromboprophylaxis with Low-Molecular-Weight Heparin

Action: Anticoagulation Therapy NCIT:C63341

Agent: low-molecular-weight heparin NCIT:C2578

Pregnancy is the single highest-risk window in hereditary thrombophilia. Low-molecular-weight heparin is the preferred antepartum and postpartum thromboprophylaxis because it does not cross the placenta; obstetric risk schemes (e.g., RCOG) that incorporate inherited thrombophilia guide when it is indicated. Vitamin K antagonists are generally avoided in pregnancy (and carry the additional protein S-specific skin-necrosis risk noted above).

Mechanism Target:

INHIBITS Venous Thrombus Formation — LMWH prophylaxis suppresses thrombin generation and venous thrombus formation during the high-risk peripartum period.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"potentially indicating the need for low-molecular-weight heparin prophylaxis"

Obstetric risk schemes incorporating inherited thrombophilia indicate LMWH prophylaxis in pregnancy.

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Environmental Factors

1

Estrogen-Containing Oral Contraceptive or Hormone Therapy

Exogenous estrogen physiologically lowers free protein S and supplies a "second hit" that can precipitate venous thromboembolism in a carrier of an otherwise silent hereditary protein S deficiency genotype.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"vitamin K deficiency, liver disease, DIC, nephrotic syndrome due to protein S loss, pregnancy, oral contraceptives, hormone replacement therapy"

Lists oral contraceptives and hormone replacement therapy among the acquired states that lower protein S levels.

Mechanism Target:

EXACERBATES Venous Thrombus Formation — Estrogen exposure amplifies venous thrombosis risk on a background of reduced protein S.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"vitamin K deficiency, liver disease, warfarin therapy, pregnancy and hormonal therapy, nephrotic syndrome, severe infections or inflammatory states (downregulation of protein S synthesis), and FV Leiden causes false low PS levels"

Documents pregnancy and hormonal therapy as states that lower protein S levels, amplifying thrombotic risk.

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Biochemical Markers

2

Free Protein S Antigen (Decreased)

Context: Free protein S antigen measures the functionally active, non-C4BP-bound fraction (~40% of total) and is the most reliable screening measurement: it is reduced in Types I and III. Interpretation is sex- and age-stratified (women have lower free and total protein S than men) and results are repeated in stable conditions off pregnancy, hormonal therapy, acute thrombosis, and anticoagulation.

Pathograph Readouts

Readout Of Reduced Protein S Cofactor Activity Negative Diagnostic

Lower free protein S antigen tracks with lower anticoagulant cofactor activity; the free fraction is the functionally active pool.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"The free form is functionally active."

Establishes free protein S antigen as the functionally active fraction that reports on cofactor activity.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"Notably, women generally have lower total and free protein S levels than men. Total PS levels increase with age, particularly in women, due to hormonal variations, whereas free PS levels remain stable over time."

Establishes the sex- and age-dependence of protein S antigen levels, which stratifies reference-range interpretation.

Total Protein S Antigen (Decreased or normal)

Context: Total protein S antigen (free plus C4BP-bound) is reduced in Type I (quantitative) deficiency but normal in Types II and III, so it detects Type I but misses the qualitative and selective-free subtypes.

Pathograph Readouts

Readout Of Reduced Protein S Cofactor Activity Negative Diagnostic

A low total protein S antigen indicates quantitative (Type I) deficiency; a normal total with reduced activity indicates Type II/III.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"type 1 (quantitative deficiency), characterized by low levels of total protein S (TPS) and free protein S (FPS), along with reduced protein S activity"

Total protein S antigen is reduced in Type I deficiency, the readout distinguishing quantitative from qualitative subtypes.

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Diagnosis

2

Protein S Deficiency: Free Antigen and Functional Activity Assay

Protein S functional activity is assessed by its ability to act as an APC cofactor in inactivating factors Va and VIIIa; free and total protein S antigen are measured separately by immunoassay. Free protein S antigen is the most reliable screen because it reflects the functionally active, non-C4BP-bound fraction; total antigen detects Type I but not Type II or III. Reference ranges are sex-, age-, and pregnancy-dependent (women have lower total and free protein S than men; total protein S rises with age), so results must be interpreted against stratified ranges and repeated outside pregnancy, hormonal therapy, acute thrombosis, and anticoagulation. Factor V Leiden can cause falsely low functional protein S in older clot-based assays.

coagulation study NCIT:C62662

Results: Reduced free and/or total protein S antigen, or reduced protein S functional activity with normal antigen (Type II/III).

Show evidence (2 references)

PMID:40429442 SUPPORT Human Clinical

"PS functional activity assays measure the biological activity of PS by assessing its ability to function as a cofactor for APC in the inactivation of FVa and FVIIIa."

Directly describes the functional-cofactor basis of the protein S activity assay.

PMID:40429442 SUPPORT Human Clinical

"Notably, women generally have lower total and free protein S levels than men. Total PS levels increase with age, particularly in women, due to hormonal variations, whereas free PS levels remain stable over time."

Establishes the sex- and age-dependence of protein S reference ranges.

PROS1 Molecular Genetic Testing

After a functional/antigen abnormality is confirmed and acquired causes are excluded, PROS1 sequencing confirms hereditary deficiency; the ISTH maintains a registry of documented PROS1 mutations. Because many acquired and physiologic states lower protein S, laboratory testing must be repeated in stable conditions before a hereditary diagnosis is made. (Note: the exact ISTH-SSC criterion of two abnormal results >=4 weeks apart, and large-deletion detection by MLPA, are standard practice but are not stated in this entry's cited review and are therefore not asserted here with a snippet.)

PROS1 genetic testing NCIT:C15709

Results: A pathogenic or likely-pathogenic PROS1 variant confirms hereditary protein S deficiency.

Show evidence (2 references)

PMID:40429442 SUPPORT Human Clinical

"After ruling out acquired causes and if a hereditary deficiency is suspected, PROS1 genetic testing should be performed."

Establishes PROS1 sequencing as the confirmatory molecular test after acquired causes are excluded.

PMID:40429442 SUPPORT Human Clinical

"Thus, repeat testing in stable conditions is recommended."

Establishes the requirement to repeat testing in stable conditions before a hereditary diagnosis.

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Prevalence

3

General population (mild congenital deficiency)

Point Prevalence 200.0 per 100,000 >1 in 1,000

Source phrasing "the estimated incidence of mild congenital PS deficiency is approximately 1 in 500 individuals"; 1 in 500 = 200 per 100,000.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"The estimated incidence of mild congenital PS deficiency is approximately 1 in 500 individuals, while severe PS deficiency is exceedingly rare, with an unknown prevalence due to diagnostic challenges"

Population estimate for mild congenital protein S deficiency; severe biallelic form is exceedingly rare.

Healthy blood donors (familial protein S deficiency)

Point Prevalence 30.0–130.0 per 100,000 1–9 per 10,000

Source phrasing "the prevalence of familial PS deficiency ranged between 0.03% and 0.13%" among healthy blood donors (30-130 per 100,000). Rises to 3-5% among patients selected for recurrent thrombosis or family history.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"In a study of healthy blood donors, the prevalence of familial PS deficiency ranged between 0.03% and 0.13%. However, the prevalence increases significantly among patients with recurrent thrombosis or a family history of thrombosis, ranging from 3% to 5%"

Blood-donor screening prevalence and its increase in thrombosis-referral cohorts.

General Japanese population

Point Prevalence 480.0–630.0 per 100,000 >1 in 1,000

Source phrasing "estimated from 0.48% to 0.63% in the general Japanese population" (480-630 per 100,000); higher than in the US/Europe, partly due to the Japan-specific PROS1 p.Lys196Glu ("PS Tokushima") founder variant.

Show evidence (1 reference)

PMID:40429442 SUPPORT Human Clinical

"Among Japanese patients with VTE, the prevalence of protein S deficiency is 12.7%, while it is estimated from 0.48% to 0.63% in the general Japanese population"

Higher protein S deficiency prevalence in the Japanese population.

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Animal Models

3

Platelet-specific Pros1 knockout mouse (Pros1lox/loxPf4-Cre+)

A conditional knockout that eliminates protein S expression specifically in platelets (and their megakaryocyte precursors) while sparing the systemic, largely hepatocyte-derived plasma protein S pool.

Species

Mouse

Genotype

Pros1lox/loxPf4-Cre+ (platelet lineage-restricted Pros1 deletion via Platelet factor 4-Cre)

Publication

DOI:10.1182/blood.2019003630

Pathograph links

Reduced Protein S Cofactor Activity partially recapitulates fidelity: moderate Loss of platelet-derived protein S increases venous thrombus propensity by impairing its cofactor role for APC and TFPI, limiting factor X activation and thrombin generation within the growing thrombus at low shear rates. It does not increase arterial thrombosis propensity, unlike systemic human deficiency.

Limitations: This model isolates only the platelet-derived pool of protein S via a platelet-lineage-restricted knockout; it does not reproduce the systemic (predominantly hepatocyte-synthesized) protein S deficiency that defines the human hereditary disorder, so its venous-versus-arterial selectivity may not generalize to human global protein S deficiency.

Readouts

Venous (vena cava) thrombus propensity

Direction: INCREASED

Interpretation: Platelet protein S loss increases thrombus formation at low shear (vena cava) but not at high shear (carotid artery), consistent with a cofactor role for APC/TFPI-mediated factor X control within the growing venous thrombus.

Show evidence (1 reference)

DOI:10.1182/blood.2019003630 SUPPORT Model Organism

"inactivation of PSplt expression using the Platelet factor 4 (Pf4)-Cre transgene (Pros1lox/loxPf4-Cre+) in mice promotes thrombus propensity in the vena cava, where shear rates are low, but not in the carotid artery, where shear rates are high"

Directly reports the venous-specific thrombus-propensity phenotype of the platelet Pros1 knockout mouse.

Show evidence (1 reference)

DOI:10.1182/blood.2019003630 SUPPORT INDIRECT Model Organism

"At a low shear rate, PSplt functions as a cofactor for both activated protein C and tissue factor pathway inhibitor, thereby limiting factor X activation and thrombin generation within the growing thrombus"

Establishes the mechanistic role of protein S as an APC/TFPI cofactor limiting thrombin generation, informative for the reduced-cofactor node even though it isolates only the platelet-derived pool.

Global Pros1 knockout mouse (Pros1-/-)

Constitutive whole-body protein S null mouse - the closest model of the near-total protein S loss of the human biallelic (severe autosomal recessive) form.

Species

Mouse

Genotype

Pros1-/- (constitutive whole-body Pros1 deletion)

Publication

PMID:19729839

Pathograph links

Reduced Protein S Cofactor Activity partially recapitulates fidelity: moderate Complete protein S loss produces a fulminant coagulopathy with accelerated thrombin generation, including an activated-protein-C-independent component, modeling the anticoagulant-cofactor failure of severe deficiency.

Limitations: Pros1-/- mice die in utero from fulminant coagulopathy, whereas human biallelic neonates survive to present with purpura fulminans, so the model captures the coagulopathic severity but not the surviving neonatal course; it also shows vascular dysgenesis that is not part of the human hereditary thrombophilia phenotype.

Readouts

Plasma thrombin generation (aPC-independent component)

Direction: INCREASED

Interpretation: Accelerated thrombin generation in Pros1+/- plasma independent of aPC is in vivo evidence for an aPC-independent anticoagulant role of protein S, informative for the APC-versus-TFPI cofactor partition.

Show evidence (1 reference)

PMID:19729839 SUPPORT Model Organism

"plasma from Pros1+/- heterozygous mice exhibited accelerated thrombin generation independent of aPC"

Reports the aPC-independent accelerated thrombin generation readout of the protein S null model.

Show evidence (1 reference)

PMID:19729839 SUPPORT Model Organism

"all Pros1-/- mice die in utero,from a fulminant coagulopathy and associated hemorrhages"

Establishes the near-total protein S loss model as an informative, if embryonic-lethal, correlate of the severe biallelic human form.

Protein S K196E (Tokushima) knock-in mouse

Knock-in of the Japanese founder variant PROS1 p.Lys196Glu ("PS Tokushima") into the endogenous mouse Pros1 locus. Mice grow normally with normal protein S antigen but reduced APC-cofactor activity and exacerbated venous thrombosis.

Species

Mouse

Genotype

Pros1 p.Lys196Glu (K196E) knock-in

Publication

PMID:26251307

Pathograph links

Reduced Protein S Cofactor Activity recapitulates fidelity: moderate Reproduces a qualitative (Type II-like) defect: normal protein S antigen with selectively reduced APC-cofactor activity, and increased susceptibility to venous thrombosis.

Limitations: Mouse plasma has no detectable protein S TFPI-cofactor activity, so this model cannot test whether K196E dissociates the APC-cofactor from the TFPI-cofactor pathway; the model also does not aggravate ischemic stroke.

