In most of these discrepant cases, the factor VIII levels are red

In most of these discrepant cases, the factor VIII levels are reduced by 50% or more when measured by a two-stage assay as compared with a one-stage assay and this can lead to missing the diagnosis of mild haemophilia A when a one-stage assay is used as a screening method. The reverse situation, higher factor VIII levels

with a two-stage method than with a one-stage method, is less frequent. Mutations and molecular mechanisms of many of these discrepant cases have been resolved [12–14]. However, it remains unclear which assay is the best reflection of the bleeding phenotype. Using thrombin generation assays in patients with the more common discrepancy pattern (FVIII lower by two-stage assay), the most significant correlation was found between the one-stage FVIII assay and thrombin generation [12]. In two families with the

‘reversed discrepancy’ (FVIII higher by two-stage assay) and contrasting clinical histories (one family bleeding and one non-bleeding), impaired thrombin generation reflected the bleeding phenotype [15]. Characterization of the molecular mechanisms resulting in low FVIII levels have helped to identify regions of the factor VIII gene critical for proper factor VIII biosynthesis, thrombin activation, intramolecular stability as well as binding regions for important partners such as von Willebrand factor, factor IXa and the phospholipid surface [16]. In patients with the common presentation of mild haemophilia A with reduced FVIII activity in a two-stage assay as compared with a one-stage assay, a number of missense mutations mainly clustered within the A domains have been described that lead to defective stability

of FVIIIa. Conversely, mutations impairing FVIII activation by thrombin result in higher FVIII activity in a two-stage than in a one-stage assay [14]. Some particular FVIII missense mutations, mainly located within the region encoding for the light chain of factor VIII, contribute to an unexpectedly high incidence of inhibitors in mild haemophilia A [16,17]. Genetic testing might thus become an important key feature in the management of mild haemophilia A patients. Most patients with mild haemophilia A respond well to the administration of desmopressin which typically results in a 2–6-fold increase of FVIII levels Selleckchem Forskolin over baseline [18]. The peak postdesmopressin levels of FVIII depend on the patient’s basal FVIII level [19] and postdesmopressin FVIII half-life, typically around 5–8 h, is positively related to basal and peak von Willebrand Factor Antigen levels and patient age [20]. Young children often have a markedly lower response to desmopressin than adults [21]. Postdesmopressin FVIII levels >0.30 IU mL−1 are considered clinically adequate at least for the treatment of spontaneous or posttraumatic bleeding, whereas a postdesmopressin FVIII level of at least 0.50 IU mL−1 is required for the treatment of major surgery.

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