Thalassemias — Alpha and Beta

Molecular Basis of Beta-Thalassemia

• Mutations in the β-globin gene (chromosome 11) lead to reduced (β+) or absent (β0) β-globin chain production
• Mutation types include point mutations in the coding sequence, splice sites, promoter regions, or polyadenylation signals, deletions, and insertions
• Loss of β-chain synthesis results in relative excess of α-globin chains, which precipitate as α-globin tetramers (β4 chains)
• These unstable tetramers form insoluble inclusions that damage the erythrocyte membrane, triggering hemolysis and ineffective erythropoiesis
• Severity correlates with the degree of β-globin reduction: β0 (no production) = thalassemia major; β+ (reduced production) = thalassemia intermediate; heterozygotes = thalassemia trait/minor

Molecular Basis of Alpha-Thalassemia

• Deletions of alpha-globin genes (chromosome 16) are the predominant cause; point mutations are rare
• Normal genotype has four functional α-globin genes (αα/αα)
• Gene deletions occur in a stepwise fashion: deletion of one α-gene (--/αα) produces α-thalassemia trait; two genes (--/--) causes HbH disease; three genes (--/-α) causes α-thalassemia major (Hb Bart hydrops); four genes (--/--) is incompatible with life in utero
• Excess β-globin chains form tetramers (β4 = Hemoglobin H [HbH]) or γ-globin tetramers (γ4 = Hemoglobin Bart [Hb Bart])
• These abnormal hemoglobins are unstable, precipitate, and form inclusion bodies (precipitated globin chains visible on supravital staining as "golf ball" inclusions), leading to hemolysis and membrane damage

Cascade of Hemolytic Complications

• Intrinsic RBC defects: Oxidative damage from free globin chains, membrane protein cross-linking, band 3 alterations, phosphatidylserine exposure triggering complement activation (C3b deposition) and macrophage recognition
• Splenic sequestration and destruction of damaged erythrocytes → splenomegaly
• Intravascular and extravascular hemolysis → release of heme, hemoglobin, and iron → tissue iron deposition and oxidative damage
• Ineffective erythropoiesis: Massive erythroid hyperplasia in bone marrow and extramedullary hematopoiesis (spleen, liver, lymph nodes) with death of erythroid precursors before maturation due to oxidative stress and apoptosis
• Loss of erythrocytes exceeds RBC production despite compensatory erythropoietin response, resulting in chronic hemolytic anemia

Iron Overload Mechanism (Secondary Hemochromatosis)

• Free iron (non-transferrin-bound iron [NTBI]) released from hemolysis catalyzes reactive oxygen species (ROS) formation via Fenton reactions
• Iron-induced lipid peroxidation damages myocardial, hepatic, pancreatic, and endocrine tissues
• In transfusion-dependent patients, each unit of PRBC contains ~250 mg iron; combined with hemolytic iron load, this rapidly overwhelms the body's iron storage capacity (normal excretion ~1 mg/day)
• Iron deposition in cardiac myocytes → arrhythmias and heart failure; hepatic cirrhosis and fibrosis; pancreatic β-cell destruction → diabetes mellitus; anterior pituitary damage → hypogonadism and growth hormone deficiency

Additional Hemoglobin Abnormalities

• Fetal hemoglobin (HbF, α2γ2) production may persist or be reactivated; HbF is protective in β-thalassemia because γ-globin chains pair with excess α-chains, reducing free α-chain precipitation
• Hemoglobin A2 (α2δ2) levels are typically elevated in β-thalassemia (>3.5%) because δ-globin gene expression is not impaired

Beta-Thalassemia Genetic Mutations

• Point mutations affecting the β-globin coding sequence (e.g., codon 6 [sickle mutation region], codon 39), splice sites (most common type), promoter regions (TATA box mutations), or polyadenylation signals
• Deletions of various sizes removing part or all of the β-globin gene
• Insertions disrupting the reading frame
• Mediterranean ancestry (Greeks, Italians, Spanish) — highest prevalence in certain regions (e.g., Sardinia up to 16% carrier rate)
• Middle Eastern, North African, and West African ancestry
• Autosomal recessive inheritance — both parents must be carriers for homozygous disease

Alpha-Thalassemia Genetic Deletions

• Single α-gene deletion (--α/αα): Southeast Asian, African, Mediterranean populations
• Bi-allelic deletions (--/-- or --/-α): primarily Southeast Asian (Thai, Cambodian, Laotian, Vietnamese), Chinese, and Filipino populations
• Rare point mutations in α-globin genes (α1 or α2)
• Autosomal recessive inheritance for symptomatic disease
• Population-specific deletion patterns: Southeast Asia uses term "--SEA" (Southeast Asian deletion); Mediterranean "--MED"; African "--AF" or "--FSAS" (Far Southeast Asian specific)

