Hemophilia B: Symptoms, Signs, and Causes

Causes of Hemophilia B. Hemophilia B is caused by mutations in the F9 gene, which is responsible for producing clotting factor IX. This gene is located on the X chromosome, making Hemophilia B an X-linked recessive disorder. Since males have only one X chromosome, a single defective copy of the gene can result in the disease. Females have two X chromosomes, so a mutation would have to be present in both copies of the gene to exhibit the disorder, which is extremely rare. Most females who inherit a single defective gene are carriers and may pass the gene to their offspring.