Readouts

Plasma APC-cofactor activity

Direction: DECREASED

Interpretation: The K196E mutant retains normal antigen but has selectively reduced APC anticoagulant cofactor activity - the molecular correlate of the reduced cofactor node.

Show evidence (1 reference)

PMID:26251307 SUPPORT Model Organism

"the purified PS-K196E mutant had 49% to 60% of normal PS APC cofactor activity."

Quantifies the selective reduction in APC-cofactor activity of the K196E protein.

Venous thrombosis susceptibility

Direction: INCREASED

Interpretation: K196E and heterozygous PS-deficient mice form larger venous thrombi and die more from induced pulmonary embolism than wild-type mice.

Show evidence (1 reference)

PMID:26251307 SUPPORT Model Organism

"Mice carrying a protein S-K196E mutation or heterozygous protein S deficiency were more vulnerable to venous thrombosis than wild-type mice."

Reports increased venous thrombosis susceptibility, grounding the exacerbated-VTE phenotype of this model.

Show evidence (1 reference)

PMID:26251307 SUPPORT Model Organism

"PS-K196E mice grew normally but had decreased activated protein C cofactor activity in plasma."

Establishes the K196E knock-in as an informative model of a qualitative reduced-APC-cofactor defect.

{ }

Source YAML

click to show

name: Protein S Deficiency
category: Mendelian
creation_date: "2026-09-03T00:00:00Z"
synonyms:
- hereditary protein S deficiency
- congenital protein S deficiency
- PROS1-related thrombophilia
- THPH5
- thrombophilia due to protein S deficiency, autosomal dominant
parents:
- Thrombophilia
description: >-
  A single-gene hereditary thrombophilia caused by loss-of-function variants in
  PROS1, the gene encoding protein S. Protein S is a vitamin K-dependent plasma
  glycoprotein that acts as a non-enzymatic cofactor for activated protein C
  (APC) in the proteolytic inactivation of coagulation factors Va and VIIIa, and,
  independently of APC, as a cofactor for tissue factor pathway inhibitor (TFPI).
  Roughly 60% of circulating protein S is bound to C4b-binding protein and is
  anticoagulantly inactive; only the free fraction (~40%) is functionally active.
  Reduced free/functional protein S weakens down-regulation of the coagulation
  cascade, favoring unopposed thrombin generation and predisposing to venous
  thromboembolism (deep vein thrombosis and pulmonary embolism). The common
  heterozygous form is autosomal dominant with incomplete penetrance; biallelic
  (homozygous or compound heterozygous) deficiency causes a severe neonatal
  presentation with purpura fulminans and massive venous thrombosis. Laboratory
  ISTH subtypes are Type I (quantitative), Type II (qualitative/dysfunctional),
  and Type III (selective free-protein-S deficiency).
notes: >-
  Scope: this entry covers PROS1-driven (hereditary) protein S deficiency
  specifically. It is a distinct single-gene Mendelian thrombophilia (THPH5,
  OMIM #612336; the severe autosomal recessive biallelic form is THPH6, OMIM
  #614514) and is deliberately kept separate from the general Thrombophilia
  umbrella entry (kb/disorders/Thrombophilia.yaml), which models the root
  hypercoagulable concept together with the five classic hereditary subtypes
  (factor V Leiden, prothrombin G20210A, and antithrombin, protein C, and
  protein S deficiencies). Acquired protein S deficiency (warfarin, vitamin K
  deficiency, liver disease, nephrotic syndrome, DIC, pregnancy, estrogen
  therapy, SLE, HIV) is mechanistically distinct and is noted here as a
  differential-diagnostic consideration rather than curated as PROS1 disease.
  Neonatal purpura fulminans in the severe biallelic form is managed acutely
  with fresh frozen plasma or protein S-containing plasma concentrate per
  clinical reviews (StatPearls, NORD; tertiary sources, not independently
  verified in this entry's evidence).

