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Thalassemia: From Basic to Clinical

1. What Is Thalassemia?

Thalassemia is a group of inherited hemoglobin disorders caused by germline mutations that reduce or abolish the synthesis of either alpha (α) or beta (β) globin chains. The word comes from Greek - thalassa means "sea," reflecting its high prevalence around the Mediterranean basin.

Normal adult hemoglobin (HbA) is a tetramer made of 2 α-chains + 2 β-chains. When one chain is deficient, two problems occur simultaneously:

Not enough hemoglobin is made (hypochromic, microcytic red cells)
The other chain builds up in excess, precipitates, and damages red cell membranes - causing hemolysis

Robbins, Cotran & Kumar Pathologic Basis of Disease

2. Genetics - Where the Mutations Are

Chain	Gene Location	Mutation Type
α-globin	Chromosome 16 (2 genes per chromosome = 4 total)	Mainly gene deletions
β-globin	Chromosome 11 (1 gene per chromosome = 2 total)	Mainly point mutations (>100 types)

β-Thalassemia Mutations (3 classes):

Splicing mutations - most common cause of β+ (reduced output)
Promoter region mutations - reduce transcription by 75-80%
Chain terminator mutations - most common cause of β0 (zero output); nonsense or frameshift mutations

Two key mutation categories:

β0 = no β-globin produced at all
β+ = reduced but detectable β-globin produced
Robbins & Kumar Basic Pathology

3. Pathophysiology

The chain imbalance is the root of all the pathology:

Excess unpaired α-chains
       ↓
Precipitate inside RBC precursors
       ↓
Membrane damage → Intravascular + extravascular hemolysis
       ↓
Massive ineffective erythropoiesis in bone marrow
       ↓
Bone marrow expansion → skeletal deformities
       ↓
Compensatory extramedullary hematopoiesis → hepatosplenomegaly
       ↓
Increased GI iron absorption + transfusion iron → Iron overload

In α-thalassemia, excess β-chains form HbH (β4 tetramers), which has extremely high oxygen affinity and delivers little O2 to tissues. In the fetus, excess γ-chains form Hemoglobin Bart (γ4) with the same problem.

Robbins, Cotran & Kumar; Goldman-Cecil Medicine

4. Classification & Syndromes

β-Thalassemia Spectrum

β-Thalassemia severity spectrum showing minor (heterozygous, asymptomatic) to intermedia to major (homozygous, transfusion-dependent)

Form	Genotype	Hb Level	Key Feature
β-Thalassemia Minor (trait)	Heterozygous (1 abnormal allele)	Mildly low or normal	Asymptomatic carrier
β-Thalassemia Intermedia	Variable compound heterozygous	7-10 g/dL	Moderate anemia, no regular transfusions needed
β-Thalassemia Major (Cooley's anemia)	Homozygous (both alleles abnormal)	< 7 g/dL	Severe, transfusion-dependent, presents < 2 years

α-Thalassemia Spectrum (4 gene deletions possible)

Genes Deleted	Syndrome	Clinical Picture
1 (-/αα)	Silent carrier	Completely asymptomatic, slight microcytosis
2 (--/αα or -α/-α)	α-Thalassemia trait	Resembles β-thal minor - microcytosis, minimal anemia
3 (--/-α)	HbH disease	Moderate-severe hemolytic anemia, Hb ~7-9 g/dL
4 (--/--)	Hydrops fetalis (α-thal major)	Fatal in utero without intervention

Robbins, Cotran & Kumar

5. Clinical Symptoms That Confirm Thalassemia

Thalassemia Minor/Trait

Usually asymptomatic - discovered incidentally on CBC
Mild microcytosis (low MCV) with normal or near-normal hemoglobin
HbA2 > 3.5% on HPLC is the hallmark of β-thalassemia trait

Thalassemia Intermedia

Chronic fatigue, pallor, mild jaundice
Moderate splenomegaly
Presents in late childhood (after age 2)
Growth can be mildly retarded

Thalassemia Major (Cooley's Anemia) - Classic Presentation

Children present in the first 1-2 years of life with:

Anemia-related:

Severe pallor, profound fatigue, poor feeding
Growth retardation and failure to thrive
Hemoglobin < 7 g/dL

Expansion of erythroid marrow (bony changes):

"Crew cut" skull on X-ray (from marrow expansion)
"Chipmunk facies" - maxillary overgrowth, prominent forehead, frontal bossing
Pathological fractures

