Hemoglobinopathies

Hemoglobinopathies - Basics & Blood Bonds

• Hemoglobinopathies: Genetic disorders affecting hemoglobin (Hb) structure or synthesis.
  • Qualitative: Abnormal globin chain structure (e.g., Sickle Cell Disease).
  • Quantitative: Reduced synthesis of normal globin chains (e.g., Thalassemia).
• Normal Adult Hemoglobins:
  • HbA ($α_2β_2$): >95%
  • HbA2 ($α_2δ_2$): 1.5-3.5%
  • HbF ($α_2γ_2$): <1-2% (higher in infants)
• Inheritance: Most are Autosomal Recessive.

⭐ HbF is the predominant hemoglobin during fetal life, which gradually decreases after birth as HbA production increases.

Sickle Cell Syndromes - Crescent Calamity

• Autosomal recessive; β-globin gene mutation (GAG→GTG; Glu→Val at codon 6) → HbS.
• Pathophysiology: Deoxygenation → HbS polymerization → RBC sickling → microvascular occlusion, hemolysis.

• Clinical Features:
  • Vaso-occlusive crisis (VOC): Severe pain.
  • Acute Chest Syndrome (ACS): Fever, cough, chest pain, hypoxia.
  • Splenic sequestration (infants) → autosplenectomy (adults) → ↑ risk: encapsulated organisms (S. pneumo, H. flu, N. menin).
  • Aplastic crisis (Parvovirus B19).
  • Dactylitis (hand-foot syndrome; often 1st sign).
  • Stroke, priapism, avascular necrosis.
• Diagnosis:
  • Newborn screening.
  • Hb electrophoresis/HPLC: HbS predominant, ↑ HbF, no HbA (in HbSS).
  • Peripheral smear: Sickled cells, Howell-Jolly bodies.
• Management:
  • Hydroxyurea: ↑ HbF, ↓ VOCs.
  • Folic acid supplementation.
  • Vaccinations (Pneumococcal, etc.).
  • Pain control, hydration.
  • Transfusions.
  • Stem cell transplant (curative).

⭐ Howell-Jolly bodies on peripheral smear indicate splenic dysfunction/asplenia.

Thalassemias - Chain Chain Woes

Quantitative defect in globin chain synthesis (α or β). Results in microcytic hypochromic anemia.

• Alpha (α) Thalassemia: Due to gene deletions on chromosome 16 (αα/αα).

  • 1-2 deletions (-α/αα or -α/-α or --/αα): Silent carrier or α-thalassemia trait. Usually asymptomatic or mild microcytic anemia.
  • 3 deletions (--/-α): HbH disease. Excess β chains form HbH (β4). Chronic hemolytic anemia, jaundice, splenomegaly. Golf ball inclusions (Heinz bodies) with supravital stain.
  • 4 deletions (--/--): Hb Barts. Excess γ chains form Hb Barts (γ4). Severe intrauterine hypoxia, hydrops fetalis. Usually fatal.
  • Diagnosis: Genetic testing. Hb electrophoresis shows HbH or Hb Barts.

• Beta (β) Thalassemia: Due to point mutations in β-globin gene on chromosome 11.

  • β-Thalassemia Minor (Trait): Heterozygous (β/β⁰ or β/β⁺). Mild asymptomatic anemia. ↑HbA2 (>3.5%), sometimes ↑HbF.
  • β-Thalassemia Intermedia: Homozygous mild or compound heterozygous moderate mutations. Variable severity, may not require regular transfusions.
  • β-Thalassemia Major (Cooley's Anemia): Homozygous (β⁰/β⁰) or severe compound heterozygous (β⁰/β⁺). Severe transfusion-dependent anemia by 4-6 months. Massive hepatosplenomegaly, bone marrow expansion (frontal bossing, chipmunk facies, "crew-cut" on X-ray), iron overload.
  • Diagnosis: Hb electrophoresis (↓/absent HbA, ↑↑HbF, variable ↑HbA2).

• Management (Moderate/Severe):

  • Regular packed RBC transfusions (maintain Hb >9-10 g/dL).
  • Iron chelation therapy (e.g., Deferoxamine, Deferasirox, Deferiprone) to prevent iron overload complications.
  • Folic acid supplementation.
  • Splenectomy (if hypersplenism).
  • Allogeneic hematopoietic stem cell transplantation (HSCT) is curative.

⭐ Target cells (codocytes) are a characteristic, though not specific, finding on peripheral smear in thalassemias due to relative membrane redundancy.

Diagnostic Approach & Other Variants - Spotting the Suspects

• Screening: CBC (↓Hb, abnormal MCV/MCH), Retic count, Peripheral Smear (RBC morphology: target cells, sickled cells, crystals).
• Confirmation: HPLC (gold standard), Hb Electrophoresis. Genetic tests for unclear/atypical cases.
• Newborn Screening (NBS): Crucial for early detection (SCA, β-Thal Major), allows timely intervention.

• Key Variants:
  • HbC: Mild hemolysis, target cells, HbC crystals (rod-like).
  • HbE: SE Asia; mild microcytic anemia; HbE co-migrates with HbA2.
  • HbD-Punjab: Often asymptomatic; co-migrates with HbS (differentiate via solubility test - HbD is soluble).

⭐ On alkaline electrophoresis (pH 8.6), Hb migration: A > F > S/D/G > E/O/C (Anode to Cathode). 📌 Mnemonic: All Fine Sick Doctors Go East Or Centre.

High‑Yield Points - ⚡ Biggest Takeaways

• Sickle Cell Anemia (SCA): HbS (β-globin Glu→Val), autosomal recessive. Features vaso-occlusive crises; hydroxyurea ↑HbF.
• β-Thalassemia Major: Absent/reduced β-globin chains cause severe microcytic hypochromic anemia; transfusion-dependent with iron chelation.
• α-Thalassemia: α-globin gene deletions lead to Hb Bart's (hydrops fetalis) or HbH disease.
• Diagnosis: HPLC is gold standard. Newborn screening is key.
• SCA Complications: Aplastic crisis (Parvovirus B19), risk of sepsis (prophylaxis needed).
• HbE Trait/Disease: Common in NE India/SE Asia; often mild. HbE/β-thalassemia is severe_._