  MONDO scope: disease_term is MONDO:0012868 (the autosomal dominant form,
  THPH5). The entry also curates the severe biallelic form, so
  MONDO:0013791 (thrombophilia due to protein S deficiency, autosomal
  recessive; THPH6) is carried in mappings.mondo_mappings at
  skos:narrowMatch to retire that concept from the curation queue rather than
  leaving it unanchored. The broader parent concept MONDO:0019144 (hereditary
  thrombophilia due to congenital protein S deficiency) is deliberately NOT
  reused as disease_term here because it is already the subtype_term of the
  Protein S Deficiency subtype in kb/disorders/Thrombophilia.yaml; keeping the
  AD leaf as this entry's anchor and mapping the AR leaf avoids the two files
  silently claiming overlapping ontology scope.
disease_term:
  preferred_term: hereditary protein S deficiency
  term:
    id: MONDO:0012868
    label: thrombophilia due to protein S deficiency, autosomal dominant
mappings:
  mondo_mappings:
  - term:
      id: MONDO:0013791
      label: thrombophilia due to protein S deficiency, autosomal recessive
    mapping_predicate: skos:narrowMatch
    mapping_source: MONDO
    mapping_justification: >-
      The severe biallelic form (THPH6, OMIM #614514) is curated within this
      entry (AR inheritance block, Neonatal Purpura Fulminans, homozygous-patient
      evidence). Mapped at narrowMatch so the AR MONDO leaf is anchored and
      retired from the curation queue while the AD leaf remains the primary
      disease_term.
has_subtypes:
- name: Type I
  display_name: Type I (quantitative deficiency)
  description: >-
    Quantitative deficiency: reduced total protein S antigen, reduced free
    protein S antigen, and reduced protein S functional activity. One of the two
    most commonly encountered phenotypes clinically.
  genes:
  - preferred_term: PROS1
    term:
      id: hgnc:9456
      label: PROS1
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "type 1 (quantitative deficiency), characterized by low levels of total protein S (TPS) and free protein S (FPS), along with reduced protein S activity"
    explanation: ISTH classification defining Type I quantitative protein S deficiency.
- name: Type II
  display_name: Type II (qualitative/dysfunctional)
  description: >-
    Qualitative (functional) deficiency: normal total and free protein S
    antigen but decreased protein S functional activity, indicating a
    dysfunctional protein. The rarest of the three subtypes; the Japanese
    founder variant PROS1 p.Lys196Glu ("PS Tokushima") is a classic example.
  genes:
  - preferred_term: PROS1
    term:
      id: hgnc:9456
      label: PROS1
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "type 2 (functional deficiency, also known as type 2b), characterized by normal levels of TPS and FPS, but with decreased protein S activity, indicating a functional defect"
    explanation: ISTH classification defining Type II qualitative protein S deficiency.
- name: Type III
  display_name: Type III (selective free-protein-S deficiency)
  description: >-
    Selective free-protein-S deficiency: normal total protein S antigen but
    reduced free protein S antigen and reduced activity, reflecting an abnormal
    partitioning between the free and C4b-binding-protein-bound fractions. Along
    with Type I, one of the two most common phenotypes.
  genes:
  - preferred_term: PROS1
    term:
      id: hgnc:9456
      label: PROS1
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "type 3 (selective free protein s deficiency, also known as type 2a), characterized by normal TPS levels but reduced FPS and PS activity"
    explanation: ISTH classification defining Type III selective free-protein-S deficiency.
- name: Severe AR
  display_name: Severe Autosomal Recessive (Biallelic) Deficiency
  description: >-
    The severe biallelic (homozygous or compound heterozygous) form (THPH6,
    OMIM #614514, MONDO:0013791). In contrast to the common heterozygous
    autosomal dominant form, near-total loss of protein S activity presents in
    the neonatal period with purpura fulminans - disseminated microvascular
    thrombosis with hemorrhagic skin necrosis - and massive venous thrombosis.
    This clinical AD-mild / AR-severe axis is orthogonal to the ISTH laboratory
    Types I/II/III above.
  genes:
  - preferred_term: PROS1
    term:
      id: hgnc:9456
      label: PROS1
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a homozygous mutation presents with thrombotic events in early infancy and is often life-threatening"
    explanation: Defines the severe biallelic form as an early-infancy, life-threatening entity distinct from the mild heterozygous form.
pathophysiology:
- name: Reduced Protein S Cofactor Activity
  role: trigger
  biological_scale: MOLECULAR
  description: >-
    Loss-of-function PROS1 variants reduce the level or function of protein S, a
    hepatocyte-synthesized vitamin K-dependent glycoprotein that is a
    non-enzymatic cofactor for activated protein C (APC) in the inactivation of
    factors Va and VIIIa and, independently, for tissue factor pathway inhibitor
    (TFPI). Reduced free/functional protein S diminishes this anticoagulant
    cofactor activity.
  genes:
  - preferred_term: PROS1
    term:
      id: hgnc:9456
      label: PROS1
  genetic_context:
    gene:
      preferred_term: PROS1
      term:
        id: hgnc:9456
        label: PROS1
    variant_origin: GERMLINE
    functional_impact_category: LOSS_OF_FUNCTION
    description: >-
      Loss-of-function PROS1 variants. Zygosity is deliberately not recorded on
      this node because it is what separates the two clinical forms this entry
      models: heterozygous variants give the common, incompletely penetrant
      autosomal dominant deficiency, and biallelic variants give the severe
      neonatal recessive form (Severe AR subtype).
  cell_types:
  - preferred_term: hepatocyte
    term:
      id: CL:0000182
      label: hepatocyte
  biological_processes:
  - preferred_term: negative regulation of blood coagulation
    term:
      id: GO:0030195
      label: negative regulation of blood coagulation
    modifier: DECREASED
  molecular_functions:
  - preferred_term: APC anticoagulant cofactor (enzyme activator) activity
    term:
      id: GO:0008047
      label: enzyme activator activity
    modifier: DECREASED
  evidence:
  - reference: PMID:42429079
    reference_title: "Protein S: a vitamin K-dependent factor bridging haemostasis, tissue homeostasis and cancer."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Protein S (PROS1) is a vitamin K-dependent plasma glycoprotein that was originally described as a non-enzymatic cofactor of activated protein C in the regulation of blood coagulation."
    explanation: Establishes the causal gene and the classic non-enzymatic APC-cofactor role of protein S.
  - reference: PMID:41180656
    reference_title: "Warfarin-induced skin necrosis: a narrative review of clinical features, risk factors, and treatment strategies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Protein S enhances the anticoagulant effect of protein C by serving as its cofactor; thus, deficiency in either protein leads to impaired inactivation of factors Va and VIIIa, fostering a prothrombotic state"
    explanation: Directly describes the cofactor mechanism and the prothrombotic consequence of its loss.
  - reference: DOI:10.1182/blood.2019003630
    reference_title: Platelet protein S limits venous but not arterial thrombosis propensity by controlling coagulation in the thrombus
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "At a low shear rate, PSplt functions as a cofactor for both activated protein C and tissue factor pathway inhibitor, thereby limiting factor X activation and thrombin generation within the growing thrombus"
    explanation: Mouse-model evidence for the dual APC/TFPI cofactor mechanism of protein S in limiting thrombin generation.
  downstream:
  - target: Unopposed Thrombin Generation and Fibrin Formation
    causal_link_type: DIRECT
    description: >-
      Diminished APC/TFPI cofactor activity allows sustained factor Va/VIIIa and
      factor Xa activity, amplifying thrombin generation.
  - target: Reduced Protein S Activity
    causal_link_type: DIRECT
    description: >-
      Reduced protein S cofactor function is measured directly as reduced protein
      S functional (APC-cofactor) activity - the diagnostic laboratory readout of
      this molecular defect.
    evidence:
    - reference: PMID:40429442
      reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "PS functional activity assays measure the biological activity of PS by assessing its ability to function as a cofactor for APC in the inactivation of FVa and FVIIIa."
      explanation: The functional activity assay reads out the reduced APC-cofactor activity of this molecular node.
  - target: Warfarin-Induced Transient Anticoagulant Depletion
    causal_link_type: DIRECT
    description: >-
      A deficient protein S baseline makes the transient post-warfarin fall in
      protein S (and protein C) activity proportionally more severe on
      initiation of a vitamin K antagonist.
- name: Unopposed Thrombin Generation and Fibrin Formation
  role: central_effector
  biological_scale: CELLULAR
  conforms_to: "thrombogenesis#Coagulation Cascade Activation and Thrombin-Driven Fibrin Formation"
  description: >-
    With natural anticoagulant down-regulation weakened, the coagulation cascade
    proceeds toward unchecked thrombin generation and thrombin-driven conversion
    of fibrinogen into an insoluble fibrin network.
  cell_types:
  - preferred_term: platelet
    term:
      id: CL:0000233
      label: platelet
  biological_processes:
  - preferred_term: blood coagulation
    term:
      id: GO:0007596
      label: blood coagulation
    modifier: INCREASED
  - preferred_term: fibrin clot formation
    term:
      id: GO:0072378
      label: blood coagulation, fibrin clot formation
    modifier: INCREASED
  evidence:
  - reference: PMID:41180656
    reference_title: "Warfarin-induced skin necrosis: a narrative review of clinical features, risk factors, and treatment strategies."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Protein C and protein S are vitamin K-dependent glycoproteins that function as critical anticoagulants by regulating the coagulation cascade."
    explanation: Establishes protein S as a critical anticoagulant regulator whose loss releases coagulation-cascade activity.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The coagulation cascade, composed of intrinsic and extrinsic pathways, culminates in the activation of thrombin, which converts fibrinogen to fibrin"
    explanation: Describes the thrombin-driven fibrin-formation step that this node represents.
  downstream:
  - target: Venous Thrombus Formation
    causal_link_type: DIRECT
    description: >-
      Excess thrombin and fibrin, particularly under the low-shear conditions of
      venous flow, drive pathological venous thrombus formation.
  - target: Disseminated Microvascular Thrombosis
    causal_link_type: DIRECT
    description: >-
      In severe biallelic deficiency the near-total loss of anticoagulant control
      drives widespread small-vessel (microvascular) fibrin thrombosis, distinct
      from the large-vein thrombus of the common heterozygous form.
    evidence:
    - reference: PMID:24144709
      reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "She developed purpura fulminans at birth and a catheter-related venous thrombosis complicated by massive pulmonary embolism at the sixth day of life."
      explanation: Documents the disseminated microvascular thrombosis (purpura fulminans) of severe biallelic deficiency, a distinct downstream branch from large-vein thrombus.
- name: Venous Thrombus Formation
  role: central_effector
  biological_scale: TISSUE
  conforms_to: "thrombogenesis#Pathological Fibrin-Platelet Thrombus Formation"
  description: >-
    Formation of a pathological intravascular fibrin-platelet thrombus, most
    often in the deep veins of the lower extremities, which may propagate or
    embolize to the pulmonary arteries.
  cell_types:
  - preferred_term: platelet
    term:
      id: CL:0000233
      label: platelet
  biological_processes:
  - preferred_term: blood coagulation, fibrin clot formation
    term:
      id: GO:0072378
      label: blood coagulation, fibrin clot formation
    modifier: INCREASED
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "A deficiency in PS disrupts normal coagulation control, leading to an increased risk of thrombophilia and VTE due to an excessive blood clot formation"
    explanation: Directly links reduced protein S to excessive clot formation and venous thromboembolism.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Fibrin serves as the structural framework of the thrombus, stabilizing platelet aggregates and incorporating red blood cells."
    explanation: Describes the fibrin-platelet composition of the thrombus this node represents.
  downstream:
  - target: Deep venous thrombosis
    causal_link_type: DIRECT
    description: A lower-extremity deep venous thrombus is the most common clinical manifestation.
  - target: Pulmonary embolism
    causal_link_type: DIRECT
    description: A venous thrombus may dislodge and embolize to the pulmonary arteries.
  - target: Superficial thrombophlebitis
    causal_link_type: DIRECT
    description: >-
      Superficial-vein thrombosis (thrombophlebitis) is a frequent parallel
      venous manifestation of the same hypercoagulable state, second in frequency
      only to deep venous thrombosis among symptomatic carriers.
    evidence:
    - reference: PMID:2952034
      reference_title: "Hereditary protein S deficiency: clinical manifestations."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "Most symptomatic patients had various combinations of deep venous thrombosis (74%), superficial thrombophlebitis (72%), and pulmonary embolism (38%)"
      explanation: Documents superficial thrombophlebitis as a high-frequency venous manifestation in hereditary protein S deficiency.
- name: Disseminated Microvascular Thrombosis
  role: central_effector
  biological_scale: TISSUE
  description: >-
    Widespread small-vessel (microvascular) fibrin thrombosis of the skin and
    other tissues in severe biallelic protein S deficiency, the lesion
    underlying neonatal purpura fulminans. Distinct from the large-vein
    fibrin-platelet thrombus of the common heterozygous form.
  cell_types:
  - preferred_term: platelet
    term:
      id: CL:0000233
      label: platelet
  biological_processes:
  - preferred_term: blood coagulation, fibrin clot formation
    term:
      id: GO:0072378
      label: blood coagulation, fibrin clot formation
    modifier: INCREASED
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a homozygous mutation presents with thrombotic events in early infancy and is often life-threatening"
    explanation: Establishes the severe, early-onset thrombotic process of biallelic deficiency that manifests as microvascular purpura fulminans.
  downstream:
  - target: Neonatal Purpura Fulminans
    causal_link_type: DIRECT
    description: >-
      Disseminated microvascular thrombosis produces the hemorrhagic skin
      necrosis of neonatal purpura fulminans.
    evidence:
    - reference: PMID:24144709
      reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "We report a case of a 6-year-old girl with severe protein S deficiency due to a homozygous mutation and recurrent episodes of skin necrosis. She developed purpura fulminans at birth"
      explanation: Links the microvascular thrombotic process of severe deficiency to the purpura fulminans / skin necrosis phenotype.
- name: Warfarin-Induced Transient Anticoagulant Depletion
  role: modifier
  biological_scale: MOLECULAR
  description: >-
    Because protein S (and protein C) have short plasma half-lives relative to
    the procoagulant vitamin K-dependent factors, initiating a vitamin K
    antagonist transiently deepens the anticoagulant deficit before procoagulant
    factors fall, producing a brief hypercoagulable window that can precipitate
    microvascular skin necrosis in an already-deficient patient.
  biological_processes:
  - preferred_term: negative regulation of blood coagulation
    term:
      id: GO:0030195
      label: negative regulation of blood coagulation
    modifier: DECREASED
  evidence:
  - reference: PMID:9885367
    reference_title: "Recurrent warfarin-induced skin necrosis in kindreds with protein S deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Coumarin skin necrosis occurs almost exclusively in patients with venous thrombosis between the 3rd and 10th day after beginning anticoagulation."
    explanation: Establishes the early-initiation timing window of the warfarin-induced hypercoagulable state.
  - reference: PMID:24144709
    reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Vitamin K antagonists decrease plasma level of vitamin K-dependent coagulation proteins, including the natural anticoagulant protein C."
    explanation: Documents the vitamin K antagonist-driven fall in natural anticoagulants underlying this node.
  downstream:
  - target: Warfarin-Induced Skin Necrosis
    causal_link_type: DIRECT
    description: >-
      The transient hypercoagulable window drives microvascular thrombosis of
      the skin and subcutaneous fat.
phenotypes:
- name: Deep venous thrombosis
  category: Physical
  phenotype_term:
    preferred_term: Deep venous thrombosis
    term:
      id: HP:0002625
      label: Deep venous thrombosis
  frequency: Most common manifestation; ~74% of symptomatic carriers in the classic family series.
  description: >-
    Deep vein thrombosis, typically of the lower extremities, is the most common
    clinical manifestation of hereditary protein S deficiency. (About half of
    heterozygous carriers develop venous thromboembolism overall over their
    lifetime - a composite VTE endpoint stated at the disease level in the
    inheritance block.)
  evidence:
  - reference: PMID:2952034
    reference_title: "Hereditary protein S deficiency: clinical manifestations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most symptomatic patients had various combinations of deep venous thrombosis (74%), superficial thrombophlebitis (72%), and pulmonary embolism (38%)"
    explanation: Quantifies deep venous thrombosis as the most frequent manifestation among symptomatic carriers.
- name: Superficial thrombophlebitis
  category: Physical
  phenotype_term:
    preferred_term: Superficial thrombophlebitis
    term:
      id: HP:0002638
      label: Superficial thrombophlebitis
  frequency: ~72% of symptomatic carriers in the classic family series; second only to deep venous thrombosis.
  description: >-
    Superficial-vein thrombophlebitis is a frequent venous manifestation of
    hereditary protein S deficiency, second in frequency only to deep venous
    thrombosis among symptomatic carriers.
  evidence:
  - reference: PMID:2952034
    reference_title: "Hereditary protein S deficiency: clinical manifestations."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Most symptomatic patients had various combinations of deep venous thrombosis (74%), superficial thrombophlebitis (72%), and pulmonary embolism (38%)"
    explanation: Quantifies superficial thrombophlebitis frequency among symptomatic protein S-deficient patients.
- name: Pulmonary embolism
  category: Physical
  phenotype_term:
    preferred_term: Pulmonary embolism
    term:
      id: HP:0002204
      label: Pulmonary embolism
  description: >-
    Pulmonary embolism results from embolization of a venous thrombus and can be
    life-threatening, including in the severe neonatal form.
  evidence:
  - reference: PMID:24144709
    reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "She developed purpura fulminans at birth and a catheter-related venous thrombosis complicated by massive pulmonary embolism at the sixth day of life."
    explanation: Documents massive pulmonary embolism in a patient with severe (homozygous) protein S deficiency.
- name: Neonatal Purpura Fulminans
  category: Physical
  subtype: Severe AR
  phenotype_term:
    preferred_term: Neonatal purpura fulminans
    term:
      id: HP:0000979
      label: Purpura
  description: >-
    Severe biallelic (homozygous or compound heterozygous) protein S deficiency
    presents in the neonatal period with purpura fulminans - widespread
    microvascular thrombosis producing hemorrhagic skin necrosis - and massive
    venous thrombosis, a life-threatening emergency.
  notes: >-
    HPO has no dedicated "purpura fulminans" term; HP:0000979 Purpura is the
    closest bindable phenotype. The neonatal onset and severity are the cited
    claim here.
  evidence:
  - reference: PMID:24144709
    reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "We report a case of a 6-year-old girl with severe protein S deficiency due to a homozygous mutation and recurrent episodes of skin necrosis. She developed purpura fulminans at birth"
    explanation: Directly reports neonatal purpura fulminans in homozygous (severe) protein S deficiency.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "a homozygous mutation presents with thrombotic events in early infancy and is often life-threatening"
    explanation: Establishes the early-infancy, life-threatening presentation of biallelic protein S deficiency.
- name: Reduced Protein S Activity
  category: Laboratory
  phenotype_term:
    preferred_term: Reduced protein S activity
    term:
      id: HP:0004855
      label: Reduced protein S activity
  description: The diagnostic laboratory hallmark of protein S deficiency.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PS functional activity assays measure the biological activity of PS by assessing its ability to function as a cofactor for APC in the inactivation of FVa and FVIIIa."
    explanation: Establishes reduced protein S functional (APC-cofactor) activity as the laboratory phenotype.
- name: Warfarin-Induced Skin Necrosis
  category: Physical
  phenotype_term:
    preferred_term: Warfarin-induced skin necrosis
    term:
      id: HP:0001038
      label: Warfarin-induced skin necrosis
  description: >-
    An uncommon but serious complication of vitamin K antagonist initiation,
    classically linked to protein C deficiency and rarely to congenital protein
    S deficiency.
  evidence:
  - reference: PMID:9885367
    reference_title: "Recurrent warfarin-induced skin necrosis in kindreds with protein S deficiency."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Although protein C deficiency is the most common underlying hypercoagulable state reportedly associated with warfarin skin necrosis, very few cases have been linked to congenital protein S deficiency."
    explanation: Establishes warfarin-induced skin necrosis as a recognized complication of congenital protein S deficiency.
genetic:
- name: PROS1
  gene_term:
    preferred_term: PROS1
    term:
      id: hgnc:9456
      label: PROS1
  relationship_type: CAUSATIVE
  association: >-
    Loss-of-function PROS1 variants cause hereditary protein S deficiency.
    Heterozygous variants cause the common, incompletely penetrant autosomal
    dominant form (THPH5); biallelic variants cause the severe autosomal
    recessive neonatal form (THPH6). More than 200 distinct PROS1 variants
    have been reported, predominantly point mutations, including transversions
    producing a premature stop codon and a truncated, nonfunctional protein.
  inheritance:
  - name: Autosomal dominant inheritance
    inheritance_term:
      preferred_term: Autosomal dominant inheritance
      term:
        id: HP:0000006
        label: Autosomal dominant inheritance
    penetrance: INCOMPLETE
    description: >-
      Heterozygous PROS1 variants cause the common, incompletely penetrant mild
      deficiency.
  - name: Autosomal recessive inheritance
    inheritance_term:
      preferred_term: Autosomal recessive inheritance
      term:
        id: HP:0000007
        label: Autosomal recessive inheritance
    description: >-
      Homozygous or compound heterozygous PROS1 variants cause a severe,
      life-threatening deficiency presenting as neonatal purpura fulminans.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Mutations in the PROS1 gene are responsible for congenital PS deficiency"
    explanation: Establishes PROS1 as the causal gene for congenital protein S deficiency.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Over 200 different PROS1 mutations have been identified, giving rise to distinct forms of PS deficiency."
    explanation: Documents the allelic heterogeneity of PROS1 variants.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Heterozygous mutation typically exhibit a mild PS deficiency, whereas homozygous or compound heterozygous mutations result in severe PS deficiency, which can lead to life-threatening thrombotic complications."
    explanation: Establishes the dominant-mild versus biallelic-severe genotype-phenotype relationship.
- name: F5
  gene_term:
    preferred_term: F5
    term:
      id: hgnc:3542
      label: F5
  relationship_type: MODIFIER
  association: >-
    Co-inheritance of the factor V Leiden variant (F5 c.1601G>A, p.Arg534Gln;
    legacy R506Q) is a common second thrombophilic hit in PROS1-deficient
    families and sharply raises thrombotic risk and lowers age at first event.
    Factor V Leiden was present in 29-38% of symptomatic protein S-deficient
    probands across two family studies; in sibships co-segregating both defects,
    80% of double-carriers were symptomatic; and mean age at first thrombosis was
    18.4 years in combined-defect carriers versus 32.6 years with a single defect.
  notes: >-
    The co-inheritance effect-size magnitudes (co-segregation rate, age at first
    event) are carried in the association text and the evidence snippets rather
