Hemophilia A & B

About this condition

Hemophilia A and B are X-linked recessive bleeding disorders caused by mutations in F8 (factor VIII) and F9 (factor IX) respectively. These genes encode essential coagulation factors that form the intrinsic tenase complex — a critical step in the coagulation cascade. Loss-of-function F8 or F9 variants impair thrombin generation and clotting efficiency, causing spontaneous and trauma-induced bleeding. Hemophilia A affects approximately 1 in 5,000 males; Hemophilia B affects approximately 1 in 30,000 males. Severity correlates with factor levels: severe (<1% activity), moderate (1–5%), and mild (>5–40%). Clinical manifestations include hemarthroses (joint bleeds), muscle hematomas, intracranial hemorrhage, and spontaneous bleeding in severe forms.

Approximately 50% of severe Hemophilia A cases are caused by a single recurrent mutation — an intron 22 inversion (Inv22) — which disrupts F8 structure through intrachromosomal recombination. Over 2,500 F8 variants and over 1,100 F9 variants have been identified. Carrier females may express mild bleeding symptoms due to skewed X-inactivation (lyonization). Approximately 30% of Hemophilia A patients develop inhibitor antibodies (alloimmunization) against factor VIII during treatment — a serious complication requiring specialized management with activated prothrombin complex concentrate (aPCC) or recombinant factor VIII with high-dose bypassing activity. Inhibitor development is particularly common in severe Hemophilia A patients with Inv22 mutations.

A confirmed F8 or F9 pathogenic variant enables appropriate factor replacement therapy — dramatically improving outcomes through recombinant or plasma-derived factor VIII or IX. Severity classification (severe, moderate, mild) based on factor levels and variant type informs management intensity. Prophylactic factor replacement prevents hemarthroses and enables normal activity. Extended half-life factor products now reduce infusion burden substantially. Severe hemophilia A patients with Inv22 mutations face particularly high inhibitor development risk — immune tolerance therapy (high-dose factor replacement) may prevent or overcome inhibitor formation. Genetic diagnosis enables identification of female carriers, who may have bleeding symptoms and require testing and counseling.

The F8 intron 22 inversion (Inv22) causes approximately 50% of severe Hemophilia A — a structural variant that requires specialized detection methods and predicts high inhibitor development risk.

Gene locus: F8 (Xq28), F9 (Xq27.1)

Standard hemophilia panels may miss large deletions and structural variants. The F8 intron 22 inversion requires specialized detection — standard short-read sequencing is insufficient.

The F8 intron 22 inversion requires specialized detection methods

Hemophilia detection relies on specialized F8/F9 testing. Large deletions (common in hemophilia) may not be detected by exome sequencing alone; multiplex ligation-dependent probe amplification (MLPA) is often required. The Inv22 inversion — responsible for approximately 50% of severe Hemophilia A cases — is caused by intrachromosomal recombination between introns 22 and 1 and cannot be detected reliably by standard short-read WGS. Detection of Inv22 requires long-range PCR, Southern blot, or long-read sequencing. Whole genome sequencing with long-read capacity and supplementary structural variant analysis can detect Inv22 and large deletions that standard approaches miss.

Genetic subtype predicts inhibitor risk and guides prophylaxis intensity

An F8 or F9 pathogenic variant diagnosis enables appropriate factor replacement therapy and risk stratification. Severe hemophilia A patients with Inv22 mutations face approximately 30–40% risk of inhibitor antibody development — alloimmunization that requires specialized bypassing therapy. Immune tolerance therapy (high-dose factor replacement) may prevent or overcome inhibitor formation, but identifying Inv22 mutations early is critical for preventive strategies. Genetic diagnosis enables identification of female carriers, who may have bleeding symptoms. Prophylactic factor replacement prevents hemarthroses and enables normal physical activity.

Bleeding that doesn't stop the way it should — a clotting factor your body can't produce enough of. Identifying the exact variant determines which therapy works and how your family carries the trait.

Hemophilia A & B

Standard hemophilia panels may miss large deletions and structural variants. The F8 intron 22 inversion requires specialized detection — standard short-read sequencing is insufficient.

The F8 intron 22 inversion requires specialized detection methods

Genetic subtype predicts inhibitor risk and guides prophylaxis intensity

One test. A lifetime of answers.

Bleeding that doesn't stop the way it should — a clotting factor your body can't produce enough of. Identifying the exact variant determines which therapy works and how your family carries the trait.

Hemophilia A & B

Standard hemophilia panels may miss large deletions and structural variants. The F8 intron 22 inversion requires specialized detection — standard short-read sequencing is insufficient.

The F8 intron 22 inversion requires specialized detection methods

Genetic subtype predicts inhibitor risk and guides prophylaxis intensity

Others in Rare Diseases

One test. A lifetime of answers.