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HEMOPHILIA — High-Yield NEET PG Pathology Summary

Format: Structured for rapid revision. Mnemonics are in bold brackets [ ]. High-yield exam pearls are marked ⭐.

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1. OVERVIEW & CLASSIFICATION

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2. GENETICS & MOLECULAR BASIS

Hemophilia A — Factor VIII Gene Mutations

• Gene located on X chromosome (Xq28)
• Most common severe mutation: Intron 22 inversion → completely abolishes Factor VIII synthesis → Severe disease ⭐
• Point mutations → functional impairment (Factor VIII levels may be normal by immunoassay but functionally absent) ⭐
• Mutations allowing some active FVIII → Mild to moderate disease
• ~30% of cases have NO family history — due to new (de novo) mutations ⭐
• Rare occurrence in females: Unfavorable lyonization (X chromosome inactivation preferentially affects the normal allele) OR Turner syndrome (XO) or daughter of affected male + carrier female ⭐

Hemophilia B — Factor IX Gene Mutations

• Wide spectrum of mutations in FIX gene
• ~15% of patients: Factor IX protein present but nonfunctional (CRM+, cross-reacting material positive) ⭐
• 30–40% of carriers missed by FIX activity measurement alone → mutation analysis required for carrier detection ⭐
• ~1/3 of cases arise from spontaneous mutations (no family history)

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3. PATHOPHYSIOLOGY — WHY DO HEMOPHILIACS BLEED?

INTRINSIC PATHWAY (Contact activation):
XII → XI → IX → X → Prothrombin → Thrombin → Fibrin
                ↑
         Factor VIII (cofactor)
              (VIII + IXa = Xase complex → activates Factor X)

• Factor VIIIa + Factor IXa = Tenase complex → activates Factor X ⭐
• Without this complex → Factor X activation is severely impaired
• Tissue factor pathway (extrinsic) can initiate clotting but is quickly inhibited by TFPI
• The intrinsic tenase complex is critical for sustained, adequate thrombin generation — without it, initial hemostasis may occur but the clot is fragile and bleeding recurs

• Petechiae and mucocutaneous bleeding → platelet disorders
• Deep tissue/joint/muscle/CNS bleeding → coagulation factor disorders ⭐
• Iron from repeated hemarthroses → synovial uptake → release of IL-1β and IL-6 → chondrocyte apoptosis → cartilage damage ⭐

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4. SEVERITY CLASSIFICATION ⭐

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5. CLINICAL FEATURES

Cardinal Features (Coagulation-type bleeding):

• Hemarthroses (joint bleeding) — most characteristic ⭐
  • Target joints: Ankles > Knees > Elbows (hinge joints primarily) ⭐
  • Recurrent hemarthroses → restricted range of motion, muscle atrophy, arthropathy ⭐
• Deep muscle hematomas (iliopsoas hematoma can mimic appendicitis)
• Massive hemorrhage after trauma or surgery (disproportionate to injury)
• Spontaneous hemorrhage in severe disease
• Life-threatening: CNS hemorrhage, paratracheal hemorrhage ⭐

Characteristically ABSENT:

• Petechiae — absent in hemophilia (petechiae = platelet disorder) ⭐
• Prolonged bleeding from small cuts (primary hemostasis is intact)

Classic Presentations:

• Cephalohematoma at birth ⭐
• Prolonged bleeding after circumcision (described in the Talmud!) ⭐
• Post-IM injection hematoma (e.g., Vitamin K injection)
• Gum/dental bleeding with deciduous teeth loss

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6. LABORATORY DIAGNOSIS ⭐

Diagnostic Workup Sequence:

1. Isolated prolonged aPTT → suspect intrinsic pathway defect
2. Mixing study with normal pooled plasma:
   • Corrects → factor deficiency (hemophilia)
   • Does NOT correct → inhibitor/antibody present ⭐
3. Specific Factor VIII or IX activity assays for definitive diagnosis

Minimum Hemostatic Levels:

• Factor VIII: 30% of normal (plasma half-life: 8–12 hours)
• Factor IX: 30% of normal (plasma half-life: 18–24 hours — longer than FVIII) ⭐

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7. HEMOPHILIA A vs. B vs. vWD — DIFFERENTIATING TABLE ⭐

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8. COMPLICATIONS

1. Hemophilic Arthropathy ⭐

• Repeated hemarthroses → chronic synovitis → cartilage destruction
• Iron deposition in synovium → IL-1β, IL-6 release → chondrocyte apoptosis

