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Factor II deficiency is the most rare coagulation factor deficiency. Prevalence of homozygous forms is estimated at 1/2,000,000. Both sexes are equally affected.

Congenital FII deficiency can manifest at any age, with severe forms of the disease manifesting early in life. Common clinical signs include epistaxis, menorrhagia, oral cavity bleedings, mucosal bleeding, soft tissue bleeding, hemarthrosis, easy bruising, and prolonged bleeding after tooth extraction, trauma or surgery. Severe forms may present intracranial hemorrhage. The severity of the bleeding manifestations correlates with the FII levels. Thromboembolic manifestations have been described in case of dysprothrombinemia.

Inherited FII deficiency is caused by mutations in the F2 gene (11p11-q12) encoding prothrombin.

Diagnosis is based on prolonged prothrombin and activated partial thromboplastin times (PT, aPTT) and on low FII coagulant activity measured using a PT based assay. Molecular testing is available, but is unnecessary for diagnosis.

Differential diagnoses include deficiencies of factors V, VII, X, VIII, IX, XI, XIII or acquired deficiencies in FII (lupus anticoagulant).

Prenatal diagnosis is available for the most severe forms.

Transmission is autosomal recessive. Genetic counseling should be offered to at-risk couples (both individuals are carriers of a disease-causing mutation) informing them of the 25% risk of having an affected child at each pregnancy.

Prothrombin Complex Concentrates (PCCs) or fresh frozen plasma (if PCCs are not available) are usually used to treat hemorrhagic episodes.

Prognosis is good with early diagnosis and adequate treatment.