| Knowledge-base field | Curated summary | Ontology / evidence |
|---|---|---|
| Disease definition | Ultra-rare inherited bleeding disorder caused by reduced quantity or impaired function of coagulation factor II (prothrombin). Complete prothrombin absence has not been observed in humans and is considered incompatible with survival. | **MONDO:** MONDO:0013361. Reviews: DOI [10.1055/s-0029-1225759](https://doi.org/10.1055/s-0029-1225759), June 2009; DOI [10.3390/jcm6040045](https://doi.org/10.3390/jcm6040045), April 2017. (pqac-00000002, pqac-00000004) |
| Identifiers and synonyms | **Synonyms:** congenital factor II deficiency; hereditary factor II deficiency; congenital prothrombin deficiency; hypoprothrombinemia; dysprothrombinemia. **OMIM, Orphanet, MeSH, ICD-10/ICD-11:** exact identifiers were not verified in the gathered evidence and should be curated directly from those resources. | MONDO:0013361; disease-target entry in Open Targets. (pqac-00000001) |
| Epidemiology and inheritance | Estimated prevalence approximately **1 in 2,000,000** for severe homozygous/compound-heterozygous deficiency. Predominantly **autosomal recessive**, affecting both sexes; prevalence is higher where consanguinity is common. Penetrance and carrier frequency are not reliably quantified. | ClinGen classifies the **F2–disease** relationship as **Definitive** with AR inheritance. DOI [10.1016/j.thromres.2019.09.006](https://doi.org/10.1016/j.thromres.2019.09.006), December 2020. (pqac-00000001, pqac-00000003) |
| Causal gene and protein | **F2**, ENSG00000180210, encodes vitamin-K-dependent prothrombin, the zymogen of thrombin. The protein contains a signal peptide, propeptide, Gla domain, kringle 1 and 2 domains, and a serine-protease domain; factor Xa cleavage at Arg273 and Arg322 generates active thrombin. | **Target:** F2/coagulation factor II, thrombin; chromosome 11p11–q12. Suggested GO: blood coagulation (**GO:0007596**), fibrin clot formation (**GO:0072378**), proteolysis (**GO:0006508**). (pqac-00000001, pqac-00000004, pqac-00000007) |
| Biochemical subtypes | **Type I—hypoprothrombinemia:** factor II activity and antigen are both reduced. **Type II—dysprothrombinemia:** activity is reduced while antigen is normal or near normal. Activity-based severity used in reviews: **severe <5%**, **moderate 5–10%**, **mild >10%**. | Suggested phenotypic/laboratory concept: reduced coagulation factor II activity. Classification and thresholds derive mainly from expert reviews rather than validated prospective criteria. (pqac-00000004, pqac-00000013) |
| Representative pathogenic variants | Germline biallelic variants include missense, in-frame deletion, frameshift, splice-region, and other loss-of-function alleles. Examples include **Arg271Cys** with factor II activity **10.2%** and severe bleeding; **Ala362Thr (Prothrombin Vellore 1)** near catalytic His363/Cys364; Arg−1Gln affecting the furin-recognition sequence; Arg457Gln enriched among reported Puerto Rican cases; and compound Prothrombin Edmonton R−4Q plus a deletion. Population allele frequencies and current ClinVar classifications were not established here and require variant-level curation. | Primary molecular study: DOI [10.1111/j.1538-7836.2005.01402.x](https://doi.org/10.1111/j.1538-7836.2005.01402.x), July 2005. Historical F2 variant PMIDs include **1421398, 1349838, 3567158, 3801671, 22028381, 6405779, 1354985, 7792730, 3771562, 2719946**. (pqac-00000008, pqac-00000010, pqac-00000012) |
| Hallmark phenotypes | Variable, lifelong bleeding diathesis: easy bruising (**HP:0000978**), hematoma (**HP:0001020**), epistaxis (**HP:0000421**), oral/gingival bleeding (**HP:0000225**, suggested), menorrhagia (**HP:0000132**), prolonged postsurgical bleeding (**HP:0004846**), gastrointestinal hemorrhage (**HP:0002239**), hemarthrosis (**HP:0005261**), muscle hemorrhage (**HP:0012233**, suggested), and intracranial hemorrhage (**HP:0002170**). Menorrhagia was reported in approximately **20% of homozygous women** in one review. Frequency estimates for other manifestations are unavailable because cohorts are extremely small. | Severe disease may present neonatally or in childhood; mild disease can first appear after dental extraction, surgery, trauma, menstruation, or childbirth. Clinical variability occurs even among individuals sharing a variant. (pqac-00000004, pqac-00000013) |
