Milder clinical presentation of haemophilia A with severe deficiency of factor VIII as measured by one-stage assay.

During the course of investigations we encountered 11 patients with haemophilia A who had severe factor VIII deficiency as measured by one-stage assay but had surprisingly mild clinical presentation. Four of these patients had either a brother, nephew or maternal uncle with severe clinical manifestations. Two patients had low protein S levels, and one was heterozygous for the factor V Leiden mutation. One patient had a combined deficiency of protein C and antithrombin III. Four patients had a two-stage factor VIII assay value that was much higher than the one-stage assay value. Five patients were heterozygous for the MTHFR gene C677T polymorphism, of whom two patients were also deficient for protein S and one had two-stage factor assay values higher than the one-stage assay values. The patient who was both factor VIII deficient and heterozygous for factor V Leiden had mild clinical presentation as compared to his maternal uncle who was only factor-VIII deficient. The maternal cousin of the same patient was heterozygous for factor V Leiden and had suffered two thrombotic episodes. Thus, the present study advocates that the physiological inhibitors of blood coagulation also play an important role in cases of haemophilia A in the final outcome of haemostasis in vivo.