2. Inhibitor (Alloantibody) Formation — Most Serious Complication ⭐

• Hemophilia A: ~15% (Robbins) to 29–45% (Henry's) of severe patients develop anti-FVIII inhibitors
• Hemophilia B: 1–3% develop anti-FIX inhibitors (especially with large FIX gene deletions) ⭐
• These are neutralizing alloantibodies that destroy exogenously administered factor
• Treatment with bypassing agents when inhibitors present:
  • Recombinant Factor VIIa (rFVIIa) — activates extrinsic pathway, bypasses VIII/IX ⭐
  • Anti-inhibitor Coagulant Complex (AICC / FEIBA) — activated prothrombin complex concentrate ⭐

3. Transfusion-Transmitted Infections (Historical)

• Pre-recombinant era: HIV and Hepatitis C transmission via plasma-derived concentrates
• Modern recombinant products: no blood-borne pathogen transmission documented ⭐

4. CNS Hemorrhage

• Most life-threatening complication
• Usually trauma-related

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9. TREATMENT ⭐

Hemophilia A — Factor VIII Replacement

Hemophilia B — Factor IX Replacement

Novel/Non-Replacement Therapies ⭐

• Bispecific antibody that bypasses the need for Factor VIII entirely
• Effective even in patients with inhibitors to Factor VIII
• Subcutaneous; given weekly/biweekly/monthly
• Does NOT replace Factor VIII — acts as a functional substitute

Prophylaxis vs. On-Demand:

• Primary prophylaxis: Starting factor replacement before first joint bleed (in severe disease) — prevents arthropathy ⭐
• Secondary prophylaxis: After first joint bleed to prevent recurrent bleeds
• On-demand: Treatment only at bleeding episodes (leads to more joint damage)

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10. PRENATAL DIAGNOSIS & CARRIER DETECTION

• Chorionic Villous Sampling (CVS) at 9–14 weeks ⭐
• Amniocentesis after 16 weeks
• Fetoscopic blood sampling at 20 weeks (highest risk, least preferred)
• Cell-free fetal DNA in maternal plasma — detectable within 10 days of conception ⭐
• For Hemophilia B: FIX activity alone misses 30–40% of carriers → mutation analysis mandatory ⭐
• Intron 22 inversion analysis for Hemophilia A carrier detection

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11. HEMOPHILIA C (Factor XI Deficiency) — Bonus

• Autosomal Recessive (NOT X-linked) ⭐
• Affects males AND females
• Common in Ashkenazi Jewish population
• Mild-moderate bleeding; hemarthroses rare
• aPTT prolonged, PT normal
• Treatment: FFP

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12. ACQUIRED HEMOPHILIA ⭐

• Autoantibodies against Factor VIII in patients without genetic deficiency
• Causes: Postpartum, autoimmune disease (SLE), malignancy, idiopathic
• Unlike congenital hemophilia: Joint bleeding less common; soft tissue and mucocutaneous bleeding more common
• Mixing study: Does NOT correct ⭐
• Treatment: Bypassing agents (rFVIIa, FEIBA) + immunosuppression to eradicate inhibitor

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13. HIGH-YIELD MNEMONICS & MEMORY AIDS

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14. QUICK REVISION CHECKLIST — NEET PG HOT TOPICS

• Most common hereditary life-threatening bleeding disorder = Hemophilia A
• Factor VIII gene = X chromosome; Intron 22 inversion = severe disease
• Hemophilia A & B both: X-linked recessive, intrinsic pathway, prolonged aPTT
• Christmas disease = Hemophilia B = Factor IX deficiency
• Hemarthroses — characteristic; Petechiae — absent
• Lab: ↑aPTT, Normal PT, Normal BT, Normal platelets
• Mixing study corrects = factor deficiency; doesn't correct = inhibitor
• Severity: <1% severe, 1–5% moderate, 6–30% mild
• Desmopressin: mild hemophilia A only
• Emicizumab: bispecific Ab, bypasses FVIII, works with inhibitors
• Inhibitor formation: most serious complication of FVIII replacement
• rFVIIa / FEIBA: bypassing agents for inhibitor patients
• Gene therapy: FDA approved for Hemophilia B
• vWD vs Hemophilia A: vWD has prolonged bleeding time, ristocetin abnormal, affects both sexes
• Acquired hemophilia: autoantibodies to FVIII, mixing study doesn't correct, postpartum/autoimmune
• Prenatal: CVS at 9–14 wk; fetal DNA in maternal plasma detectable at 10 days
• Hemophilia B carrier detection: FIX activity misses 30–40% → need mutation analysis

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