Haemophilia B

Related Subjects: |Haemophilia A |Haemophilia B |Haemolytic anaemia

An X-linked recessive bleeding disorder caused by Factor IX deficiency.

📖 About

• Also known as Christmas disease, named after the first reported patient 🎄.
• Bleeding disorder in males 👨 due to Factor IX deficiency.
• Prevalence: ~1 in 30,000 males 👦.

🧬 Aetiology

• Inherited Factor IX deficiency due to mutations in the FIX gene on the X chromosome.
• Males affected; females are carriers (except in Turner syndrome XO).

📊 Severity (by Factor IX Levels)

• Severe: <2% → spontaneous haemarthroses 🤕, muscle haematomas.
• Moderate: 2–10% → bleeding after minor trauma/surgery 🩸.
• Mild: 10–50% → excessive bleeding only after major surgery/trauma 🏥.

⚡ Clinical Features

• Bleeding usually not seen in early infancy 👶.
• Manifests with mobility/trauma in childhood 🚶.
• May present with excessive bleeding after circumcision ✂️.
• Muscle haematomas appear after ~6 months.
• Recurrent joint bleeds → chronic arthritis 🦵.
• Risk of intracranial haemorrhage, esp. post-trauma 🧠.
• Minor cuts/abrasions not problematic (platelets normal ✅).

🔬 Investigations

• APTT: prolonged ⏱️.
• Factor IX:C levels: low 📉.
• PT, bleeding time, platelet count: normal ✅.
• von Willebrand factor: normal (distinguishes from vWD).

🩺 Management

• Avoid NSAIDs, aspirin, and intramuscular injections 🚫.
• Factor IX replacement therapy is mainstay (plasma-derived or recombinant) 💉.
• Prophylaxis: Factor IX infusions, usually twice weekly for severe disease 🔄.
• Recombinant Factor IX safer than plasma-derived concentrates (no viral risk 🛡️).
• Desmopressin is ineffective 🚫 (does not affect Factor IX).

⚠️ Complications

• Historical: HIV and hepatitis C from contaminated blood products in 1970s–80s 🦠.
• Development of inhibitors (antibodies) against Factor IX may occur, complicating therapy ❌.

Cases - Haemophilia B

• Case 1 - Child with Severe Haemarthrosis: A 9-year-old boy presents with painful swelling of the left elbow after bumping into a desk at school. He has a history of recurrent joint bleeds since age 3. Coagulation profile: PT normal, APTT prolonged. Factor IX activity <1%. Diagnosis: Severe Haemophilia B with haemarthrosis.
• Case 2 - Adolescent with Surgical Bleeding: A 15-year-old boy develops uncontrolled bleeding following tonsillectomy. FBC is normal, PT normal, APTT prolonged. Factor IX level 4%. Diagnosis: Moderate Haemophilia B presenting with post-surgical haemorrhage.
• Case 3 - Adult with Inhibitors: A 28-year-old man with known severe Haemophilia B presents with a large thigh haematoma after football. Despite repeated Factor IX infusions, bleeding continues. Bethesda assay confirms inhibitor antibodies. Diagnosis: Haemophilia B complicated by inhibitors.

Teaching Commentary 🩸

Haemophilia B is an X-linked recessive deficiency of Factor IX, clinically indistinguishable from Haemophilia A. Severity is defined by Factor IX activity (<1% severe, 1–5% moderate, >5% mild). Typical presentations are spontaneous joint/muscle bleeds, prolonged bleeding after surgery, and delayed haemorrhage. Lab pattern: isolated prolonged APTT, with normal PT and platelets. Treatment is recombinant Factor IX replacement; mild cases may benefit from prophylaxis. Inhibitor development is less common than in Haemophilia A, but if present, management requires bypassing agents (e.g., recombinant Factor VIIa) or newer therapies like emicizumab (though licensed for Haemophilia A, it’s under investigation for B).