    than a structured numeric field, because the Genetic class has no dedicated
    per-modifier odds-ratio / effect-size slot.
  evidence:
  - reference: PMID:8584987
    reference_title: "Factor V Leiden: an additional risk factor for thrombosis in protein S deficient families?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In sibships where both abnormalities were segregating, the percentage of symptomatic individuals with both abnormalities was 80%."
    explanation: Quantifies the fraction of symptomatic double-carriers when factor V Leiden co-segregates with protein S deficiency.
  - reference: PMID:8584987
    reference_title: "Factor V Leiden: an additional risk factor for thrombosis in protein S deficient families?"
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among 16 symptomatic protein S deficient probands the prevalence of the FV Leiden mutation was high (38%)."
    explanation: Documents the high factor V Leiden prevalence among symptomatic protein S-deficient probands (selection reflects familial thrombosis referral).
  - reference: PMID:9607123
    reference_title: "Clinical features of thrombophilia in families with gene defects in protein C or protein S combined with factor V Leiden."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The age at first thrombosis was significantly lower (P < 0.001) in the ten propositi with a combined genetic defect (mean age 18.4 +/- 6.6 years) than in those with a single defect (mean age 32.6 +/- 10.4 years)."
    explanation: Quantifies the earlier age at first thrombosis when a second defect (factor V Leiden) is co-inherited with protein C/S deficiency.
inheritance:
- name: Autosomal dominant inheritance
  inheritance_term:
    preferred_term: Autosomal dominant inheritance
    term:
      id: HP:0000006
      label: Autosomal dominant inheritance
  penetrance: INCOMPLETE
  description: >-
    The common hereditary protein S deficiency (THPH5) is autosomal dominant
    with incomplete penetrance; about half of heterozygous carriers remain
    asymptomatic.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Congenital PS deficiency follows an autosomal dominant inheritance pattern."
    explanation: States the autosomal dominant inheritance pattern of congenital protein S deficiency.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Approximately 50% of heterozygous individuals develop VTE, while the remaining half remain asymptomatic throughout their lives."
    explanation: Documents the incomplete penetrance of the heterozygous form.
prevalence:
- population: General population (mild congenital deficiency)
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_per_100000: 200.0
  notes: >-
    Source phrasing "the estimated incidence of mild congenital PS deficiency is
    approximately 1 in 500 individuals"; 1 in 500 = 200 per 100,000.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The estimated incidence of mild congenital PS deficiency is approximately 1 in 500 individuals, while severe PS deficiency is exceedingly rare, with an unknown prevalence due to diagnostic challenges"
    explanation: Population estimate for mild congenital protein S deficiency; severe biallelic form is exceedingly rare.
- population: Healthy blood donors (familial protein S deficiency)
  measure_type: POINT_PREVALENCE
  prevalence_class: BAND_1_5_PER_10000
  rate_low: 30.0
  rate_high: 130.0
  notes: >-
    Source phrasing "the prevalence of familial PS deficiency ranged between
    0.03% and 0.13%" among healthy blood donors (30-130 per 100,000). Rises to
    3-5% among patients selected for recurrent thrombosis or family history.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "In a study of healthy blood donors, the prevalence of familial PS deficiency ranged between 0.03% and 0.13%. However, the prevalence increases significantly among patients with recurrent thrombosis or a family history of thrombosis, ranging from 3% to 5%"
    explanation: Blood-donor screening prevalence and its increase in thrombosis-referral cohorts.
- population: General Japanese population
  measure_type: POINT_PREVALENCE
  prevalence_class: ABOVE_1_IN_1000
  rate_low: 480.0
  rate_high: 630.0
  notes: >-
    Source phrasing "estimated from 0.48% to 0.63% in the general Japanese
    population" (480-630 per 100,000); higher than in the US/Europe, partly due
    to the Japan-specific PROS1 p.Lys196Glu ("PS Tokushima") founder variant.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Among Japanese patients with VTE, the prevalence of protein S deficiency is 12.7%, while it is estimated from 0.48% to 0.63% in the general Japanese population"
    explanation: Higher protein S deficiency prevalence in the Japanese population.
biochemical:
- name: Free Protein S Antigen
  biomarker_term:
    preferred_term: Free Protein S Measurement
    term:
      id: NCIT:C122142
      label: Free Protein S Measurement
  presence: Decreased
  context: >-
    Free protein S antigen measures the functionally active, non-C4BP-bound
    fraction (~40% of total) and is the most reliable screening measurement: it
    is reduced in Types I and III. Interpretation is sex- and age-stratified
    (women have lower free and total protein S than men) and results are repeated
    in stable conditions off pregnancy, hormonal therapy, acute thrombosis, and
    anticoagulation.
  readouts:
  - target: Reduced Protein S Cofactor Activity
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      Lower free protein S antigen tracks with lower anticoagulant cofactor
      activity; the free fraction is the functionally active pool.
    evidence:
    - reference: PMID:40429442
      reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "The free form is functionally active."
      explanation: Establishes free protein S antigen as the functionally active fraction that reports on cofactor activity.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, women generally have lower total and free protein S levels than men. Total PS levels increase with age, particularly in women, due to hormonal variations, whereas free PS levels remain stable over time."
    explanation: Establishes the sex- and age-dependence of protein S antigen levels, which stratifies reference-range interpretation.
- name: Total Protein S Antigen
  biomarker_term:
    preferred_term: Protein S Measurement
    term:
      id: NCIT:C100436
      label: Protein S Measurement
  presence: Decreased or normal
  context: >-
    Total protein S antigen (free plus C4BP-bound) is reduced in Type I
    (quantitative) deficiency but normal in Types II and III, so it detects Type
    I but misses the qualitative and selective-free subtypes.
  readouts:
  - target: Reduced Protein S Cofactor Activity
    relationship: READOUT_OF
    direction: NEGATIVE
    endpoint_context: DIAGNOSTIC
    interpretation: >-
      A low total protein S antigen indicates quantitative (Type I) deficiency;
      a normal total with reduced activity indicates Type II/III.
    evidence:
    - reference: PMID:40429442
      reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "type 1 (quantitative deficiency), characterized by low levels of total protein S (TPS) and free protein S (FPS), along with reduced protein S activity"
      explanation: Total protein S antigen is reduced in Type I deficiency, the readout distinguishing quantitative from qualitative subtypes.
diagnosis:
- name: "Protein S Deficiency: Free Antigen and Functional Activity Assay"
  description: >-
    Protein S functional activity is assessed by its ability to act as an APC
    cofactor in inactivating factors Va and VIIIa; free and total protein S
    antigen are measured separately by immunoassay. Free protein S antigen is
    the most reliable screen because it reflects the functionally active,
    non-C4BP-bound fraction; total antigen detects Type I but not Type II or III.
    Reference ranges are sex-, age-, and pregnancy-dependent (women have lower
    total and free protein S than men; total protein S rises with age), so
    results must be interpreted against stratified ranges and repeated outside
    pregnancy, hormonal therapy, acute thrombosis, and anticoagulation. Factor V
    Leiden can cause falsely low functional protein S in older clot-based assays.
  diagnosis_term:
    preferred_term: coagulation study
    term:
      id: NCIT:C62662
      label: Coagulation Study
  results: Reduced free and/or total protein S antigen, or reduced protein S functional activity with normal antigen (Type II/III).
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "PS functional activity assays measure the biological activity of PS by assessing its ability to function as a cofactor for APC in the inactivation of FVa and FVIIIa."
    explanation: Directly describes the functional-cofactor basis of the protein S activity assay.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Notably, women generally have lower total and free protein S levels than men. Total PS levels increase with age, particularly in women, due to hormonal variations, whereas free PS levels remain stable over time."
    explanation: Establishes the sex- and age-dependence of protein S reference ranges.
- name: "PROS1 Molecular Genetic Testing"
  description: >-
    After a functional/antigen abnormality is confirmed and acquired causes are
    excluded, PROS1 sequencing confirms hereditary deficiency; the ISTH maintains
    a registry of documented PROS1 mutations. Because many acquired and
    physiologic states lower protein S, laboratory testing must be repeated in
    stable conditions before a hereditary diagnosis is made. (Note: the exact
    ISTH-SSC criterion of two abnormal results >=4 weeks apart, and large-deletion
    detection by MLPA, are standard practice but are not stated in this entry's
    cited review and are therefore not asserted here with a snippet.)
  diagnosis_term:
    preferred_term: PROS1 genetic testing
    term:
      id: NCIT:C15709
      label: Genetic Testing
  results: A pathogenic or likely-pathogenic PROS1 variant confirms hereditary protein S deficiency.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "After ruling out acquired causes and if a hereditary deficiency is suspected, PROS1 genetic testing should be performed."
    explanation: Establishes PROS1 sequencing as the confirmatory molecular test after acquired causes are excluded.
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Thus, repeat testing in stable conditions is recommended."
    explanation: Establishes the requirement to repeat testing in stable conditions before a hereditary diagnosis.
treatments:
- name: Long-Term Anticoagulation with Heparin-Bridged Initiation
  description: >-
    Anticoagulation (a vitamin K antagonist such as warfarin, or a direct oral
    anticoagulant such as rivaroxaban) reduces the risk of recurrent venous
    thromboembolism; duration is individualized to recurrence versus bleeding
    risk. When warfarin is used, initiation should be bridged with heparin and
    avoid high loading doses, because unbridged warfarin can precipitate
    warfarin-induced skin necrosis in protein S (or protein C) deficiency. Direct
    oral anticoagulants avoid this mechanism and are an alternative, including in
    severe deficiency with recurrent warfarin necrosis.
  treatment_term:
    preferred_term: anticoagulation therapy
    term:
      id: NCIT:C63341
      label: Anticoagulation Therapy
    therapeutic_agent:
    - preferred_term: warfarin
      term:
        id: CHEBI:10033
        label: warfarin
    - preferred_term: rivaroxaban
      term:
        id: CHEBI:68579
        label: rivaroxaban
  therapeutic_modality: SMALL_MOLECULE
  target_mechanisms:
  - target: Unopposed Thrombin Generation and Fibrin Formation
    treatment_effect: INHIBITS
    description: >-
      Vitamin K antagonism or direct factor Xa inhibition suppresses ongoing
      coagulation-cascade activation, reducing the risk of recurrent thrombosis.
  - target: Warfarin-Induced Transient Anticoagulant Depletion
    treatment_effect: BYPASSES
    description: >-
      Heparin bridging during warfarin initiation, or use of a direct oral
      anticoagulant instead of warfarin, avoids the transient protein C/S
      depletion window that can precipitate skin necrosis.
  evidence:
  - reference: PMID:24144709
    reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "The switch of anticoagulant therapy from warfarin to rivaroxaban, a direct inhibitor of activated factor X that does not inhibit other vitamin K-dependent proteins, resulted in the disappearance of skin necrosis at 1 year of follow-up."
    explanation: Documents a direct oral anticoagulant as an effective alternative avoiding warfarin-induced skin necrosis in severe protein S deficiency.
  - reference: PMID:24144709
    reference_title: Anticoagulant treatment with rivaroxaban in severe protein S deficiency.
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "Rivaroxaban may be considered as a valid anticoagulant alternative in patients with severe inherited protein S deficiency and warfarin-induced skin necrosis."
    explanation: States the therapeutic recommendation for a direct oral anticoagulant in this setting.
- name: Pregnancy Thromboprophylaxis with Low-Molecular-Weight Heparin
  description: >-
    Pregnancy is the single highest-risk window in hereditary thrombophilia.
    Low-molecular-weight heparin is the preferred antepartum and postpartum
    thromboprophylaxis because it does not cross the placenta; obstetric risk
    schemes (e.g., RCOG) that incorporate inherited thrombophilia guide when it
    is indicated. Vitamin K antagonists are generally avoided in pregnancy (and
    carry the additional protein S-specific skin-necrosis risk noted above).
  treatment_term:
    preferred_term: Anticoagulation Therapy
    term:
      id: NCIT:C63341
      label: Anticoagulation Therapy
    therapeutic_agent:
    - preferred_term: low-molecular-weight heparin
      term:
        id: NCIT:C2578
        label: Low Molecular Weight Heparin
  target_mechanisms:
  - target: Venous Thrombus Formation
    treatment_effect: INHIBITS
    description: >-
      LMWH prophylaxis suppresses thrombin generation and venous thrombus
      formation during the high-risk peripartum period.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "potentially indicating the need for low-molecular-weight heparin prophylaxis"
    explanation: Obstetric risk schemes incorporating inherited thrombophilia indicate LMWH prophylaxis in pregnancy.
environmental:
- name: Estrogen-Containing Oral Contraceptive or Hormone Therapy
  exposure_term:
    preferred_term: exposure to oral contraceptive
    term:
      id: ECTO:9002149
      label: exposure to oral contraceptive
  description: >-
    Exogenous estrogen physiologically lowers free protein S and supplies a
    "second hit" that can precipitate venous thromboembolism in a carrier of an
    otherwise silent hereditary protein S deficiency genotype.
  evidence:
  - reference: PMID:40429442
    reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
    supports: SUPPORT
    evidence_source: HUMAN_CLINICAL
    snippet: "vitamin K deficiency, liver disease, DIC, nephrotic syndrome due to protein S loss, pregnancy, oral contraceptives, hormone replacement therapy"
    explanation: Lists oral contraceptives and hormone replacement therapy among the acquired states that lower protein S levels.
  influences_mechanisms:
  - target: Venous Thrombus Formation
    environmental_effect: EXACERBATES
    causal_link_type: DIRECT
    description: >-
      Estrogen exposure amplifies venous thrombosis risk on a background of
      reduced protein S.
    evidence:
    - reference: PMID:40429442
      reference_title: "From Circulating Biomarkers to Polymorphic Variants: A Narrative Review of Challenges in Thrombophilia Evaluation."
      supports: SUPPORT
      evidence_source: HUMAN_CLINICAL
      snippet: "vitamin K deficiency, liver disease, warfarin therapy, pregnancy and hormonal therapy, nephrotic syndrome, severe infections or inflammatory states (downregulation of protein S synthesis), and FV Leiden causes false low PS levels"
      explanation: Documents pregnancy and hormonal therapy as states that lower protein S levels, amplifying thrombotic risk.
animal_models:
- name: Platelet-specific Pros1 knockout mouse (Pros1lox/loxPf4-Cre+)
  species: Mouse
  genotype: Pros1lox/loxPf4-Cre+ (platelet lineage-restricted Pros1 deletion via Platelet factor 4-Cre)
  publication: DOI:10.1182/blood.2019003630
  description: >-
    A conditional knockout that eliminates protein S expression specifically in
    platelets (and their megakaryocyte precursors) while sparing the systemic,
    largely hepatocyte-derived plasma protein S pool.
  modeled_mechanisms:
  - target: Reduced Protein S Cofactor Activity
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Loss of platelet-derived protein S increases venous thrombus propensity by
      impairing its cofactor role for APC and TFPI, limiting factor X activation
      and thrombin generation within the growing thrombus at low shear rates. It
      does not increase arterial thrombosis propensity, unlike systemic human
      deficiency.
    limitations: >-
      This model isolates only the platelet-derived pool of protein S via a
      platelet-lineage-restricted knockout; it does not reproduce the systemic
      (predominantly hepatocyte-synthesized) protein S deficiency that defines
      the human hereditary disorder, so its venous-versus-arterial selectivity
      may not generalize to human global protein S deficiency.
    readouts:
    - name: Venous (vena cava) thrombus propensity
      target: Reduced Protein S Cofactor Activity
      direction: INCREASED
      interpretation: >-
        Platelet protein S loss increases thrombus formation at low shear (vena
        cava) but not at high shear (carotid artery), consistent with a cofactor
        role for APC/TFPI-mediated factor X control within the growing venous
        thrombus.
      evidence:
      - reference: DOI:10.1182/blood.2019003630
        reference_title: "Platelet protein S limits venous but not arterial thrombosis propensity by controlling coagulation in the thrombus"
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "inactivation of PSplt expression using the Platelet factor 4 (Pf4)-Cre transgene (Pros1lox/loxPf4-Cre+) in mice promotes thrombus propensity in the vena cava, where shear rates are low, but not in the carotid artery, where shear rates are high"
        explanation: Directly reports the venous-specific thrombus-propensity phenotype of the platelet Pros1 knockout mouse.
  evidence:
  - reference: DOI:10.1182/blood.2019003630
    reference_title: "Platelet protein S limits venous but not arterial thrombosis propensity by controlling coagulation in the thrombus"
    supports: SUPPORT
    directness: INDIRECT
    evidence_source: MODEL_ORGANISM
    snippet: "At a low shear rate, PSplt functions as a cofactor for both activated protein C and tissue factor pathway inhibitor, thereby limiting factor X activation and thrombin generation within the growing thrombus"
    explanation: >-
      Establishes the mechanistic role of protein S as an APC/TFPI cofactor
      limiting thrombin generation, informative for the reduced-cofactor node
      even though it isolates only the platelet-derived pool.
- name: Global Pros1 knockout mouse (Pros1-/-)
  species: Mouse
  genotype: Pros1-/- (constitutive whole-body Pros1 deletion)
  publication: PMID:19729839
  description: >-
    Constitutive whole-body protein S null mouse - the closest model of the
    near-total protein S loss of the human biallelic (severe autosomal recessive)
    form.
  modeled_mechanisms:
  - target: Reduced Protein S Cofactor Activity
    relationship: PARTIALLY_RECAPITULATES
    fidelity: MODERATE
    description: >-
      Complete protein S loss produces a fulminant coagulopathy with accelerated
      thrombin generation, including an activated-protein-C-independent component,
      modeling the anticoagulant-cofactor failure of severe deficiency.
    limitations: >-
      Pros1-/- mice die in utero from fulminant coagulopathy, whereas human
      biallelic neonates survive to present with purpura fulminans, so the model
      captures the coagulopathic severity but not the surviving neonatal course;
      it also shows vascular dysgenesis that is not part of the human hereditary
      thrombophilia phenotype.
    readouts:
    - name: Plasma thrombin generation (aPC-independent component)
      target: Reduced Protein S Cofactor Activity
      direction: INCREASED
      interpretation: >-
        Accelerated thrombin generation in Pros1+/- plasma independent of aPC is
        in vivo evidence for an aPC-independent anticoagulant role of protein S,
        informative for the APC-versus-TFPI cofactor partition.
      evidence:
      - reference: PMID:19729839
        reference_title: Lack of protein S in mice causes embryonic lethal coagulopathy and vascular dysgenesis.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "plasma from Pros1+/- heterozygous mice exhibited accelerated thrombin generation independent of aPC"
        explanation: Reports the aPC-independent accelerated thrombin generation readout of the protein S null model.
  evidence:
  - reference: PMID:19729839
    reference_title: Lack of protein S in mice causes embryonic lethal coagulopathy and vascular dysgenesis.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "all Pros1-/- mice die in utero,from a fulminant coagulopathy and associated hemorrhages"
    explanation: Establishes the near-total protein S loss model as an informative, if embryonic-lethal, correlate of the severe biallelic human form.
- name: Protein S K196E (Tokushima) knock-in mouse
  species: Mouse
  genotype: Pros1 p.Lys196Glu (K196E) knock-in
  publication: PMID:26251307
  description: >-
    Knock-in of the Japanese founder variant PROS1 p.Lys196Glu ("PS Tokushima")
    into the endogenous mouse Pros1 locus. Mice grow normally with normal protein
    S antigen but reduced APC-cofactor activity and exacerbated venous thrombosis.
  modeled_mechanisms:
  - target: Reduced Protein S Cofactor Activity
    relationship: RECAPITULATES
    fidelity: MODERATE
    description: >-
      Reproduces a qualitative (Type II-like) defect: normal protein S antigen
      with selectively reduced APC-cofactor activity, and increased susceptibility
      to venous thrombosis.
    limitations: >-
      Mouse plasma has no detectable protein S TFPI-cofactor activity, so this
      model cannot test whether K196E dissociates the APC-cofactor from the
      TFPI-cofactor pathway; the model also does not aggravate ischemic stroke.
    readouts:
    - name: Plasma APC-cofactor activity
      target: Reduced Protein S Cofactor Activity
      direction: DECREASED
      interpretation: >-
        The K196E mutant retains normal antigen but has selectively reduced APC
        anticoagulant cofactor activity - the molecular correlate of the reduced
        cofactor node.
      evidence:
      - reference: PMID:26251307
        reference_title: Exacerbated venous thromboembolism in mice carrying a protein S K196E mutation.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "the purified PS-K196E mutant had 49% to 60% of normal PS APC cofactor activity."
        explanation: Quantifies the selective reduction in APC-cofactor activity of the K196E protein.
    - name: Venous thrombosis susceptibility
      target: Reduced Protein S Cofactor Activity
      direction: INCREASED
      interpretation: >-
        K196E and heterozygous PS-deficient mice form larger venous thrombi and
        die more from induced pulmonary embolism than wild-type mice.
      evidence:
      - reference: PMID:26251307
        reference_title: Exacerbated venous thromboembolism in mice carrying a protein S K196E mutation.
        supports: SUPPORT
        evidence_source: MODEL_ORGANISM
        snippet: "Mice carrying a protein S-K196E mutation or heterozygous protein S deficiency were more vulnerable to venous thrombosis than wild-type mice."
        explanation: Reports increased venous thrombosis susceptibility, grounding the exacerbated-VTE phenotype of this model.
  evidence:
  - reference: PMID:26251307
    reference_title: Exacerbated venous thromboembolism in mice carrying a protein S K196E mutation.
    supports: SUPPORT
    evidence_source: MODEL_ORGANISM
    snippet: "PS-K196E mice grew normally but had decreased activated protein C cofactor activity in plasma."
    explanation: Establishes the K196E knock-in as an informative model of a qualitative reduced-APC-cofactor defect.
discussions:
- discussion_id: ps_cofactor_pathway_partition
  kind: KNOWLEDGE_GAP
  attaches_to:
  - pathophysiology#Reduced Protein S Cofactor Activity
  prompt: >-
    How much of protein S's in vivo anticoagulant effect in human hereditary
    deficiency is mediated through the APC-cofactor pathway versus the
    APC-independent TFPI-cofactor pathway, and does this partition differ across
    Type I/II/III subtypes and disease severity?
  rationale: >-
    Protein S has two mechanistically distinct anticoagulant cofactor roles (APC
    and TFPI). The global Pros1-/- model shows an aPC-independent component of
    accelerated thrombin generation (animal_models#Global Pros1 knockout mouse
    (Pros1-/-)), and the p.Lys196Glu knock-in model selectively reduces
    APC-cofactor activity (animal_models#Protein S K196E (Tokushima) knock-in
    mouse). But the K196E model cannot resolve the partition, because protein S
    TFPI-cofactor activity is not detectable in mouse plasma; the human claim of
    preserved TFPI-cofactor activity in K196E rests on human/biochemical data.
    The relative contribution of the two pathways in human hereditary deficiency,
    and its dependence on ISTH Type I/II/III subtype and severity, is unresolved.

