Thalassemias

Thalassemias: The Basics - Globin Chain Game

• Quantitative defect: ↓ synthesis of one or more globin chains, leading to microcytic hypochromic anemia.
• Normal Adult Hb: HbA ($\alpha_2\beta_2$ >95%), HbA2 ($\alpha_2\delta_2$ 2-3.5%), HbF ($\alpha_2\gamma_2$ <1%).
• Types (gene locus):
  • α-Thalassemia: Defective α-chain synthesis (Chr 16, 4 α-genes).
  • β-Thalassemia: Defective β-chain synthesis (Chr 11, 2 β-genes).
• Pathophysiology: Globin chain imbalance → unpaired chains precipitate → RBC damage → ineffective erythropoiesis & hemolysis.

⭐ Hb Bart's ($\gamma_4$) is characteristic of severe α-thalassemia (hydrops fetalis).

Alpha Thalassemias - Alpha's Missing Acts

• Caused by deletions of α-globin genes (HBA1, HBA2) on chromosome 16. 📌 Alpha has 16 candles. Severity depends on number of deletions (1-4).
• Clinical Spectrum & Genotypes:

• Diagnosis: ↓MCV, ↓MCH, normal/↑RBC count. Peripheral smear: target cells, poikilocytosis. Hb electrophoresis (detects HbH, Hb Bart's). Genetic testing (DNA analysis) is confirmatory.

⭐ Hb Bart's (γ4) has an extremely high oxygen affinity, leading to severe tissue hypoxia and is the most severe form, causing hydrops fetalis.

Beta Thalassemias - Beta's Broken Beats

• Pathophysiology: Deficient $\beta$-globin chain synthesis (HBB gene, Chr 11). Excess $\alpha$-chains precipitate $\rightarrow$ ineffective erythropoiesis & hemolysis.
• Types:
  • Minor (Trait): Heterozygous ($\beta/\beta^+$ or $\beta/\beta^0$). Mild microcytic anemia. Key: $\uparrow$HbA2 (>3.5%).
  • Intermedia: Moderate severity; transfusion needs vary.
  • Major (Cooley's Anemia): Homozygous ($\beta^0/\beta^0$). Severe anemia (Hb <7 g/dL), massive hepatosplenomegaly, "hair-on-end" skull X-ray. Requires lifelong transfusions & iron chelation.
• Diagnosis: Hb electrophoresis (Major: $\uparrow\uparrow$HbF, $\uparrow$HbA2, $\downarrow\downarrow$/absent HbA). 

⭐ In Beta Thalassemia Major, HbF is markedly elevated, often >90%, as a compensatory mechanism for absent HbA production after birth.

Diagnosis & DDx - Spotting the Suspects

• Suspicion: Microcytic (MCV <80 fL), hypochromic anemia.
• Key Labs:
  • CBC: ↓Hb, ↓MCV, ↓MCH. RDW normal/↑.
  • Peripheral Smear (PS): Target cells, basophilic stippling, anisopoikilocytosis.
  • Reticulocyte count: Normal or ↑ (ineffective erythropoiesis).
• Confirmatory: Hb Electrophoresis / HPLC.
  • β-Thal Major: ↑↑HbF (often >90%), HbA absent/markedly ↓.
  • β-Thal Trait: ↑HbA2 (>3.5% - 7%).
  • α-Thal (HbH disease): HbH (β4) bodies detected.
• DDx (Microcytic Anemias): Iron Deficiency Anemia (IDA; ↓Ferritin, ↑TIBC), Anemia of Chronic Disease (ACD), Sideroblastic anemia, Lead poisoning.
• 📌 Mentzer Index: $MCV/RBC < \textbf{13}$ suggests Thalassemia trait.

⭐ In β-thalassemia trait, HbA2 levels are characteristically elevated, typically between 3.5% and 7%.

Management & Complications - Taming the Trouble

• Core Management: Lifelong transfusions, meticulous iron chelation. HSCT offers cure.
• Transfusion Goal: Pre-transfusion Hb 9-10.5 g/dL (leukoreduced PRBCs).
• Chelation Details: Start if ferritin >1000 ng/mL or 10-20 transfusions. Key agents: Deferoxamine, Deferasirox, Deferiprone.
• Iron Overload Complications: Cardiac (failure, arrhythmias - main death cause), endocrine (hypogonadism, DM), hepatic (fibrosis).
• Other Key Complications: Skeletal ("chipmunk facies"), gallstones, infections (Yersinia with deferoxamine).

⭐ Cardiac siderosis is the primary cause of mortality in transfusion-dependent thalassemia.

High‑Yield Points - ⚡ Biggest Takeaways

• α-Thalassemia: Caused by gene deletions. Hb Bart's (γ4) leads to hydrops fetalis; HbH disease (β4) causes chronic hemolytic anemia.
• β-Thalassemia: Results from point mutations. β-Thalassemia Major (Cooley's Anemia) is severe and transfusion-dependent; β-Thalassemia Minor shows characteristic ↑HbA2.
• Pathophysiology: Imbalanced globin chain synthesis leads to ineffective erythropoiesis, hemolysis, and subsequent iron overload.
• Clinical features: Severe microcytic hypochromic anemia, hepatosplenomegaly, and characteristic skeletal deformities (e.g., "crew-cut" skull X-ray).
• Diagnosis: Primarily by HPLC or Hb electrophoresis (↑HbF in β-Major, ↑HbA2 in β-Minor). Peripheral smear shows target cells.
• Management: Regular blood transfusions and iron chelation therapy are the mainstays of treatment for severe forms.