MOLECULAR BASIS OF THALASSEMIAChris Chan (chrishw.chan@utoronto.ca)

Louis Chiu (louis.chiu@utoronto.ca)

Lok Tin Liu (loktin.liu@gmail.com)

Janet Lui (janet.lui@utoronto.ca)

Signed Up Presentation Date: January 13th, 2010

PHM 226, 2010Instructor: Dr. Jeffrey Henderson

THALASSEMIA:THALASSA (SEA) HAIMA (BLOOD)

‘Mediterranean Anemia’- 1st published in 1925

Genetic autosomal recessive blood disease Reduced rate of synthesis of globin chains in

hemoglobin Decreased oxygen carrying capacity of

hemoglobin: Anemia

HEMOGLOBIN A

Fetal Hemoglobin (2 alpha, 2 gamma)

Hemoglobin A2 (2 alpha, 2 delta) Small amounts in body

α

αβ

β

ALPHA THALASSEMIA

Alpha Thalassemia: deficient/absent alpha subunits Excess beta subunits Excess gamma subunits newborns

Tetramers formed: Hemoglobin H adults Hemoglobin Bart’s newborns

Five types: Silent Carrier Trait (Minor) Hemoglobin H Disease Major (Hemoglobin Bart’s) Hemoglobin Constant Spring

β/γ

β/γ

β/γ β/

γ

GENETIC BASIS OF ALPHA THALASSEMIA

Encoding genes on chromosome 16 (short arm) Each cell has 4 copies of the alpha globin gene

Each gene responsible for ¼ production of alpha globin

4 possible mutation states: Loss of ONE gene silent carrier Loss of TWO genes thalassemia minor (trait) Loss of THREE genes Hemoglobin H

Accumulation of beta chains Association of beta chains in groups of 4 Hemoglobin H

Loss of FOUR genes Hemoglobin Barts NO alpha chains produced ∴ only gamma chains present Association of 4 gamma chains Hemoglobin Barts

CLINICAL OUTCOMES OF ALPHA THALASSEMIA

Silent carriers • asymptomatic • “normal”

Alpha Thalassemia minor (trait)• no anemia• microcytosis

-unusually small red blood cells due to fewer Hb in RBC• “normal”

Alpha Thalassemia intermedia (“Hemoglobin H”)• microcytosis & hemolysis (breakdown of RBC)

- results in severe anemia• bone deformities• splenomegaly (enlargement of spleen)• “severe and life threatening”

CLINICAL OUTCOMES OF ALPHA THALASSEMIA

Alpha Thalassemia major• Hb Bart’s • fatal hydrops fetalis

- fluid build-up in fetal compartments, leads to death

• occurs in utero Hemoglobin Constant Spring

• most common form of alpha thalassemic defects in Southeast Asia

• similar to HbH but no microcytosis• anemia is more severe than other alpha thalassemic

variants• greater growth delay than HbH patients

TREATMENTS FOR ALPHA THALASSEMIA

Silent Carrier – no treatment req’d Hemoglobin Constant Spring – form of Silent Carrier – no

treatment req’d Trait (Minor) – no treatment req’d Hemoglobin H Disease – Folate

avoid iron supplements avoid sulfa drugs (already prone to hemolytic crises), and

other drugs/combinations that may increase risk of hemolytic anemia

Major (Hemoglobin Bart’s) –RBC transfusion while still in womb, else fetus is stillborn or dies shortly

BETA THALASSEMIA

Beta Thalassemia: deficient/absent beta subunits 200 point mutations possible, deletions less likely In any region with high levels of thalassemia, one

or two mutations predominate, but DIFFERENT mutations were found in different populations

Commonly found in Mediterranean, Middle East, Asia, and Africa

Three types: Trait Intermedia Major (Cooley anemia)

May be asymptomatic at birth as HbF functions

GENETIC BASIS OF BETA THALASSEMIA Encoding genes on chromosome 11 (short arm) Each cell contains 2 copies of beta globin gene

beta globin protein level = alpha globin protein level Suppression of gene more likely than deletion

2 mutations: beta-+-thal / beta-0-thal “Loss” of ONE gene thalassemia minor (trait) “Loss” of BOTH gene complex picture

2 beta-+-thal thalassemia intermedia / thalassemia major

2 beta-0-thal thalassemia major beta-+-thal / beta-0-thal thalassemia major

Excess of alpha globin chains

CLINICAL OUTCOMES OF BETA THALASSEMIA

Beta Thalassemia minor (trait)• asymptomatic • microcytosis• minor anemia

Beta Thalassemia intermedia• symptoms similar to Cooley Anemia but less severe

Beta Thalassemia major (Cooley Anemia)• most severe form • moderate to severe anemia• intramedullary hemolysis (RBC die before full development)• peripheral hemolysis & splenomegaly• skeletal abnormalities (overcompensation by bone marrow)• increased risk of thromboses • pulmonary hypertension & congestive heart failure

TREATMENT FOR BETA THALASSEMIA

Trait – no treatment req’d Intermedia Major (Cooley anemia)

Regular folate supplementation RBC transfusion (Splenectomy may decrease need for

transfusions) to maintain [Hgb] ~9-10g/dL Increased GI iron absorption due to low levels of

hepcidin Normally inhibits ferroportin (transmembrane

transporter for iron-storing/-transporting cells) Increased ferroportin activity increases iron uptake from

GI by duodenal enterocytes Blood transfusions iron accumulation iron

overload

IRON OVERLOAD & TREATMENT

Iron overload - the liver becomes fully loaded with iron, and subsequent accumulation in and damage to other organs and tissues occurs

Iron chelating agents – bind to free iron, increasing solubility and facilitating excretion Deferoxamine (Desferal) – IV or subcutaneous Deferasirox (Exjade) – oral suspension tablet Deferiprone (Ferriprox) oral

no longer licensed for use in Canada ?