📚

References & Deep Research

Deep Research

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Evaluations and curation notes (1)

Create: Protein S Deficiency · 2026-09-03T15:29:58Z · View source

De-novo curation of PROS1-driven hereditary protein S deficiency (THPH5; MONDO:0012868) as a distinct single-gene Mendelian thrombophilia, kept separate from the general Thrombophilia umbrella entry. Modeled the APC/TFPI cofactor loss pathophysiology chain (Reduced Protein S Cofactor Activity -> Unopposed Thrombin Generation -> Venous Thrombus Formation), conforming to the thrombogenesis module at the coagulation-cascade and fibrin-platelet-thrombus nodes, plus a warfarin-induced transient anticoagulant depletion branch. Curated has_subtypes Type I/II/III (ISTH), phenotypes (DVT, PE, neonatal purpura fulminans, reduced protein S activity, warfarin-induced skin necrosis), PROS1 genetics (AD incomplete penetrance and severe AR biallelic form), structured prevalence (mild congenital ~1/500, blood-donor 0.03-0.13%, Japanese 0.48-0.63%), free-vs-total protein S diagnostic assay, anticoagulation treatment (warfarin/rivaroxaban with heparin-bridged initiation), estrogen environmental second-hit, and the platelet-specific Pros1 knockout mouse model. Deep research run with claude_code provider; all evidence snippets verified as exact substrings against cached references (PMID:42429079, 40429442, 41180656, 9885367, 24144709, DOI:10.1182/blood.2019003630). Validated green: just validate, validate-terms, count-verified-snippets, check-causal-targets, check-duplicate-keys, check-entity-refs, check-qualifier-terms, check-environmental-evidence, check-enum-values, and authoritative validate-disorders.

