Does sickle cell trait reduce the frequency of spontaneous bleeds in severe haemophilia?

Haemophilia A is an X-linked recessive disorder associated with deficiency of coagulation factor VIII and lifelong bleeding diathesis. Sickle cell trait (SCT) is the heterozygous state for the sickle β-globin gene. The frequency of SCT is up to 30% in Africa, wherein it confers survival advantage by providing resistance against severe malaria. SCT does not cause vaso-occlusive crisis, but is associated with high risk of venous thromboembolism as variously reported in the literature. We consider SCT as a hypercoagulable prothrombotic state and hypothesise that coinheritance of SCT may ameliorate the clinical phenotype of severe haemophilia. We conducted a retrospective analysis of frequencies of spontaneous bleeding among severe haemophiliacs with SCT (Hb AS phenotype) and their counterparts with normal Hb phenotype (Hb AA phenotype) in order to determine the possible ameliorating effect of SCT on spontaneous bleeding rates in severe haemophilia A. If our hypothesis is correct, severe haemophiliacs with SCT will have lower frequencies of spontaneous bleeding than their counterparts with normal Hb phenotype. Our results revealed that severe haemophiliacs with normal Hb phenotype had significantly higher mean annual bleeding episodes per patient in comparison with their counterparts with SCT (45±7 vs 31±5, p=0.033), suggesting that severe haemophiliacs with SCT had lower frequencies of spontaneous bleeding episodes. The result of this study indicates that coinheritance of SCT in patients with severe haemophilia may be associated with reduced frequency of spontaneous bleeding, which may imply better overall prognosis. However, the study has important limitations, which include its retrospective nature and the very low number of subjects. The findings should therefore be validated by a larger and prospective study.