Risk Factors for Disease Severity

• Homozygous or compound heterozygous genotype (two affected alleles)
• Type of mutation (β0 worse than β+; complete deletions worse than partial)
• Presence of HbF-promoting polymorphisms (protective)
• Genetic background (Xmn1 polymorphism near γ-globin promoter increases HbF levels)

Beta-Thalassemia Major (Transfusion-Dependent)

• Severe hemolytic anemia manifesting in infancy after 6-8 weeks of life (as fetal hemoglobin declines and β-globin chains are needed): marked pallor, jaundice, hepatosplenomegaly
• Growth retardation and developmental delay due to anemia and metabolic demands
• Bone pain and pathologic fractures from massive extramedullary hematopoiesis and osteoporosis
• Facial deformities (chipmunk facies, frontal bossing, maxillary prominence) from erythroid hyperplasia extending into maxillary sinus and skull — "crew-cut" appearance on skull X-ray from widened diploic space
• Cardiac complications: palpitations, dyspnea, syncope, arrhythmias from chronic anemia plus iron-induced cardiomyopathy (dilated, restrictive, or arrhythmogenic)
• Endocrine dysfunction: diabetes mellitus (10-15% by age 16), hypogonadism, growth hormone deficiency, hypothyroidism, hypoparathyroidism from iron deposition in pancreas and pituitary
• Splenomegaly (massive, up to 20 cm) with risk of splenic infarction and acute abdomen
• Transfusion requirements: 2-3 units PRBC every 2-4 weeks (higher in those with poor fetal hemoglobin production)
• Leg ulcers (especially over medial malleoli) from chronic hemolysis and vasculitis
• Pigmented gallstones from chronic hyperbilirubinemia

Beta-Thalassemia Intermediate

• Moderate hemolytic anemia with hemoglobin typically 7-10 g/dL
• Splenomegaly but may compensate partially without transfusions
• Similar skeletal deformities as major but less severe
• Variable transfusion requirement (some transfusion-independent)
• Risk of iron overload despite lower transfusion frequency

Beta-Thalassemia Trait/Minor (Heterozygous Carriers)

• Asymptomatic or mild hypochromic microcytic anemia (Hb 11-14 g/dL)
• Hemoglobin A2 elevated (3.5-7%) — diagnostic hallmark
• Normal lifespan and normal development
• Risk of confusion with iron deficiency anemia — must differentiate using serum ferritin, iron studies, HbA2 level

Alpha-Thalassemia Trait (Single Gene Deletion)

• Asymptomatic, mild or absent anemia
• Microcytic, hypochromic RBCs with normal or near-normal hemoglobin
• May have 1-2% HbH inclusions on supravital staining (incidental finding)
• No clinical symptoms

HbH Disease (Three Gene Deletions)

• Moderate hemolytic anemia (Hb 7-10 g/dL) presenting in early childhood
• Splenomegaly — often massive
• Jaundice from chronic hyperbilirubinemia
• Bone deformities similar to β-thalassemia major but typically less severe
• Gallstones from bilirubin precipitation
• Transfusion-independent or minimally transfusion-dependent
• Hemoglobin H (β4 tetramers) visible on supravital staining as "golf ball" inclusions (pathognomonic finding)
• Splenectomy-responsive — hemoglobin improves by 1-2 g/dL post-splenectomy
• Normal lifespan with appropriate management (most patients live into their 6th-7th decade)

Hemoglobin Bart Hydrops Fetalis (Four Gene Deletions) — Intrauterine Lethal

• Severe intrauterine anemia (Hb 2-5 g/dL)
• Hydrops fetalis: massive hepatosplenomegaly, ascites, pleural effusion, pericardial effusion, edema
• Hemoglobin Bart (γ4 tetramers, 80%) — useless oxygen-carrier (P50 extremely low, cannot unload oxygen)
• Fetal death in utero (typically third trimester) or neonatal death within hours of birth due to severe hypoxemia
• Maternal toxemia from massive placental dysfunction

Laboratory and Morphologic Correlates

• Marked hypochromia and microcytosis on peripheral blood smear (MCV typically <70 fL in major, <75 fL in trait)
• Target cells (codocytes) and polychromasia
• Nucleated RBCs in peripheral blood (immature release from marrow)
• Reticulocytosis reflecting bone marrow compensation
• Rouleaux formation from increased immunoglobulins (IgG, IgM)