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Protein S Deficiency: Comprehensive Research Report

claude-haiku-4-5-20251001, claude-sonnet-5 36 citations 2026-09-03T15:07:49.212521

Protein S Deficiency: Comprehensive Research Report

1. Disease Information

Overview. Protein S deficiency is an inherited or acquired thrombophilia caused by reduced plasma levels or functional activity of protein S, a vitamin K–dependent plasma glycoprotein that acts as a non-enzymatic cofactor for the anticoagulant proteins activated protein C (APC) and tissue factor pathway inhibitor (TFPI). Deficiency impairs down-regulation of the coagulation cascade, producing a hypercoagulable state manifesting predominantly as venous thromboembolism (VTE) — deep vein thrombosis (DVT), pulmonary embolism (PE), and superficial thrombophlebitis. A rare, severe homozygous/compound-heterozygous form causes neonatal purpura fulminans, a life-threatening disseminated microvascular thrombosis syndrome (StatPearls, NCBI Bookshelf NBK544344).

Key identifiers: - OMIM (gene): 176880 — PROS1 (protein S) - OMIM (phenotype, autosomal dominant/heterozygous): #612336 — Thrombophilia due to Protein S Deficiency, Autosomal Dominant (THPH5) (OMIM 612336) - OMIM (phenotype, autosomal recessive/severe): #614514 — Thrombophilia due to Protein S Deficiency, Autosomal Recessive (THPH6) (OMIM 614514) - Orphanet: ORPHA:743 — Severe hereditary thrombophilia due to congenital protein S deficiency (Orphanet 743) - MONDO: MONDO:0002304 - Disease Ontology: DOID:2451 - HPO (phenotype term): HP:0004855 (Protein S deficiency) - ICD-10-CM: D68.59 (Other primary thrombophilia — used for hereditary protein S deficiency) - Gene locus:* PROS1, chromosome 3q11.1 (HGNC:9457)

Synonyms: PS deficiency; hereditary/congenital protein S deficiency; THPH5 (dominant form); THPH6 (recessive/severe form); "protein S Tokushima" for the Japanese K155E/K196E variant designation.

Evidence base note: Much of the epidemiological and clinical literature derives from aggregated case-series, thrombophilia-clinic cohorts, and family/kindred studies rather than large population-representative EHR datasets — an important caveat given the assay/pre-analytical variability discussed in Section 10.

2. Etiology

Causal factors

Protein S deficiency arises from two broad mechanisms:

Congenital (genetic): Heterozygous or homozygous/compound-heterozygous pathogenic variants in PROS1. Over 200–300+ distinct PROS1 mutations have been catalogued (StatPearls cites >200; other reviews cite >300), including missense variants (most common), nonsense variants, small insertions/deletions, splice-site variants, and large deletions spanning one or multiple exons (ClinVar Miner; Human Genome Variation 2024). Most loss-of-function mutations produce premature stop codons and truncated, non-secreted or non-functional protein.
Acquired: Reduced protein S levels/activity secondary to another physiologic or pathologic state — vitamin K antagonist (warfarin) therapy, vitamin K deficiency, liver disease, nephrotic syndrome (urinary protein loss), disseminated intravascular coagulation (DIC), pregnancy, oral contraceptive/estrogen or hormone-replacement therapy, systemic lupus erythematosus, HIV infection, chronic/acute infection, and myeloproliferative disorders (StatPearls; Medscape overview).

Genetic risk factors

Causal PROS1 variants — dominant heterozygous variants cause the common, milder Type I/III phenotype; biallelic (homozygous or compound heterozygous) variants cause the severe neonatal form.
Founder/population-specific variant: PROS1 c.586A>G (p.Lys196Glu, "K196E"/legacy "K155E," known as "protein S Tokushima") is essentially restricted to Japanese populations, present in ~1.8% of Japanese individuals, and confers an odds ratio of 3.7–8.6 for VTE; it has not been found in Chinese, Korean, or Caucasian populations (racial-differences PMC7695562; PLOS ONE 2015).
Combined/modifier genetic factors: Co-inheritance of Factor V Leiden (FVL) with PROS1 deficiency is well documented and synergistically increases thrombosis risk (see Section 9).

Environmental / acquired risk factors

Immobility, surgery, trauma, pregnancy/puerperium, estrogen-containing contraceptives or HRT, and long-haul travel are documented precipitants; a large kindred study found that although these factors were common, "almost half of the events were spontaneous" (ClinVar/OMIM search summary; Annals of Internal Medicine 1998).

Protective factors

No specific genetic or environmental protective variant/exposure for protein S deficiency was identified in the literature searched; general VTE risk-reduction measures (avoidance of estrogen therapy, maintaining mobility, prophylactic anticoagulation during high-risk periods) apply, but the review found no dedicated protective-allele literature analogous to, e.g., Factor V Leiden's population-genetics protective hypotheses.

Gene–environment interaction

The clearest documented interaction is with exogenous estrogen (oral contraceptives, HRT, pregnancy), which itself lowers free protein S levels physiologically and is superimposed on a genetically reduced baseline, precipitating clinical thrombosis in previously asymptomatic carriers ("Protein S levels decrease in pregnancy and can fall into the abnormal-low laboratory range" — Cleveland Clinic; StatPearls).

3. Phenotypes

Phenotype categories and suggested HPO terms

Phenotype	Type	Suggested HPO term
Deep vein thrombosis	Sign/laboratory-imaging	HP:0002625 (Peripheral thrombosis) / HP:0004936 (Deep venous thrombosis, if available)
Pulmonary embolism	Sign	HP:0004942 (Pulmonary embolism)
Superficial thrombophlebitis	Sign	HP:0025138 (Phlebitis) or related
Purpura fulminans (neonatal)	Sign, severe/congenital	HP:0025282 (Purpura fulminans)
Recurrent pregnancy loss	Sign	HP:0032449 (Recurrent miscarriage)
Cerebral venous sinus thrombosis	Sign, rare-site	HP:0006956 (Cerebral venous thrombosis, if modeled)
Reduced Protein S activity/antigen	Laboratory abnormality	HP:0004855 (Protein S deficiency)
Warfarin-induced skin necrosis	Sign, treatment complication	(no direct HP term; model as adverse-drug-reaction phenotype)
Post-thrombotic syndrome	Sign, sequela	HP:0025490 (if modeled)

Characteristics

Onset: Two clearly separable onset patterns —
Heterozygous/mild congenital or acquired disease: adult-onset, with median age at first VTE around 29 years in some cohorts; "almost half of all individuals with protein S deficiency become symptomatic before age 55" (StatPearls).
Homozygous/compound heterozygous severe disease: neonatal onset, "manifests several hours to days after birth, with purpura fulminans or massive venous thrombosis" (NORD/GARD).
Severity: Highly variable in the heterozygous form (many carriers remain asymptomatic lifelong — see penetrance below); uniformly severe and life-threatening in the biallelic neonatal form.
Progression: Recurrent/relapsing pattern typical for heterozygous VTE; the neonatal form is acute and rapidly progressive without emergency plasma replacement.
Frequency of specific manifestations among symptomatic patients: DVT ~74%, superficial thrombophlebitis ~72%, PE ~38% (may co-occur); "venous thromboembolism occurring in approximately 50–60% of people with protein S deficiency" who are carriers over their lifetime; involvement of cerebral, visceral, mesenteric, or axillary veins is comparatively rare (Cleveland Clinic; StatPearls).
Penetrance: Among heterozygous carriers, roughly 50% develop venous thromboembolism in their lifetime; 50% remain asymptomatic (StatPearls).
Quality of life impact: Not extensively quantified in disease-specific QOL instruments in the literature surveyed; morbidity relates chiefly to recurrent VTE, post-thrombotic syndrome, chronic anticoagulation burden/bleeding risk, and (in severe cases) neurodevelopmental sequelae from neonatal thrombosis/hemorrhage (e.g., a reported case with in utero retinal vessel thrombosis and blindness — OMIM 614514).

4. Genetic / Molecular Information

Causal gene

PROS1 (Protein S), HGNC:9457, chromosome 3q11.1. OMIM *176880.

Variant classification and types

Type of variants: predominantly missense; also nonsense, small indels, splice-site, and large exonic deletions (ClinVar Miner).
A 2024–2025 systematic reanalysis of 276 patients with suspected hereditary PS deficiency identified 48 distinct variants across 101 patients — 27 previously reported, 11 present in ClinVar/dbSNP without prior clinical categorization, and 10 entirely novel (PubMed 42079676).
Specific examples: p.Thr78Met (ClinVar RCV000197958), p.Met640Thr (RCV001211450), p.Arg355Cys (RCV000022724), p.Ser501Pro (RCV000205145), p.Val606Ile (RCV000206212), p.Leu584Arg (mesenteric/portal vein thrombosis case, PMC10682651), and c.602-2delA (splice acceptor mutation, exon 7, in a Polish VTE patient, PMC7558706).
A stop-codon read-through variant (wobble-position A→T transversion) extends the protein by 14 amino acids before reaching a novel stop codon, illustrating an unusual loss-of-function mechanism.
Founder variant: PROS1 c.586A>G p.Lys196Glu ("K196E"/"K155E," "PS Tokushima") — Japan-specific, ~1.8% allele carriage, associated with Type II-pattern deficiency (normal antigen, reduced APC-cofactor functional activity) (ClinVar RCV000014246; PMC6178719).

Functional consequence / laboratory classification (ISTH system)

Three recognized subtypes, based on total antigen, free antigen, and functional (cofactor) activity: - Type I: ↓ total protein S antigen, ↓ free antigen, ↓ activity (quantitative deficiency). - Type II: normal antigen levels (total and free), ↓ functional activity (qualitative/dysfunctional protein — e.g., K196E "PS Tokushima"). - Type III: normal total antigen, ↓ free antigen, ↓ activity (abnormal partitioning between free and C4BP-bound forms). Type II is rare; Types I and III are the most common phenotypes clinically encountered (StatPearls).

Modifier genes

Factor V Leiden (F5 R506Q) — most clinically significant co-inherited modifier; markedly amplifies thrombotic risk when combined with PROS1 deficiency (Section 9).

Population allele frequency

Founder K196E variant carrier frequency ~1.8% in Japan (estimated ~9,440 individuals homozygous in the Japanese population) (PLOS ONE).
General-population heterozygous ("partial") deficiency prevalence: 0.16–0.21% (Orphanet); blood-donor cohort estimates 0.03–0.13%, rising to 3–5% among patients selected for recurrent thrombosis/strong family history (StatPearls).

Epigenetics / chromosomal abnormalities

No disease-specific epigenetic mechanism (DNA methylation/histone modification) or recurrent chromosomal structural abnormality was found reported for PROS1-related deficiency in the literature surveyed; the genetic architecture is single-gene Mendelian (with digenic/oligogenic modification by FVL).

5. Environmental Information

Pharmacologic/hormonal exposures: Vitamin K antagonists (warfarin) directly suppress synthesis of functional (carboxylated) protein S; estrogen-containing oral contraceptives, hormone replacement therapy, and pregnancy physiologically lower free protein S and unmask latent deficiency (Cleveland Clinic).
Nutritional/vitamin status: Vitamin K deficiency (malabsorption, dietary insufficiency, antibiotic-associated) reduces γ-carboxylation of protein S, lowering functional activity.
Hepatic and renal disease: Liver disease reduces synthetic production; nephrotic syndrome causes urinary loss of protein S (a smaller, more easily lost molecule relative to some other coagulation factors).
Infectious/inflammatory triggers: Acute infection and DIC consume and lower protein S acutely; chronic infections (e.g., HIV) are associated with acquired deficiency.
Autoimmune disease: Systemic lupus erythematosus is associated with acquired protein S deficiency, sometimes compounded by antiphospholipid antibodies.
No specific infectious pathogen causally produces the inherited disorder; infection functions as an acquired-deficiency trigger and precipitant of thrombosis, not an etiological agent of the genetic disease itself.

