Prevalence of sporadic and familial haemophilia.

In an analysis of 804 haemophilia pedigrees, mild to moderate haemophilia A or B was found to be clearly familial in 70% of cases, severe haemophilia B in 57% of cases and severe haemophilia A in 45% of cases. The rest of the patients were 'sporadic' i.e., either isolated cases or brothers in the first affected sibship. In sporadic families, 88% of mothers but only 19% of maternal grandmothers had the relevant mutation in their white blood cells. Among patients with familial haemophilia, half the patients with mild haemophilia and those with severe haemophilia B had a direct male ancestor with haemophilia, but only 28% of patients with severe haemophilia A had such a progenitor.