What is the difference between hemophilia carriers and hemophilia?¶
Answer: Hemophilia experts, in consultation with patient advocacy groups, replaced the old "carrier vs. hemophilia" split with a five-category nomenclature keyed to factor level and bleeding phenotype.
The term "hemophilia carrier" (HC) understates bleeding symptoms in women/girls. A new HC nomenclature was defined by hemophilia experts consulting with patient advocacy groups.
Five new HC categories are: severe/moderate/mild hemophilia, symptomatic and asymptomatic HC.
By FVIII/FIX level:
- Severe hemophilia — <0.01 IU/mL
- Moderate hemophilia — 0.01–0.05 IU/mL
- Mild hemophilia — >0.05 and <0.40 IU/mL
- Level ≥0.40 IU/mL with a bleeding phenotype — symptomatic carrier
- Level ≥0.40 IU/mL without a bleeding phenotype — asymptomatic carrier
Genetics and bleeding: In most instances, as in men, hemophilia in women results from an inherited variant on a single X chromosome, though the relationship between mutation type and factor level in carriers is poorly understood. Rarely, a woman inherits an affected X chromosome from both parents, or has an extremely skewed X-inactivation pattern, producing moderate or severe hemophilia. About one in four carriers with normal factor levels (>0.50 IU/mL) still have an increased bleeding tendency — in hemophilia A carriers partly from an impaired FVIII response to hemostatic stress — typically manifesting as mucocutaneous bleeding; bleeding after dental work, surgery, or childbirth; and joint bleeds with consequent poor joint health and quality of life.
Related: 0013 — FVIII levels and bleeding in hemophilia A carriers — what determines whether a carrier bleeds.