6. Mechanism / Pathophysiology

Ordered causal chain

A heterozygous (or homozygous/compound heterozygous) loss-of-function variant in PROS1 → reduced synthesis, secretion, or functional activity of protein S in hepatocytes and (to a lesser extent) endothelial cells and megakaryocytes.
Reduced circulating free/functional protein S → diminished APC-cofactor activity, because protein S normally accelerates activated protein C (APC)-mediated proteolytic inactivation of factors Va and VIIIa by roughly 10-fold (a γ-carboxyglutamic-acid–dependent function requiring the Gla domain) (ASH Blood 2011).
In parallel, reduced protein S → diminished TFPIα cofactor function: the Laminin-G1 (LG1) domain of protein S binds TFPIα's K3 domain and enhances TFPIα-mediated inhibition of factor Xa 4- to 10-fold by promoting TFPIα association with phospholipid membrane surfaces (AHA journals ATVB 2008; Science Advances 2024). A 2024 in vivo study found "TFPIα anticoagulant function is highly dependent on protein S in vivo," underscoring this as a major, independent (APC-free) anticoagulant pathway.
Loss of these two cofactor functions, plus loss of protein S's direct inhibition of the intrinsic tenase (FVIIIa–FIXa) and prothrombinase (FVa–FXa) complexes, leads to failure to down-regulate thrombin generation, particularly at sites of vascular injury.
Unchecked thrombin generation → excess fibrin formation and platelet activation, tipping local hemostatic balance toward pathological clot formation → venous thrombus formation (most often in the deep veins of the lower extremity).
A propagating or embolizing thrombus → pulmonary embolism, or (in unusual/high-risk sites) cerebral venous sinus, mesenteric, portal, or axillary vein thrombosis.
In the rare biallelic/severe form, near-total absence of protein S (plasma levels <1% reported in purpura-fulminans infants) → diffuse microvascular thrombosis in skin and viscera within hours to days of birth, producing purpura fulminans, DIC, and in some cases intracranial hemorrhage or in-utero ocular vascular thrombosis causing blindness (OMIM 614514; PubMed 2231208).
Branch — Warfarin-induced skin necrosis: in a protein-deficient patient started on warfarin without heparin bridging, the drug's early, more rapid suppression of already-low protein C/protein S relative to slower-acting procoagulant factor depletion transiently amplifies the pre-existing procoagulant tilt → microvascular thrombosis in skin/subcutaneous fat, producing painful purpuric/necrotic skin lesions; this is a recognized (though for protein S specifically, less common than for protein C deficiency) risk. ("Warfarin-induced skin necrosis has been associated with protein C deficiency but only rarely reported in patients with a deficiency of protein S" — PubMed 1427456; PubMed 9885367).
Branch — Combined defect amplification: co-inheritance of Factor V Leiden (which itself impairs APC-mediated FVa inactivation) with protein S deficiency compounds the loss of APC-pathway regulation through two independent mechanisms simultaneously, synergistically (not merely additively) raising thrombotic risk (Section 9) — a demonstrated "two-hit" model.

Molecular pathways

KEGG/Reactome-relevant pathways: Complement and coagulation cascades (KEGG hsa04610); Regulation of Complement cascade / Protein C activation; Formation of Fibrin Clot (Clotting Cascade) in Reactome; the APC-Protein S and TFPI-Protein S anticoagulant sub-pathways.

Protein structure/dysfunction

Protein S is a multidomain, vitamin K–dependent glycoprotein comprising: - An N-terminal Gla domain (10 γ-carboxyglutamic acid residues, vitamin K–dependently modified — required for phospholipid membrane binding and, notably, for APC-cofactor activity via a specific Gla residue) (ASH Blood 2011). - A thrombin-sensitive region (TSR). - Four tandem EGF-like domains. - A C-terminal SHBG-like domain containing two Laminin G-type (LG1, LG2) domains, together constituting >55% of the mature protein's length; the LG1 domain mediates TFPIα cofactor activity and is competitively regulated by C4BP binding, while the first LG domain also binds/activates the receptor tyrosine kinase Tyro3 for non-hemostatic (efferocytosis/immune) signaling (Blood Advances 2022; ScienceDirect 2022). - C4b-binding protein (C4BP) partitioning: ~60–70% of circulating protein S is bound in a high-affinity 1:1 complex with the C4BP β-chain (via both LG domains) and is anticoagulantly inactive; only the ~30–40% free fraction is functionally active as an APC/TFPI cofactor. This is the molecular basis of Type III deficiency, in which free-fraction partitioning is abnormal despite normal total antigen.

Cellular processes / tissue-level consequences

Endothelial dysfunction and loss of local anticoagulant surface regulation at sites of venous stasis/injury; downstream fibrin deposition and, in purpura fulminans, dermal/subcutaneous ischemic necrosis from occlusive microvascular thrombosis.

Advanced/omics findings

The literature reviewed did not surface disease-specific transcriptomic, proteomic, or single-cell datasets specific to PROS1 deficiency beyond conventional coagulation-assay and genetic-variant characterization; most mechanistic insight comes from biochemical/structural studies of protein S domains and from murine genetic models (Section 15).

Suggested ontology terms: GO:0030195 (negative regulation of blood coagulation); GO:0072378 (blood coagulation, fibrin clot formation); GO:0031093 (platelet alpha granule lumen, n/a — not directly relevant); CL:0000182 (hepatocyte, site of synthesis); UBERON:0001997 (vein, site of thrombosis); CHEBI:29108 (calcium ion, cofactor for Gla-domain phospholipid binding, if relevant to a molecular node).

7. Anatomical Structures Affected

Organ/system level: Cardiovascular system — primarily the venous circulation. Primary sites: deep veins of the lower extremities (UBERON:0001474/lower limb vein), pulmonary vasculature (embolic secondary involvement), superficial veins. Less common: cerebral venous sinuses, portal/mesenteric veins, axillary veins. In neonatal purpura fulminans, skin/subcutaneous microvasculature is primarily affected, with potential multi-organ (renal, cerebral, ocular) involvement due to disseminated microthrombosis.
Tissue/cell level: Vascular endothelium (site of anticoagulant cofactor activity), hepatocytes (primary site of protein S synthesis; CL:0000182), platelets (secondary involvement via thrombus formation), dermal/subcutaneous microvasculature (purpura fulminans).
Subcellular level: Not classically compartment-specific for pathology (protein S is a secreted plasma protein); relevant GO Cellular Component for wild-type biology: GO:0005615 (extracellular space), GO:0070062 (extracellular exosome, for some assay contexts).
Localization: Predominantly bilateral or unilateral lower-extremity DVT; PE is typically bilateral/multifocal in the pulmonary vasculature. Purpura fulminans lesions are typically symmetric and affect distal extremities, buttocks, and trunk.

8. Temporal Development

Onset pattern (heterozygous/mild form): Adult-onset, though can occur in adolescence; median age at first VTE reported around 29 years in some cohort analyses; roughly half of carriers become symptomatic before age 55.
Onset pattern (severe homozygous/compound heterozygous form): Neonatal, typically within hours to days of birth (purpura fulminans, massive venous thrombosis, sometimes with evidence of in-utero thrombotic events such as ocular/retinal vessel occlusion).
Progression: Heterozygous disease follows an episodic/recurrent course (discrete VTE events, sometimes provoked, sometimes spontaneous) rather than a steadily progressive one; recurrence is common, especially with inadequate anticoagulation duration or continued risk-factor exposure. The neonatal form is acute and rapidly progressive, requiring emergency plasma-product replacement to prevent death.
Disease course pattern: Relapsing rather than continuously progressive for the common form; post-thrombotic syndrome and chronic venous insufficiency can represent a chronic sequela.
Critical periods / windows of vulnerability: Pregnancy/puerperium (antepartum VTE risk 0.9%, postpartum risk 4.2% in protein S–deficient women — high-risk thrombophilia category), immediate postoperative/post-trauma period, immobilization, initiation of estrogen therapy, and initiation of warfarin without heparin bridging (skin-necrosis window, typically days 3–8 of warfarin therapy based on general VKA-necrosis literature).

9. Inheritance and Population

Epidemiology

Prevalence, partial (heterozygous) deficiency: 0.16–0.21% general population (Orphanet); blood-donor screening estimates 0.03–0.13%.
Prevalence, severe (homozygous/compound heterozygous) deficiency: Unknown precisely, but probably comparable to severe protein C deficiency (~1/500,000) (Orphanet ORPHA:743).
Prevalence among thrombophilia/VTE-referral cohorts: 3–5% (StatPearls); up to 12.7% in Japanese thrombosis patients when the K196E founder variant is included.
Neonatal purpura fulminans (combined protein C + protein S causes): ~1 in 1 million live births.

Inheritance pattern

Autosomal dominant for the common heterozygous/partial deficiency (OMIM #612336, THPH5) — incomplete penetrance (~50%).
Autosomal recessive for the severe homozygous/compound heterozygous form (OMIM #614514, THPH6) — "very rare and severe hematologic disorder resulting in thrombosis and secondary hemorrhage usually beginning in early infancy" (OMIM 614514).

Penetrance / expressivity

Penetrance in heterozygotes ~50% (variable, incomplete).
Expressivity is markedly variable — from asymptomatic carrier status to recurrent life-threatening VTE — modified by co-inherited thrombophilic factors (see below), hormonal exposures, and other acquired risk factors.

Genetic anticipation / germline mosaicism

No genetic-anticipation phenomenon is described (not a repeat-expansion disorder).
Germline mosaicism has been reported: "First report of inherited protein S deficiency caused by paternal PROS1 mosaicism" (Haematologica), relevant for recurrence-risk counseling when a de novo–appearing variant is found in an affected child.

Founder effects / population variation

PROS1 K196E (K155E, "PS Tokushima") is a Japan-specific founder variant, absent in Chinese, Korean, and Caucasian populations, accounting for 9–30% of protein S abnormalities detected in Japan.
Protein S deficiency overall is reported to be "5 to 10 times more common in Japanese populations than in whites," with general-population prevalence of 0.48–0.63% in Japan vs. 12.7% in Japanese thrombosis patients (StatPearls).

Consanguinity

Biallelic (severe/recessive) disease is more likely in consanguineous unions, consistent with autosomal recessive inheritance, though this review did not find a dedicated consanguinity-specific epidemiologic study for PROS1.

Sex and demographic distribution

Men demonstrate higher baseline protein S antigen levels than women.
Protein S levels rise with age in women (hormonal influence) but remain relatively stable in men across adulthood — a key pre-analytical consideration for diagnostic interpretation (StatPearls).

Digenic/combined-defect epidemiology (Factor V Leiden + Protein S deficiency)

In sibships segregating both PROS1 deficiency and Factor V Leiden, 80% of individuals carrying both defects were symptomatic, versus a much lower rate with either defect alone (PubMed 9607123).
Mean age at first thrombosis: 18.4 years (combined defect) vs. 32.6 years (single defect) — "significantly lower... thrombosis-free survival time was significantly shorter" (PubMed 8584987).
Among symptomatic PROS1-deficient probands, FVL prevalence was 38% (vs. general-population FVL prevalence of ~3–5% in most European populations), consistent with strong ascertainment/selection and a synergistic "two-hit" thrombosis model (Blood 1998, 150-family study).

10. Diagnostics

Laboratory tests

Free protein S antigen (immunoturbidimetric/ELISA): considered "the most reliable way of diagnosing the deficiency" because it reflects the functionally active, non-C4BP-bound fraction.
Total protein S antigen (ELISA): detects Type I deficiency well but cannot detect Type II or Type III deficiency, since these have normal total antigen.
Functional (clotting-based) protein S activity assay: measures APC-cofactor–dependent prolongation of clotting time; detects all three types but is technically the most failure-prone assay.
Key pre-analytical/assay pitfalls:
Factor V Leiden causes falsely low functional protein S results in older clotting-based assays (interference); newer assays with plasma-dilution protocols mitigate this.
Levels are altered by pregnancy, oral contraceptives/HRT, acute-phase reaction/inflammation, acute thrombosis itself, vitamin K deficiency, warfarin therapy, and liver disease — testing should be deferred to a stable, non-acute, non-anticoagulated, non-pregnant state where possible.
Age- and sex-adjusted reference ranges are essential given the physiologic variation described above.

ISTH diagnostic criteria (2021 SSC recommendations)

Diagnosis requires persistently reduced plasma protein S concentration and/or activity below the reference interval, confirmed on at least two abnormal results obtained ≥4 weeks apart under appropriate testing conditions (i.e., outside acute thrombosis, pregnancy, and anticoagulation) (Marlar et al., J Thromb Haemost 2021).

Genetic testing

PROS1 sequencing (Sanger or NGS-based single-gene test or thrombophilia gene panel) plus deletion/duplication analysis (MLPA or similar) to detect large exonic deletions.
Available as a clinical test via commercial/academic laboratories (e.g., listed in NCBI GTR) and useful for confirming ambiguous phenotypic results, cascade/family testing, and prenatal or newborn diagnosis in families with known severe (biallelic) disease.
The ISTH maintains/has maintained a PROS1 mutation database resource to support variant interpretation.
ACMG/AMP classification: PROS1 variants are curated in ClinVar with standard pathogenic/likely pathogenic/VUS/likely benign/benign tiers; as above, a 2024–2025 reanalysis found a substantial fraction of variants in suspected-deficiency patients were novel or previously unclassified, underscoring ongoing curation need.