Peripheral Blood Smear Morphology

• Microcytic, hypochromic RBCs with low MCH and MCV
• Target cells (codocytes) — characteristic finding due to excess membrane relative to hemoglobin content, creating central staining dot surrounded by pale halo
• Polychromasia from reticulocytosis
• Nucleated RBCs in major forms
• RBC fragmentation and schistocytes from oxidative damage
• Howell-Jolly bodies (nuclear remnants) if asplenic
• Heinz bodies (precipitated globin chains) on supravital staining (brilliant cresyl blue or new methylene blue) — "golf ball" appearance in HbH disease
• Rare hypochromic microcytic RBCs with preserved or high RBC count (key discriminator: RBC count typically elevated or normal in thalassemia, low in iron deficiency)

Bone Marrow Examination (If Needed)

• Erythroid hyperplasia with increased erythroid:myeloid (E:M) ratio (up to 10:1, normal 3-4:1)
• Dysplastic changes: nuclear-cytoplasmic asynchrony, abnormal nuclear morphology, irregular membranes
• Increased apoptosis of erythroid precursors
• Iron-laden macrophages (hemosiderin-laden, Prussian blue positive) reflecting iron overload

Complete Blood Count and RBC Indices

• Hemoglobin: thalassemia major 6-9 g/dL; intermediate 7-10 g/dL; trait 11-14 g/dL
• MCV: consistently low (<70 fL in major, <75 fL in trait)
• MCH: reduced (often disproportionately low relative to anemia severity — key diagnostic clue)
• MCHC: reduced
• RBC count: typically normal or elevated (unlike iron deficiency where RBC count is low) — "RBC count out of proportion to hemoglobin"
• Reticulocyte count: elevated (>5% in major forms, 1-3% in trait)
• WBC: may be elevated from extramedullary hematopoiesis
• Platelets: may be elevated; increased thrombotic risk

Hemoglobin Electrophoresis and HPLC (High-Performance Liquid Chromatography)

• Beta-Thalassemia Major:
• HbA (α2β2): absent (β0) or markedly reduced (<10% in β+)
• HbA2 (α2δ2): elevated (3.5-7%, normal <3.5%)
• HbF (α2γ2): elevated (10-90%, often >50%)
• Pattern: HbF + HbA2 ± small HbA — diagnostic pattern
• Beta-Thalassemia Intermediate:
• HbA: reduced (10-30%)
• HbA2: elevated
• HbF: elevated (5-15%)
• Beta-Thalassemia Trait:
• HbA: normal or slightly reduced
• HbA2: elevated (3.5-7%) — hallmark finding
• HbF: normal (<1%)
• HbA2/HbF ratio >2 (helps differentiate from HPFH or HbE thalassemia)
• Alpha-Thalassemia: hemoglobin electrophoresis is normal in trait and most cases; diagnosis primarily by clinical/genetic means
• HbH disease: HbH (β4) visible as distinct peak (5-30%); also Hb Bart in newborns
• Supravital staining showing HbH inclusions is confirmatory

Serum Iron Studies

Immediate stabilisation

• Symptomatic severe anemia (Hb crash from aplastic crisis, splenic sequestration, or hyperhemolysis): packed RBC transfusion, cross-matched and leukoreduced, with extended phenotype matching (at minimum Rh and Kell) to limit alloimmunization — the standard endorsed by the Thalassemia International Federation (TIF) guidelines.
• Hb Bart hydrops fetalis: intrauterine transfusion is the only intervention that has produced survivors; otherwise the focus is prenatal diagnosis and counselling, and surveillance for maternal mirror syndrome/pre-eclampsia.

First-line chronic therapy

• Regular transfusion program (transfusion-dependent β-thalassemia major, some HbH disease): TIF recommends maintaining a pre-transfusion hemoglobin around 9–10.5 g/dL, which suppresses the erythropoietin drive, shuts down ineffective erythropoiesis, and prevents skeletal deformity and extramedullary masses.
• Folic acid: replaces the substrate consumed by high-turnover erythropoiesis; standard in all hemolytic states.
• Iron chelation: mandatory once transfusional loading begins (TIF suggests starting after roughly the first 10–20 units or when ferritin is persistently elevated).
• Oral chelators: deferasirox (once-daily, first-line in the US), deferiprone (best cardiac iron removal).
• Parenteral: deferoxamine by prolonged subcutaneous infusion; used in combination for severe cardiac loading.

Escalation / second line

• Erythroid maturation agents: luspatercept, a TGF-β superfamily ligand trap, is FDA-approved to reduce transfusion burden in adults with transfusion-dependent β-thalassemia.
• Hydroxyurea: HbF induction, used mainly in non-transfusion-dependent thalassemia; evidence is weaker than in sickle cell disease.

Definitive and surgical management

• Allogeneic hematopoietic stem cell transplant: curative; best outcomes in young, matched-sibling recipients before iron-related organ damage.
• Gene therapy: lentiviral β-globin gene addition and CRISPR-based BCL11A editing (HbF de-repression) are FDA-approved for transfusion-dependent β-thalassemia.
• Splenectomy: reserved for hypersplenism with escalating transfusion needs; deferred when possible, and preceded by pneumococcal, meningococcal, and Haemophilus influenzae type b vaccination per CDC/ACIP.

