A less severe form of Haemophilia B Leyden

Haemophilia B is an inherited, X-linked coagulation disorder, caused by mutations in the gene for clotting factor IX. The condition is heterogeneous and many of the causative mutations have been identified. The clinical severity of the disorder depends on the nature of the mutation. One rare form of haemophilia B, first identified in a Dutch family, and referred to as Haemophilia B Leyden is characterized by severe haemophilia in childhood progressing to a mild or an asymptomatic condition after puberty. Accordingly these patients are found to have low or undetectable concentrations of factor IX in plasma before puberty (typically