Hemophilia B Leyden: Literature and Our Data

Hemophilia B is a monogenic X-linked recessive disorder associated with blood clotting reduction caused by mutations in the clotting factor IX gene (F9). An unusual form of this disorder, hemophilia B Leyden, caused by mutations in the promoter region of the F9 gene, is described. This form of hemophilia B is characterized by a significant, within norm, increase in factor IX in the patient’s plasma after puberty. Mutations in the promoter are grouped in discrete regions of transcription factor binding sites and alter the F9 gene expression during the ontogeny in different ways. This disorder demonstrates how single-nucleotide pathogenic variants in cis-regulatory regions can have a dramatic impact on gene expression. In this article, we present the current data on the F9 gene promoter structure and the results of examining three patients with hemophilia B Leyden who underwent genetic testing in the DNA-diagnostics laboratory of the Bochkov Research Centre for Medical Genetics.