Hemofilie B Leyden

– Haemophilia B Leyden is characterized by an increase of factor IX activity after puberty, owing to which the initially severe clinical symptoms gradually grow milder and ultimately disappear altogether. The results of an extensive genealogical study suggest that the disease in the Netherlands involves only a single family. The family tree is so extensive, however, that in every new case of haemophilia B the possibility of this unusual variant has to be taken into account, because it is important for the treatment and the prognosis. Outside the Netherlands, this variant so far has only been described in a Greek family.