Contraindicated

• Empiric iron supplementation — thalassemia is iron-replete or overloaded; give iron only for documented deficiency.
• ACE inhibitor-style reflex prescribing is irrelevant here; the true trap is iron. Also avoid deferasirox in significant renal impairment and oxidant drugs in unstable HbH disease.

Complications of the disease

• Iron-overload cardiomyopathy (emergency): non-transferrin-bound iron enters myocytes through L-type calcium channels, driving Fenton-reaction free radical injury; presents as dilated or restrictive cardiomyopathy, heart failure, or ventricular arrhythmia. Signalled by falling ejection fraction and a **short cardiac T2\* on MRI**; it remains the leading cause of death.
• Endocrinopathy: iron deposition in pancreatic β cells and the anterior pituitary → diabetes mellitus, hypogonadotropic hypogonadism, growth failure, hypothyroidism, hypoparathyroidism. Signalled by delayed puberty and abnormal fasting glucose/HbA1c (note HbA1c is unreliable with high RBC turnover).
• Cirrhosis and hepatocellular carcinoma: hepatic iron plus transfusion-acquired hepatitis C.
• Aplastic crisis from parvovirus B19 (emergency): transient arrest of erythroid precursors in a patient with no marrow reserve → abrupt hemoglobin drop with reticulocytopenia.
• Acute splenic sequestration / splenic infarction (emergency): rapidly enlarging spleen, hypovolemia, plummeting hemoglobin.
• Pigment gallstones and cholecystitis; chronic leg ulcers over the malleoli.
• Extramedullary hematopoiesis: paraspinal masses can cause spinal cord compression (emergency); skull and facial marrow expansion produces the crew-cut skull and chipmunk facies.
• Hypercoagulability: phosphatidylserine-exposing erythrocytes and post-splenectomy thrombocytosis → venous thrombosis and pulmonary hypertension, especially in non-transfusion-dependent disease.

Complications of treatment

• Transfusion: alloimmunization with delayed hemolytic reactions, febrile and allergic reactions, TRALI/TACO (emergencies), and transfusional iron loading itself.
• Deferiprone — agranulocytosis (emergency): any fever mandates immediate ANC measurement and drug hold; weekly ANC monitoring is standard.
• Deferasirox: acute kidney injury, hepatic failure, and GI hemorrhage (boxed warnings); monitor creatinine and transaminases.
• Deferoxamine: ototoxicity, retinopathy, growth plate/skeletal effects in children, and predisposition to Yersinia enterocolitica sepsis (siderophore-utilising organism) (emergency).
• Post-splenectomy overwhelming sepsis with encapsulated organisms (emergency).

• Microcytosis out of proportion to the anemia, with a normal or high RBC count, is the single most reliable clue that separates thalassemia trait from iron deficiency. The Mentzer index (MCV ÷ RBC) is <13 in thalassemia trait, >13 in iron deficiency.
• The best next step in a microcytic patient with normal iron studies is hemoglobin electrophoresis/HPLC. An elevated HbA2 clinches β-thalassemia trait; a normal electrophoresis in a microcytic, iron-replete patient points to α-thalassemia trait, which is diagnosed by exclusion or by α-globin gene testing.
• Do not give iron. Prescribing iron to a "microcytic anemia" that is actually thalassemia trait is the classic distractor and accelerates iron loading.
• Timing is the tell: β-thalassemia major becomes symptomatic at around 6 months of age as the γ→β switch completes and protective HbF wanes; α-thalassemia is symptomatic in utero or at birth because α-chains are needed in fetal life.
• ***Golf-ball\/inclusion bodies* on supravital stain (brilliant cresyl blue) = HbH disease** (β4 tetramers). Hb Bart (γ4) on newborn screening signals α-thalassemia; Bart hemoglobin has extremely high oxygen affinity and cannot unload O₂.
• Cis versus trans matters for counselling: Southeast Asian carriers typically have both deletions on one chromosome (cis, --/αα) and can produce hydrops fetalis offspring; African-ancestry carriers usually carry them in trans (-α/-α) and cannot.
• Coexisting iron deficiency can normalise HbA2 and mask β-thalassemia trait — repeat the electrophoresis after iron repletion.
• The association examiners love: iron-overload cardiomyopathy is the leading cause of death, and chelation — not transfusion frequency alone — determines survival. Skull films showing a crew-cut diploic space and chipmunk facies reflect marrow expansion from ineffective erythropoiesis, not iron.
• Carrier screening: ACOG recommends CBC with red cell indices, and hemoglobin electrophoresis when indices are low, as part of preconception and prenatal screening.