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Epidemiology and Disease Pathophysiology: Thalassaemia
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  1. Epidemiology and Disease Pathophysiology: Thalassaemia Ali T. Taher, MD Professor Department of Internal Medicine American University of Beirut Medical Center Beirut, Lebanon

  2. Overview • Definition • Etiology • Imbalance of globin chain synthesis • Molecular basis • Differentiation of thalassaemia major and thalassaemia intermedia • Epidemiology • Pathophysiology • Diagnosis • Clinical manifestations • Complications • Prognosis • Management of iron overload

  3. Definition • The thalassaemias comprise a heterogeneous group of disorders of haemoglobin production • Normal haemoglobin production partially or completely suppressed due to defective synthesis of 1 or more components of the globin chains • Depending on the involved genes, the defect is classified as ‑thalassaemia or ‑thalassaemia • Under normal conditions, the red cells of the adult human contain approximately 98% HbA, traces of HbF, and 2.0% HbA2 Cappellini N, et al, eds. Thalassaemia International Federation; 2000.

  4. Clinical Forms of β-Thalassaemia • Thalassaemia major (TM) • Presents in the first year of life • Subsequently requires regular transfusions and iron chelation to survive • Thalassaemia intermedia (TI) • Presents later in life • May be transfusion independent or require only sporadic transfusions Olivieri NF. N Engl J Med. 1999;341:99.

  5. Thalassaemia MajorClinical Features • Clinical manifestations of anaemia emerge at 6 months–2 years • Infants protected by prenatal HbF production • Typical presentation includes • Pallor • Irritability • Growth retardation • Enlargement of the liver and spleen • Jaundice • If untreated • Facial and skeletal changes result from bone marrow expansion • Average survival <4 years Forget BG. In Hoffman: Hematology: Basic Principles and Practice, 2005.

  6. Thalassaemia Major Molecular Basis • Patients with β-thalassaemia major have inherited two β-thalassaemia alleles • Located on each copy of chromosome 11 • Hypochromic, abnormally shaped red blood cells • Contain significantly reduced amounts of haemoglobin than normal blood cells because of diminished HbA synthesis • Deposition of precipitated aggregates of free α-globin chains results in accumulation • Damages erythrocytes, precursor cells in bone marrow • Resulting anaemia so severe that patients usually require chronic blood transfusions Forget BG. In Hoffman: Hematology: Basic Principles and Practice, 2005.

  7. Thalassaemia IntermediaClinical Features TI has an extraordinarily wide clinical spectrum, unlike TM, which presents with severe anaemia requiring frequent blood transfusions • Mild TI • Completely asymptomatic • until adulthood • Severe TI • Presentation between 2 and 6 years • Retarded growth and development Cappellini N, et al, eds. Thalassaemia International Federation; 2000.

  8. Molecular Basis of Thalassaemia Intermedia • 3 main reasons • Inheritance of a mild (β+) mutation • Presence of a polymorphism for the enzyme Xmn-I in the G- promoter region, associated with increased HbF • Coinheritance of -thalassaemia • Increase production of alpha-globin chains by • Triplicated alpha genotype associated to beta-heterozygosity • Interaction of beta and delta beta thalassaemia Taher A. Blood Cells Mol Dis. 2006;37:12.

  9. Helpful Clues to Differentiate Major from Intermedia Thalassaemia Major Thalassaemia Intermedia More Likely More Likely Clinical Presentation (years) <2 >2 Hb levels (g/dL) 6–7 8–10 Liver/spleen enlargement Severe Moderate to severe Haematologic HbF (%) >50 10–50 (may be up to 100%) HbA2 (%) <4 >4 Genetic Parents Both carriers of high HbA2 1 or both atypical carriers:-thalassaemia - High HbF -thalassaemia - Borderline HbA2 Molecular Type of mutation Severe Mild/silent Coinheritance of -thalassaemia No Yes Hereditary persistence of fetal haemoglobin No Yes -thalassaemia No Yes G XmnI polymorphism No Yes Cappellini N, et al, eds. Thalassaemia International Federation 2000 with permission.

  10. Epidemiology • Approximately 7% of the world’s population is a carrier of haemoglobin disorders1 • Between 300,000 and 500,000 infants are born every year with severe homozygous forms of the disease1 • An overview of the global distribution of thalassaemias shows that in addition to the Mediterranean countries in which they were first recognized, thalassaemias are frequently found in Asia and the Far East2 • Population migration has led to spread of this condition with its morbidity and mortality2 1. Weatherall D, et al. Disease Control Priorities in Developing Countries, 2006. 2. Cappellini N, et al, eds. Thalassaemia International Federation; 2000.

  11. Thalassaemia—Global Distribution Due to the continual migration of populations from one area to another, there is virtually no country of the world now in which thalassaemia does not affect some percentage of the inhabitants Cappellini N, et al, eds. Thalassaemia International Federation 2000, with permission.

  12. β-Thalassaemia Genes, Severity and Ethnic Distribution Cappellini N, et al, eds. Thalassaemia International Federation 2000 with permission.