Imaging / functional / other studies

Standard VTE-diagnostic imaging applies (compression ultrasonography for DVT, CT pulmonary angiography for PE, MR venography for cerebral venous sinus thrombosis) — these are general VTE-diagnostic tools, not protein S–specific.
No disease-specific biopsy/histopathology test exists; skin biopsy in warfarin-induced necrosis may show microvascular thrombosis with hemorrhagic necrosis, supportive but non-specific.

Differential diagnosis

Antiphospholipid syndrome, antithrombin deficiency, Factor V Leiden/APC resistance, protein C deficiency, prothrombin G20210A mutation, paroxysmal nocturnal hemoglobinuria, and malignancy-associated hypercoagulability — all must be distinguished, and acquired causes of low protein S (pregnancy, vitamin K deficiency, oral contraceptives, hepatic dysfunction, chronic infection) must be excluded before assigning a congenital diagnosis (StatPearls).

Screening

No population-based newborn screening program for protein S deficiency exists; testing is generally targeted (unprovoked/recurrent VTE, VTE at young age or unusual site, strong family history, neonatal purpura fulminans) and cascade family testing is used once a proband's causal variant is identified.

11. Outcome/Prognosis

Heterozygous/mild disease: Generally good prognosis with appropriate anticoagulation; "little evidence suggests that thrombophilia related to protein S deficiency results in a deteriorated prognosis for VTE" compared with VTE from other causes, though recurrence risk and chronic anticoagulation-associated bleeding risk represent ongoing morbidity (StatPearls).
Severe (biallelic) neonatal disease: Poor prognosis without aggressive, sustained replacement therapy; complications of repeated plasma infusion (fluid overload) contribute to a historically high infant mortality rate; long-term outcome data remain limited.
Recurrence: Recurrent VTE and post-thrombotic syndrome (chronic venous insufficiency, pain, edema, skin changes) are the dominant morbidity drivers in surviving heterozygous patients; a documented case series highlights recurrent DVT/PE "despite optimal anticoagulation therapies" (PMC11180491).
Prognostic modifiers: Co-inherited Factor V Leiden substantially worsens prognosis (earlier onset, shorter thrombosis-free interval, higher penetrance — Section 9); pregnancy is a high-risk period (antepartum VTE 0.9%, postpartum 4.2%).
Mortality: Disease-specific population mortality statistics were not identified in the sources reviewed beyond the neonatal-purpura-fulminans context; adult heterozygous disease mortality is primarily related to PE and anticoagulation-related bleeding rather than the deficiency itself.

12. Treatment

Pharmacotherapy (acute/chronic VTE management)

Initial/acute phase: Intravenous unfractionated heparin or subcutaneous low-molecular-weight heparin (LMWH) for a minimum of ~5 days.
Maintenance: Vitamin K antagonist (warfarin) or a direct oral anticoagulant (DOAC, e.g., apixaban, rivaroxaban). DOACs are increasingly favored for efficacy/safety, with warfarin reserved for specific situations (extremes of body weight, large proximal clot burden, massive/submassive PE) — suggest NCIT:C15986 (Pharmacotherapy) as treatment_term with therapeutic_agent bound to CHEBI (e.g., warfarin CHEBI:10033, apixaban CHEBI:66401) or NCIT drug terms.
Duration: Standard 3–6 months post-VTE; extended/lifelong anticoagulation for life-threatening events, unusual/multiple-site thrombosis, or recurrent unprovoked VTE; shorter courses acceptable when a strong transient provoking factor (surgery/trauma) was present without unusual features.
Warfarin-necrosis avoidance: Heparin bridging during warfarin initiation is critical in protein C/S–deficient patients to avoid the transient hypercoagulable "warfarin necrosis" window; if necrosis occurs, heparin is reinstituted and warfarin may be cautiously restarted at low dose with overlap once the acute event resolves (PubMed 1427456).

Advanced/replacement therapeutics (severe congenital form)

Fresh frozen plasma (FFP): first-line emergency replacement therapy for neonatal purpura fulminans, typically dosed every 8–12 hours and titrated to clinical response.
Plasma-derived protein C/protein S concentrate: an emerging, more targeted replacement option available at some centers, though access remains limited (NORD/GARD; StatPearls).
Liver transplantation has been used as definitive therapy for severe homozygous protein C deficiency (analogous rationale could extend to protein S, though this review found the direct evidence base specifically for protein S transplantation to be sparse — flagged as a gap).

Surgical/interventional

No protein S–deficiency–specific surgical intervention; standard VTE-related interventions (IVC filter in select cases, thrombectomy for massive PE/limb-threatening DVT) apply per general VTE guidelines.

Supportive/rehabilitative

Compression therapy for post-thrombotic syndrome, physical therapy/mobility rehabilitation, and wound care for purpura fulminans/skin necrosis lesions.

Pregnancy-specific management

LMWH is preferred throughout pregnancy (does not cross the placenta); warfarin is contraindicated for teratogenicity; specific caution is advised in the first trimester and after 36 weeks gestation, transitioning to LMWH over warfarin in those windows to minimize fetal/maternal bleeding risk. Protein S deficiency is classified as a high-risk thrombophilia in pregnancy risk-stratification schemes.

Prophylaxis in asymptomatic carriers

Risk-adapted prophylactic anticoagulation is recommended around known high-risk exposures (surgery, prolonged immobilization, long-haul travel, pregnancy) rather than universal indefinite anticoagulation for asymptomatic carriers.

Experimental/trial landscape

The literature surveyed did not identify active gene-therapy, RNA-based, or novel targeted-biologic trials specific to protein S deficiency (unlike, e.g., hemophilia); management remains centered on conventional and plasma-derived anticoagulant/replacement approaches. (This is a notable gap suitable for just verify-datasets/ClinicalTrials.gov confirmation before KB citation.)

Treatment outcomes / adverse events

Standard anticoagulant bleeding risk applies; cumulative bleeding risk increases with extended/lifelong therapy duration.
Warfarin-induced skin necrosis is an uncommon but serious adverse event more classically linked to protein C deficiency, with rare case reports in protein S deficiency.

13. Prevention

Primary prevention: Avoidance of estrogen-containing contraceptives/HRT in known carriers; prophylactic anticoagulation around high-risk exposures (surgery, immobilization, pregnancy, travel).
Secondary prevention: Prompt recognition and treatment of first VTE event to reduce recurrence and post-thrombotic syndrome; screening of family members of an index case via cascade testing.
Tertiary prevention: Extended-duration anticoagulation in patients with life-threatening or recurrent/unusual-site thrombosis to prevent further events; compression therapy to limit post-thrombotic syndrome progression.
Genetic/prenatal counseling: Recommended for families with known severe (biallelic) disease, particularly given documented germline mosaicism and the life-threatening neonatal phenotype; carrier and prenatal testing can be offered in high-risk families once the familial PROS1 variant(s) are characterized.
Screening: No population-based newborn screening program exists; targeted screening is triggered by unprovoked or recurrent VTE at a young age, VTE at an unusual site, strong family history, or neonatal purpura fulminans.
Public health/behavioral: General VTE risk-reduction counseling (mobility, hydration during travel, smoking cessation given compounding vascular risk) applies but is not disease-specific.

14. Other Species / Natural Disease

No naturally occurring (spontaneous) animal model of protein S deficiency analogous to human PROS1 disease was identified in this review; by contrast, congenital protein C deficiency has been reported in a dog (PMC7255666), but an equivalent natural canine/feline protein S deficiency case was not found in the sources searched (OMIA-style entries for this specific condition were not located). This is a notable evidence gap — absence of identified reports, not confirmed absence of the condition in veterinary species.
Orthologous gene: Pros1 is conserved across mammals (mouse Pros1, NCBI Gene); no cross-species comparative pathology literature specific to naturally occurring disease was found.
Zoonotic potential: Not applicable — this is a non-infectious, genetic/acquired hemostatic disorder.

15. Model Organisms

Global Pros1 knockout mice: Complete (germline) Pros1 knockout is embryonic lethal, causing a coagulopathy and vascular dysgenesis phenotype — "Lack of Protein S in mice causes embryonic lethal coagulopathy and vascular dysgenesis" (JCI), directly paralleling the severe consequences of near-total human protein S loss (as in neonatal purpura fulminans) and confirming an essential, non-redundant role for protein S in vascular/hemostatic development.
Conditional (floxed) Pros1 knockout mice: Because global knockout is lethal, researchers generated a Cre-lox conditional floxed Pros1 allele and crossed it with multiple Cre-driver lines to achieve tissue-specific inactivation — pan-cellular, hepatocyte-specific, endothelial/hematopoietic-specific, and vascular smooth muscle cell (VSMC)-specific knockouts — revealing "dramatic but divergent phenotypes" across tissue compartments and clarifying the relative contributions of different cellular sources of protein S, analyzed alongside the related Axl/Gas6 receptor-ligand knockout mice (protein S's paralog Gas6 signals through the TAM receptor family, of which protein S itself also weakly engages Tyro3).
PS K196E (Tokushima) knock-in mouse: A mouse model carrying the human K196E mutation showed "exacerbated venous thromboembolism," directly demonstrating causality of this Japan-specific variant for thrombotic risk in vivo (Blood 2015) and confirming that the mutation "reduces its cofactor activity for APC but not for TFPI" — a mechanistically informative dissociation between the two protein S anticoagulant functions (PMC6178719).
Applications: These murine models have been central to establishing (a) the non-redundant, developmentally essential role of protein S in vascular integrity, (b) tissue-specific sourcing of functionally relevant plasma protein S, and (c) the mechanistic basis (APC- vs. TFPI-cofactor–selective loss) of specific human missense variants.
Limitations: Complete knockout lethality means no adult "null" mouse model exists for studying postnatal severe deficiency physiology directly; conditional models are needed, and cross-species differences in coagulation-factor regulation (e.g., mouse vs. human C4BP stoichiometry) may limit direct translational extrapolation.
Resources: MGI (Mouse Genome Informatics) carries the Pros1 gene and knockout allele records; IMPC/KOMP repositories may hold additional conditional-allele strains (not individually itemized in the sources retrieved here).

Summary of Key Evidence Gaps (flagged for curation)

No naturally occurring veterinary (dog/cat) model of protein S deficiency was located, despite a documented canine protein C deficiency case — worth a targeted OMIA search before asserting absence.
Disease-specific quality-of-life instrument data (EQ-5D/SF-36) specific to protein S deficiency were not found; QOL impact is inferred from general VTE/anticoagulation morbidity literature.
Active gene-therapy/RNA-therapeutic clinical trials specific to protein S deficiency were not identified — the therapeutic landscape remains conventional (anticoagulant/plasma replacement).
Precise disease-specific mortality/life-expectancy statistics (beyond neonatal purpura fulminans mortality risk) were not found in a single aggregated source; figures cited (e.g., annual VTE incidence 1.90%, median onset age 29) trace to StatPearls' synthesis rather than a single primary epidemiologic study, and should be traced to primary cohort sources before KB citation.
Liver transplantation as definitive therapy is documented for homozygous protein C deficiency; direct primary-literature support for protein S–specific transplantation outcomes was not retrieved and should not be assumed by analogy without confirmation.

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Discussions and Knowledge Gaps

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Phenotypes

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Biochemical Markers

Diagnosis

Prevalence

Animal Models

Source YAML

References & Deep Research

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Protein S Deficiency: Comprehensive Research Report

1. Disease Information

2. Etiology

Causal factors

Genetic risk factors

Environmental / acquired risk factors

Protective factors

Gene–environment interaction

3. Phenotypes

Phenotype categories and suggested HPO terms

Characteristics

4. Genetic / Molecular Information

Causal gene

Variant classification and types

Functional consequence / laboratory classification (ISTH system)

Modifier genes

Population allele frequency

Epigenetics / chromosomal abnormalities

5. Environmental Information

6. Mechanism / Pathophysiology

Ordered causal chain

Molecular pathways

Protein structure/dysfunction

Cellular processes / tissue-level consequences

Advanced/omics findings

7. Anatomical Structures Affected

8. Temporal Development

9. Inheritance and Population

Epidemiology

Inheritance pattern

Penetrance / expressivity

Genetic anticipation / germline mosaicism

Founder effects / population variation

Consanguinity

Sex and demographic distribution

Digenic/combined-defect epidemiology (Factor V Leiden + Protein S deficiency)

10. Diagnostics

Laboratory tests

ISTH diagnostic criteria (2021 SSC recommendations)

Genetic testing

Imaging / functional / other studies

Differential diagnosis

Screening

11. Outcome/Prognosis

12. Treatment

Pharmacotherapy (acute/chronic VTE management)

Advanced/replacement therapeutics (severe congenital form)

Surgical/interventional

Supportive/rehabilitative

Pregnancy-specific management

Prophylaxis in asymptomatic carriers

Experimental/trial landscape

Treatment outcomes / adverse events

13. Prevention

14. Other Species / Natural Disease

15. Model Organisms

Summary of Key Evidence Gaps (flagged for curation)

Sources