Prothrombin thrombophilia results from a specific pathogenic variant — designated c.*97G>A per HGVS nomenclature (commonly called 20210G>A) — in the F2 gene on chromosome 11, which encodes coagulation factor II (prothrombin). ClinGen has classified this gene-disease association as DEFINITIVE. The variant leads to elevated plasma prothrombin concentrations, increasing the tendency for venous clot formation. Inheritance follows an autosomal dominant pattern; heterozygous individuals carry one copy of the variant on one F2 allele. Homozygosity for the variant, which occurs at a frequency of approximately 1 in 10,000 individuals, confers higher thrombotic risk than heterozygosity. The variant prevalence varies substantially by population: heterozygosity rates of 1.7–3% are observed in general US and European populations, with higher rates in southern Europe and lower rates in northern Europe. The variant is extremely rare in Asian, African, and Native American populations. GeneReviews notes that prothrombin thrombophilia as a result of a de novo pathogenic variant has not been reported; all identified individuals have inherited the variant from a parent.

According to GeneReviews, no clinical features are specific to prothrombin thrombophilia; the diagnosis is based on molecular genetic testing identifying the F2 20210G>A variant. GeneReviews identifies clinical scenarios in which testing warrants consideration: a first unprovoked VTE before age 50 years; recurrent VTE; venous thrombosis at unusual sites such as cerebral, mesenteric, portal, or hepatic veins; VTE during pregnancy or the puerperium; VTE associated with estrogen-containing oral contraceptives or hormone replacement therapy; or an unprovoked VTE in an individual with a first-degree family member with VTE before age 50. The diagnosis is established by targeted molecular analysis for the F2 20210G>A variant, which detects 100% of probands. Multigene panel testing including the F2 variant is an alternative approach noted in GeneReviews. GeneReviews notes that plasma prothrombin concentration measurement is not a reliable diagnostic tool because the range in heterozygotes overlaps with the normal range. GeneReviews also identifies clinical contexts for which F2 variant testing is not indicated: general population screening, routine pre-exposure testing before contraceptive or HRT initiation, adults with VTE from major transient risk factors, and routine testing in asymptomatic children.

Management of thrombosis in prothrombin thrombophilia, as described in GeneReviews, is based on the clinical circumstances of the thrombotic event. The primary therapeutic approach involves anticoagulation for treatment of acute VTE and for prevention of recurrence. GeneReviews describes both direct oral anticoagulants and vitamin K antagonists as anticoagulant approaches used in clinical practice; treatment selection reflects individual clinical circumstances, comorbidities, and patient factors. The duration of anticoagulation depends on whether the thrombotic event was provoked by a transient risk factor or unprovoked, as well as on individual assessment of recurrence and bleeding risk. GeneReviews notes that heterozygosity for the 20210G>A variant alone, in the absence of other risk factors, is not an indication for long-term anticoagulation per published guidelines. For children with VTE, treatment recommendations are largely adapted from adult data; choice of anticoagulant in children is individualized based on the clinical situation. FDA-approved treatment data are not certified in this packet.

GeneReviews identifies specific circumstances to avoid: women with a history of VTE and the 20210G>A variant, and women who are homozygous for the variant regardless of VTE history, are described in GeneReviews as having clinical considerations regarding estrogen-containing contraception and hormone replacement therapy due to the substantially increased thrombotic risk associated with these exposures.

The clinical course of prothrombin thrombophilia is variable. Many heterozygous and homozygous individuals never develop a thrombotic event. When VTE occurs, GeneReviews notes that conflicting data exist regarding the magnitude of recurrence risk attributable specifically to the F2 20210G>A variant; any increased risk of recurrence after a first treated VTE is described as small. In children, inherited thrombophilia appears to have at most a modest effect on recurrence risk, consistent with findings in adults. Prognosis depends on the clinical circumstances of thrombotic events, the effectiveness of anticoagulation, and the balance between recurrence risk and anticoagulation-related bleeding risk as individually assessed. Long-term anticoagulation is periodically reevaluated to confirm that benefits continue to outweigh bleeding risk.

The certified research landscape for prothrombin thrombophilia includes 219 classified publications. Reviews and meta-analyses represent the dominant research type, with 94 classified review publications — reflecting decades of clinical investigation. Case reports number 7 among classified publications. The literature also includes publications on gene therapy and biomarker topics, as well as publications related to clinical trials. Clinical trial data are not certified in this packet. No patient advocacy organizations are listed in this packet for this condition.