  13. Thalassaemia: Clinical Manifestations and Treatment

  14. Pathophysiologic Sequelae of Untreated Thalassaemia and Corresponding Clinical Manifestations Excess free -globin chains Formation of haeme and haemichromes DenaturationDegradation Iron-mediated toxicity Haemolysis Ineffectiveerythropoiesis Membranebinding ofIgG and C3 Removal ofdamaged red cells Splenomegaly Increasederythropoietinsynthesis Anaemia Reduced tissueoxygenation Skeletaldeformities,osteopaenia Iron overload Erythroidmarrowexpansion Increased Iron absorption Olivieri NF. N Engl J Med. 1999;341:99. .

  15. Clinical Manifestations With permission from Dr. Cappellini.

  16. Clinical Manifestations • Thalassaemia trait has no important clinical effects • Activity of the normal β gene on the allelic chromosome makes enough stable globin • However, inheritance of 2 defective β-globin genes causes a wide spectrum of clinical conditions • Molecular studies reveal a wide array of abnormalities, which underlie above phenotypes and help in their identification Cappellini N, et al, eds. Thalassaemia International Federation; 2000.

  17. Complications • Thalassaemia major complications mostly due to iron overload and frequent blood transfusions • Heart failure • Infection (blood transfusion, postsplenectomy) • Hypogonadism and infertility • Diabetes mellitus • Hypothyroidism • Thalassaemia intermedia complications include • Thrombosis • Pulmonary hypertension • Leg ulcers • Extramedullary haematopoiesis • Endocrine disorders (osteoporosis, hypogonadism) Olivieri NF. N Engl J Med. 1999;341:99. Taher A, et al. Blood Cells Mol Dis. 2006;37:12.

  18. Prevalence of Common Complications in TI vs TM in Italy and Lebanon Thalassaemia ThalassaemiaComplication (% of TI, Lebanon TI, Italy Major, Lebanon Major, ItalyPatients Affected) (n = 37) (n = 63) (n = 40) (n = 60) Splenectomy 90 67 95 83 Cholecystectomy 85 68 15 7 Gallstones 55 63 10 23 EMH 20 24 0 0 Leg ulcers 20 33 0 0 Thrombotic events 28 22 0 0 Cardiopathy* 3 5 10 25 PHT 50† 17 10 11 Abnormal liver enzymes 20 22 55 68 Hepatitis C virus infection 7 33 7 98 Hypogonadism 5 3 80 93 Diabetes mellitus 3 2 12.5 10 Hypothyroidism 3 2 15 11 *Fractional shortening <35%. †PHT was defined as pulmonary artery systolic pressure >30 mmHg. A well enveloped tricuspid regurgitant jet velocity could be detected in only 20 patients, so frequency was assessed in these patients only. Taher A, et al. Blood Cells Mol Dis. 2006;37:12.

  19. Iron Overload • Iron overload occurs when iron intake is increased over a sustained period of time • Transfusion of red blood cells (thalassaemia major) • Increased absorption of iron from the digestive tract (thalassaemia intermedia) • Because there is no mechanism in humans to excrete the excess iron, this has to be removed by chelation therapy Forget BG. In Hoffman: Hematology: Basic Principles and Practice, 2005.

  20. Iron Overload • 1 unit of blood contains approximately 200–250 mg of iron1 • Chronic transfusion-dependent patients have an iron excess of ~ 0.32–0.64 mg/kg/d2 • With repeated infusions, iron accumulates • Signs of iron overload can be seen after anywhere from 10 to 20 transfusions, such as in thalassaemia major patients2 • Iron overload can lead to early mortality2 1. Andrews NC. N Engl J Med. 1999;341:1986. 2. Porter JB. B J Haematol. 2001;115:239.

  21. Iron Overload • Normal intestinal iron absorption is about 1–1.5 mg/d • In thalassaemic patients who do not receive any transfusion,ironabsorption increases • In individuals who are poorly transfused, absorption rises to 3–4 mg/d or more • This represents a supplementary 1–2 g of iron loading per year Cappellini N, et al, eds. Thalassaemia International Federation 2000.

  22. Evaluation of Iron Overload • Serum ferritin concentration • Noninvasive • Accuracy in iron overload questionable • Liver iron concentration (LIC) • Liver biopsy • Reference standard • SQUID • Noninvasive, availability limited • MRI • Noninvasive, FDA-approved technique • Others: NTBI and T2*MRI Olivieri N, Brittenham G. Blood. 1997;89:739.

  23. β-Thalassaemia MajorTreatment • Conventional treatment/chelation • The gold standard treatment has been the administration of blood transfusions and subsequent iron chelation therapy • Bone marrow transplantation (BMT) • BMT has been attempted from donors with matching alleles • HbF-inducing therapy • Gene therapy—the future Olivieri NF. N Engl J Med. 1999;341:99.

  24. Conclusions • Thalassaemias heterogeneous group of disorders of haemoglobin production • β-TM present in first year of life, requires transfusions • β-TI later presentation, may not require transfusion therapy • Iron overload may be present in both conditions, caused by transfusion therapy or excess GI iron absorption • Current treatment involves chelation therapy