✅ Model Answer:
• Diagnosis: Severe hemophilia A (factor VIII deficiency) – X-linked bleeding disorder. Prolonged PTT, normal PT and platelet count; factor IX normal, so factor VIII is the likely missing factor.
• Any other test: Factor VIII assay, Factor VIII inhibitor (Bethesda assay) to rule out inhibitor; genetic testing (F8 gene, intron 22 inversion) for carrier detection and prenatal diagnosis.
• What to do next: Factor VIII replacement (recombinant or plasma-derived) 25-40 IU/kg IV for acute bleeding. Consider starting prophylaxis (25-40 IU/kg 3x/week) to prevent hemarthrosis and joint damage.
• Follow-up plan: Monitor factor VIII trough levels, joint function, and inhibitor development (Bethesda assay every 3-6 months). Physical therapy for joint health. Avoid NSAIDs. Family counseling and genetic testing for carrier status.

✅ Model Answer:
• Gene: F8 gene located on the X chromosome (Xq28).
• Inheritance: X-linked recessive. Males are affected; females are carriers (can have mild symptoms due to skewed X-inactivation).
• Mutations: More than 3,000 mutations identified. Common mutation: intron 22 inversion (accounts for ~45% of severe cases).
• Protein: Factor VIII is a cofactor in the intrinsic coagulation pathway.
• Carrier testing: Genetic testing for female relatives, prenatal diagnosis via chorionic villus sampling or amniocentesis.

✅ Model Answer:
• Bleeding manifestations:
- Hemarthrosis: Bleeding into joints (knees, elbows, ankles) – most common, leads to chronic arthropathy.
- Muscle hematomas: Deep muscle bleeding.
- Easy bruising: Spontaneous or after minor trauma.
- Prolonged bleeding: After circumcision, dental procedures, or surgery.
- Intracranial hemorrhage: Life-threatening, especially in infancy.
- Hematuria: Blood in urine.
• Severity: Based on factor VIII level: severe <1%, moderate 1-5%, mild 5-40%.
• Physical exam: Joint swelling, decreased range of motion, muscle atrophy, soft tissue hematomas.

✅ Model Answer:
• Initial screening:
- PT – normal.
- PTT – prolonged (intrinsic pathway defect).
- Platelet count – normal.
• Confirmatory tests:
- Factor VIII assay: Low (<1% severe, 1-5% moderate, 5-40% mild).
- Factor IX assay: Normal (to differentiate from hemophilia B).
- Bethesda assay: To detect factor VIII inhibitors (if poor response to treatment).
- Genetic testing: F8 gene mutation analysis for carrier detection and prenatal diagnosis.
- vWF antigen and activity: To rule out von Willebrand disease.

✅ Model Answer:
• Factor VIII replacement:
- Recombinant FVIII: Preferred (reduced risk of viral transmission).
- Plasma-derived FVIII: Used in some settings.
- Dose: 25-40 IU/kg IV for mild-moderate bleeding; 50 IU/kg for severe bleeding or surgery.
- Prophylaxis: 25-40 IU/kg 3x/week to prevent hemarthrosis and joint damage (standard of care for severe hemophilia).
• Desmopressin (DDAVP): For mild hemophilia A (releases endogenous factor VIII).
• Antifibrinolytics: Tranexamic acid for mucosal bleeding (e.g., epistaxis).
• Avoid: NSAIDs, aspirin, intramuscular injections.
• Gene therapy: Emerging treatment option (valoctocogene roxaparvovec).

✅ Model Answer:
• Inhibitor development: Development of antibodies against factor VIII (Bethesda assay positive). Occurs in 20-30% of severe hemophilia A. Treatment: bypassing agents (rFVIIa, aPCC), immune tolerance induction (ITI).
• Chronic arthropathy: Progressive joint damage due to recurrent hemarthrosis (target joints: knees, elbows, ankles).
• Intracranial hemorrhage: Life-threatening, especially in infants.
• Muscle atrophy: Due to recurrent muscle bleeds.
• Transfusion-transmitted infections: Hepatitis B, C, HIV (less common with recombinant products).
• Pseudotumor: Cystic masses in bones or muscles due to chronic bleeding.

✅ Model Answer:
• Prognosis:
- Excellent with early diagnosis and modern treatment (prophylaxis).
- Life expectancy: Near-normal with prophylaxis and inhibitor management.
- Morbidity: Mainly due to joint arthropathy and inhibitor development.
- Mortality: Rare (usually from intracranial hemorrhage or HIV/hepatitis in developing countries).
• Long-term follow-up:
- Joint health: Regular physiotherapy, monitoring for target joints.
- Inhibitor surveillance: Bethesda assay every 3-6 months.
- Prophylaxis: Lifelong factor VIII replacement (or gene therapy in the future).
- Education: Recognize early signs of bleeding, avoid aspirin/NSAIDs, and emergency management.
- Genetic counseling: For family members and prenatal diagnosis.

✅ Model Answer:
• Definition: Regular factor VIII replacement to prevent bleeding episodes and joint damage.
• Indications: Severe hemophilia A (factor VIII <1%) – standard of care.
• Regimen:
- Primary prophylaxis: Starting at age 1-2 years, before the onset of joint disease.
- Dose: 25-40 IU/kg IV 3x/week (or every other day).
- Goal: Maintain factor VIII trough levels >1% to prevent spontaneous bleeding.
• Benefits:
- Prevents hemarthrosis and chronic arthropathy.
- Improves quality of life and joint function.
- Reduces hospitalizations and emergency visits.
• Monitoring: Factor VIII trough levels, joint exams, and inhibitor screening.
• Alternatives: Emicizumab (bispecific antibody) for patients with inhibitors.