Recovery from hemophilia B Leyden: an androgen-responsive element in the factor IX promoter.

One form of the inherited, X-linked, bleeding disorder, hemophilia B, resolves after puberty. Mutations at -20 and -26 in the clotting factor IX promoter impair transcription by disrupting the binding site for the liver-enriched transcription factor LF-A1/HNF4. The -26 but not the -20 mutation also disrupts an androgen-responsive element, which overlaps the LF-A1/HNF4 site. This explains the improvement seen in patients with the -20 mutation and the failure of the -26 patient to recover.