DEFEROXAMINE MESYLATE

Desferal – by Novartis IV or subcutaneous (IM is ok), poor oral absorption First line, complexes with iron ferrioxamine

(water soluble) excreted through kidney

Image from: http://en.wikipedia.org/wiki/Deferoxamine

DEFERASIROX Exjade – Novartis

Oral suspension tablet High iron affinity Biliary excretion via glucoronidation

Image from: http://en.wikipedia.org/wiki/Deferasirox

DEFERIPRONE

Ferriprox – by Apotex Indicated for treating iron overload in patients

with thalassemia major when desferoxamine is contraindicated/inadequate Combination therapy of desferoxamine + deferiprone

is more effective than monotherapy

BUT, it is no longer licensed for use in Canada Interesting read:

Controversy between Apotex & Sick Kid’s Hospital physician-researcher Nancy Olivieri Reported to lead to progressive hepatic fibrosis

(disputed) http://firstclinical.com/journal/2009/0902_Olivieri.pdf Google: apotex, olivieri, ferriprox

Image from: http://en.wikipedia.org/wiki/Deferiprone

REFERENCESButler, C. (2009). About Thalassemia. Cooley’s Anemia Foundation. Retrieved from:

http://www.thalassemia.org/index.php?option=com_content&view=article&id=19&Itemid=27

Conran, N., & Costa, F. (2009) Hemoglobin disorders and endothelial cell interactions. Clinical Biochemistry, 42, 1824-1838

e-Therapeutics (2009). Exjade. Retrieved from e-CPS Online Product Monograph

e-Therapeutics (2010). Desferal. Retrieved from e-CPS Online Product Monograph

Hemoglobin Synthesis. (2002). Retrieved Jan. 9, 2010, from http://sickle.bwh.harvard.edu/hbsynthesis.html

Ho, P. J., & Thein, S. L. (2000). Gene regulation and deregulation: a globin perpsective. Blood Reviews, 17, 78-93

Lexi-Comp (2010). Deferasirox. Retrieved from Lexi-Drugs Online database

Lexi-Comp (2010). Deferoxamine. Retrieved from Lexi-Drugs Online database

Thalassemia Overview. (1999). Retreived Jan. 9, 2010 from http://sickle.bwh.harvard.edu/thalover.html

Rassi, F.E, Cappellini, M.D., Inati, A., Taher, A. (2008) Beta-thalassemia intermedia: An overview. Pediatric Annals, 37 (5), 322-329

Singer, S.T. et al (2009) Hemoglobin H-constant spring in North America: An alpha thalassemia with frequent complications. American Journal of Hematology, 84(11), 759-761

Weatherall, D.J. (2004). Thalassemia: the long road from bedside to genome. Nature, 5, 1-7

Muncie, HL Jr, Campbell, J. (2009).  Alpha and beta thalassemia. Am Fam Physician, 80 (4), 339-44. Schrier, SL. (1994). Thalassemia: pathophysiology of red cell changes. Annu Rev Med , 45, 211-8.

Ceci, A., Felisi, M., De Sanctis, V., & De Mattia, D. Pharmacotherapy of iron overload in thalassaemic patients [Abstract]. Expert Opinion on Pharmacotherapy, 4(10), 1763-1774.

Roberts D, Brunskill S, Doree C, Williams S, Howard J, Hyde C. Oral deferiprone for iron chelation in people with thalassaemia. Cochrane Database of Systematic Reviews 2007, Issue 3. Art. No.: CD004839. DOI: 10.1002/14651858.CD004839.pub2.

Thompson Reuters. (2009). Thalassemia – Chronic. Retrieved from http://www.thomsonhc.com.myaccess.library.utoronto.ca/hcs/librarian/PFActionId/hcs.external.RetrieveDocument/eid/112153002/DocId/CR2016C/ContentSetCode/DISEASEDEX-GMCR#drugTreatmentSection

SUMMARY Alpha Thalassemia

Lack of alpha globins & excess beta globins; mostly result of deletions

Loss of 1 gene Silent Carrier “Normal” Loss of 2 genes Alpha Thalassemia minor “Normal” Loss of 3 genes Hemoglobin H “severe & life threatening”

Folate Loss of 4 genes Hemoglobin Barts mostly fatal RBC

transfusions Beta Thalassemia

Lack of beta globins & excess alpha globins; mostly result of point mutations

1 gene mutated Beta Thalassemia minor “Normal” 2 genes mutated clinical outcomes determine diagnosis

(Thalassemia Intermedia or Cooley Anemia) regular Folate Supplementation & RBC transfusions

Side Effect of Chronic RBC Transfusions Iron Overload Treat with iron chelating agents (Deferoxamine, Deferasirox, Deferiprone)

ALSO INFORMATION ON SLIDES 2, 6, 7 AND 13