Hepatosplenomegaly:

Massive splenomegaly (from extramedullary hematopoiesis and red cell trapping)
Abdominal distension

Jaundice - from chronic hemolysis

Iron overload signs (in transfused/older patients):

Skin bronzing (hemosiderin deposition)
Cardiac failure (most common cause of death in poorly managed patients)
Endocrine: hypogonadism, delayed puberty, diabetes mellitus, hypothyroidism
Liver: progressive fibrosis and cirrhosis

HbH disease:

Jaundice, splenomegaly, hypochromic microcytic anemia
"Golf ball" inclusions in RBCs with brilliant cresyl blue stain
Goldman-Cecil Medicine; Robbins Pathology

6. Diagnosis

Test	Finding
CBC	Low MCV (< 70 fL), low MCH, microcytic hypochromic anemia
Peripheral smear	Target cells, tear-drop cells, basophilic stippling, nucleated RBCs
Hemoglobin electrophoresis / HPLC	↑ HbA2 (> 3.5%) in β-thal trait; ↑ HbF; absent/reduced HbA in major
Serum ferritin + iron studies	Normal/elevated (distinguishes from iron deficiency)
Genetic testing	Confirms specific mutations
Prenatal	Chorionic villus sampling or amniocentesis in at-risk couples

7. Treatment & Management

Thalassemia Minor

No specific treatment needed
Genetic counseling (important to identify at-risk couples)
Folic acid supplementation during pregnancy
Iron only if true co-existing iron deficiency is confirmed

HbH Disease

Folic acid 2-5 mg/day (especially in children)
Blood transfusions during hemolytic crises (infections can precipitate them)
Avoid oxidant drugs (e.g., primaquine, dapsone)

Thalassemia Major - Comprehensive Management

1. Regular Transfusion Therapy

Every 2-5 weeks to maintain pre-transfusion Hb > 9-10.5 g/dL
Use leukoreduced packed red cells to minimize reactions and pathogen transmission
Maintains growth, prevents bone deformities

2. Iron Chelation Therapy (mandatory with transfusions)

Deferoxamine (DFO) - subcutaneous infusion, 8-12 hrs/day, 5-7 days/week
Deferasirox - oral, once daily; preferred for convenience
Deferiprone - oral; has added benefit of cardiac iron removal
Monitoring: serum ferritin, MRI liver and cardiac iron

3. Splenectomy

Considered when hypersplenism causes excessive transfusion needs
Optimal management can delay or avoid the need
Post-splenectomy: penicillin prophylaxis + vaccinations (pneumococcal, meningococcal, Hib)

4. Hematopoietic Stem Cell Transplantation (HSCT)

The only proven curative option
Best outcomes in young, well-chelated patients with matched sibling donor
Also curative for α-thalassemia major (hydrops fetalis survivors on intrauterine transfusion)

5. Folic Acid

Supplementation for all forms with significant hemolysis

6. Emerging Therapies

Gene therapy - shows promise; luspatercept (targets ineffective erythropoiesis) is FDA-approved for transfusion-dependent β-thalassemia in adults
Regular endocrine, cardiac, and hepatic monitoring and treatment of iron overload complications
Goldman-Cecil Medicine, International Edition; Creasy & Resnik's Maternal-Fetal Medicine

8. Epidemiology & Why It Persists

Thalassemia is most common in the Mediterranean basin, Middle East, tropical Africa, Indian subcontinent, and Southeast Asia - precisely the malaria belt. Heterozygous carriers have a selective survival advantage against P. falciparum malaria, which explains why these mutations have remained so common in the population despite their harmful effects in homozygotes. - Robbins, Cotran & Kumar

Quick Summary Table

Feature	Minor	Intermedia	Major
Anemia	Mild/none	Moderate (7-10 g/dL)	Severe (< 7 g/dL)
Transfusions	Not needed	Occasional	Lifelong (every 2-5 weeks)
Iron chelation	Rarely	Sometimes	Always
Bony changes	No	Mild	Severe (chipmunk facies, crew-cut skull)
Hepatosplenomegaly	No	Moderate	Severe
Curative option	N/A	HSCT if severe	HSCT

Sources: Robbins, Cotran & Kumar - Pathologic Basis of Disease; Robbins & Kumar Basic Pathology; Goldman-Cecil Medicine International Edition; Creasy & Resnik's Maternal-Fetal Medicine.

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