Diagnosis and treatment of inherited factor X deficiency

Summary. Factor X is a vitamin K‐dependent, liver‐produced serine protease that serves a pivotal role in coagulation as the first enzyme in the common pathway to fibrin formation. Inherited factor X deficiency is a rare autosomal recessive bleeding disorder that is estimated to occur in 1:1 000 000 individuals up to 1:500 carriers. Several international registries of FX‐deficient patients have greatly expanded the knowledge of clinical phenotype. A proposed classification of severity is based on FX:C activity measurements: an FX:C measurement <1% is severe, an FX:C measurement of 1–5% is moderate and an FX:C measurement of 6–10% is mild. Levels above 20% are infrequently associated with bleeding and heterozygotes are usually asymptomatic. Among patients with FX:C levels <10%, unlike moderate or severe haemophilia A and B, mucocutaneous bleeding symptoms such as epistaxis and menorrhagia occur in the majority. In addition, patients with moderate–severe deficiency may have symptoms similar to that of haemophilia A and B, including haemarthrosis, intracranial haemorrhage, and gastrointestinal bleeding. Genotype characterization may offer important clues about clinical prognosis. More than 80 mutations of the F10 gene have been identified, most of which are missense mutations. There is no specific FX replacement product yet readily available, but fresh frozen plasma and prothrombin complex concentrates can be used for treatment of bleeding symptoms and preparation for surgery.