Genomic newborn screening: ICoNS
Gene: F9
Reviewed at ICoNS Gene List Subcommittee.
Generally accepted as meeting threshold for inclusion. However, consideration should be given as to whether to only report variants associated with severe disease and also on whether to report in females or not.Created: 5 Dec 2025, 6:30 a.m. | Last Modified: 5 Dec 2025, 6:30 a.m.
Panel Version: 0.16
Well established gene-disease association.
Mechanism: hemizygous loss of function variants in males, but heterozygous females may present with mild clinical symptoms due to nonrandom X-inactivation.
Incidence: 1 per 25-30K males births with >40 % having severe disease.
Clinical disease types:
Severe hemophilia B: < 1% normal FIX level. Usually diagnosed during the first two years of life. Characterized by spontaneous bleedings if not treated.
Moderate hemophilia B: 1-5% normal FIX levels. Prolonged bleeding after trauma, diagnosed before the age of 5.
Mild hemophilia B: 5- 40% normal FIX levels. Typically, no spontaneous bleedings, not diagnosed until later in life.
Pathogenic variants:
>1300 pathogenic variants, mostly point mutations, but also partial and full gene deletions.
Medical management informing pathogenic variants
• Complete gene deletions or major rearrangements are associated with severe anaphylactic reactions upon FIX replacement therapy. High risk for developing FIX inhibitors (> 50 %).
• Point mutations in promoter region (5'UTR) associated with Hemophilia B Leyden, characterized by developmental expression of FIX post puberty. At childhood, FIX levels are <1%, and increase with growth reaching up to 70% of normal levels. Anabolic steroids can help raise FIX levels.
• Missense variants in the FIX propeptide sequence causing reduced affinity to vitamin-K dependent carboxylase. These individuals have normal levels of FIX, but develop unexpected reduction of FIX upon administration of vitamin K antagonists (e.g. warfarin)
Treatment:
• Factor replacement therapy: Prophylaxis and early treatment
• Non-factor therapies: available for patients >12 y of age.
• Adeno-associated virus gene therapy: for adult males with <2% of FIX levels
• Surveillance and Supportive care
PMIDs: 16643212, 25851415, 3286010, 3416069, 35269902
https://www.cdc.gov/hemophilia/mutation-project/index.htmlCreated: 4 Dec 2025, 10:53 a.m. | Last Modified: 5 Dec 2025, 6:26 a.m.
Panel Version: 0.16
Mode of inheritance
X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males)
Phenotypes
Hemophilia B
Publications
Variants in this GENE are reported as part of current diagnostic practice
Gene: f9 has been classified as Green List (High Evidence).
Phenotypes for gene: F9 were changed from Hemophilia B to Haemophilia B, MIM# 306900
Publications for gene: F9 were set to
Gene: f9 has been classified as Green List (High Evidence).
gene: F9 was added gene: F9 was added to Genomic newborn screening: ICoNS. Sources: Expert list Mode of inheritance for gene: F9 was set to X-LINKED: hemizygous mutation in males, monoallelic mutations in females may cause disease (may be less severe, later onset than males) Phenotypes for gene: F9 were set to Hemophilia B Penetrance for gene: F9 were set to Complete