| Diagnostic signature | Both **PT and aPTT are typically prolonged**, reflecting a common-pathway defect; confirm using a one-stage factor II activity assay. Measure prothrombin antigen to distinguish type I from type II and use mixing studies to exclude an inhibitor. Evaluate vitamin-K status, liver disease, anticoagulant exposure, disseminated intravascular coagulation, and deficiencies of factors V, X, or fibrinogen. Confirm inherited disease with **F2 sequencing plus deletion/duplication analysis**; WES/WGS is useful when single-gene testing is negative or the phenotype is atypical. | Imaging is complication-directed, not diagnostic. CMA, karyotyping, FISH, mitochondrial testing, and repeat-expansion testing are ordinarily not indicated unless another syndrome is suspected. (pqac-00000003, pqac-00000004) |
| Treatment and hemostatic targets | For major bleeding or invasive procedures, use **prothrombin-complex concentrate (PCC) 20–30 IU/kg**, repeating according to factor level and clinical response. Suggested factor II target is **20–30%** for hemostasis and **30–40% for major surgery**. If PCC is unavailable, **fresh-frozen plasma 15–20 mL/kg** may be used, with fluid-overload risk. Antifibrinolytics and local hemostatic measures may supplement replacement for mucosal/dental bleeding. No specific purified factor II concentrate is generally available. | Suggested NCIt concepts: Prothrombin Complex Concentrate; Fresh Frozen Plasma Transfusion; Antifibrinolytic Therapy. PCC contains other vitamin-K-dependent factors and therefore carries thrombotic risk; management should be directed by a specialist bleeding-disorders center. (pqac-00000002) |
| Prognosis and temporal course | Lifelong, nonprogressive biochemical deficiency with episodic spontaneous or provoked bleeding. Prognosis is generally favorable when bleeding is recognized and replacement is available, but severe gastrointestinal, intracranial, neonatal, perioperative, or obstetric hemorrhage can be fatal or disabling. No robust survival rate, mortality rate, life-expectancy estimate, or disease-specific quality-of-life dataset is available. | Prognosis is influenced by residual factor II activity, functional variant effect, prior bleeding phenotype, treatment access, and exposure to trauma, surgery, pregnancy, or anticoagulants. (pqac-00000002, pqac-00000004) |
| Model organisms | **Mouse (Mus musculus; NCBI Taxon 10090):** F2 knockout causes embryonic hemorrhage, approximately **50% mortality by embryonic day 10.5**, and fatal postnatal hemorrhage in survivors. **Zebrafish (Danio rerio; Taxon 7955):** kringle-1-disrupting f2 mutation impairs secondary hemostasis; internal hemorrhage begins around one month and **23/24 homozygotes died by 90 days**. **Medaka (Oryzias latipes; Taxon 8090):** genome-edited thrombin-deficient mutants show markedly delayed coagulation. | Mouse models establish the survival requirement for prothrombin; fish models permit study of severe hypomorphic deficiency beyond embryogenesis. Zebrafish DOI [10.1038/s41598-020-60840-7](https://doi.org/10.1038/s41598-020-60840-7), March 2020. (pqac-00000005, pqac-00000007) |
| Evidence gaps and current research | There are no large natural-history cohorts, validated genotype-based prognostic models, disease-specific patient-reported outcome studies, approved gene/RNA/cell therapies, or confirmed disease-specific interventional trials in the gathered evidence. Recent work includes small sequencing studies—e.g., **12 southeastern Iranian patients** in 2023—and broader 2024 reviews emphasizing that management advances remain limited for rare bleeding disorders. Single-cell, spatial, transcriptomic, proteomic, metabolomic, lipidomic, and epigenomic disease signatures are unavailable or not established. | Iranian study: DOI [10.34172/cjmb.2023.10](https://doi.org/10.34172/cjmb.2023.10), February 2023. Absence of identified trials means “no trial found,” not proof that none exists. (pqac-00000014) |


*Table: Concise knowledge-base summary of congenital prothrombin deficiency, including genetics, phenotypes, diagnostics, treatment targets, models, ontology suggestions, and major evidence gaps.*