1. Hemoglobinopathies- Part I
Nemer El Mouallem MD
VCU Health system
05/23/2018

2. Hemoglobin A structure
Tetramer -2 pairs of globin chains -Alpha-beta dimers aggregate to form tetramers Heme -Complex of Fe2+ and protoporphyrin -Covalently bound to each globin molecule -Reversibly binds one O2 molecule

3. Normal Hemoglobin found in adults
HbA : α2β %
HbA2: α2δ %
HbF: α2γ <1%

4. Human Globin Genes

5. Thalassemias Most common single gene Mendelian diseases
Disorders of the synthesis or structure of hemoglobin
Almost 1500 variants described

6. Thalassemias and Malaria

7. Hemoglobinopathies vs Thalassemias
Hemoglobinopathies: amino acid substitutions leading to an abnormal globin structure . Examples:
HbS
HbE
HbC
Thalassemias: reduced amounts or absence of a structurally normal globin chain
-Alpha thalassemias
-Beta thalassemias

8. Hemoglobinopathies vs Thalassemias
Interaction among the two are common:
Hemoglobin S/beta thalassemia
Hemoglobin S/alpha thalassemia
Hemoglobin E/beta thalassemia

9. Diagnostics Hb electrophoresis
Cellulose acetate (alkaline): ID’s HbA, HbF, HbS, HbD, HbE, HbC, HbO, HbH
Citrate agar (acidic): distinguishes Hb C from Hb E or Hb O
HPLC (High performance liquid chromatography)
Retention time, peak characteristics influenced by single aa substitutions
Accurately identifies 75% of Hb variants
Molecular biology
PCR, gene sequencing

10. Thalassemia mutations
Alpha thalassemias
Mostly caused by gene deletions
Clinically expressed in fetus and at birth
Beta thalassemias
Mostly caused by point mutations
Expressed several months after birth when switch from γ to β globin

11. Beta thalassemias
Decreased synthesis of beta globin genes  excess of alpha globin chains
Alpha globins aggregate to form insoluble inclusions in erythroid precusors
Intramedullary death of erythroid precursors: ineffective erythropoeisis

12. Beta thalassemias
Unpaired and unstable alpha globin chains and excess Fe cause:
Membrane lipid oxidation
Membrane protein damage
Decreased RBC deformability
Removal from circulation
 Membrane damage leads to polysaccharide exposure and hypercoagulability

13. Beta thalassemias
High degree of erythropoietic activity coupled with ineffective erythropoiesis  Death of erythroid precursors in the bone marrow
Hemolytic panel is positive though retic level not as high as expected
These phenomena are more evident in thalassemia major and intermedia

14. Beta thalassemias
β0 thal mutations: critical point mutation or deletion leading to no expression of beta globin
Β+ thal mutations : partial expression of beta globin chain

15. Beta thalassemias

16. Beta Thalassemias

17. Beta thalassemias

18. Beta thalassemias

19. Beta Thalassemia

20. Beta Thalassemia major
Clinical Features
Hematologic: severe microcytic anemia, splenomegaly, extramedullary hematopoiesis
Skeletal changes: expanded marrow cavity, thalassemic facies, osteopenia, thin cortex
Growth Retardation
Thrombembolism

21. Beta Thalassemia major
Cardiopulmonary: Myocardial Fe overload with arrhythmia, CHF, hemolytic pulmonary hypertension
Liver: Hepatic iron overload  fibrosis, cirrhosis. Pigmented gallstones
Endocrinopathies: DM, hypoparathyroidism, hypogonadism and delayed puberty
Transfusion related: infection, alloimmunization

22. Thalassemia major- iron overload
Each unit of blood contains ~ 225 mg of Fe

23. Thalassemia major- iron overload

24. Beta thalassemia major
Treatments
Comprehensive care centers, multi-speciality, strong social services
Hypertransfusion beginning 2nd or 3rd year: Maintain Hb >
Splenectomy for increasing transfusion requirement
Iron chelation starting after age 3 : keep liver iron < 5 mg/g
Consider: stem cell transplantation, hydroxyurea, prenatal diagnosis, gentic counseling

25. Iron Chelators Deferoxamine: Given by prolonged infusion
Deferasirox: once daily PO dosing , can remove cardiac iron
Deferiprone: Orally active, removes cardiac iron, limited use in US
Iron chelator related toxicities: growth delay, skin reactions, bone marrow suppression, renal/hepatic damage, Yersinia infections, agranulocytosis (Deferiprone)

26. Alpha Thalassemias
Decreased synthesis of alpha globin genes, excess of beta or beta like globin chains
Potential formation of abnormal hemoglobins
Hemoglobin barts: γ4
Hemoglobin H: β4

27. Alpha Thalassemias α+: deletion of a single gene on chromosome 16
α0: deletion of both genes on chromosome 16
Point mutations are less common, but phenotype more severe

28. Alpha Thalassemias

29. Alpha Thalassemias

30. Alpha Thalassemias Silent Carrier 3 of 4 alpha genes present
+/- mild anemia
Low MCV

31. Alpha Thalassemias Alpha thalassemia trait
2 of 4 alpha genes are present
Homozygous α+ or heterozygous α0
Clinical features: +/- mild anemias, MCV <78, Hb Barts 2-10% in newborns
Do not confuse with Fe deficiency anemia. Diagnosis of exclusion, confirm with molecular testing

32. Alpha Thalassemias Hemoglobin H disease β4 1 of 4 alpha genes present
20-40% Hb Barts in newborn and 5-40% HbH in adults
-visualized by brilliant cresyl blue
-Hb electrophoresis
-HPLC

33. Alpha thalassemias HbH disease- Clinical presentation:
Hemolytic anemia of varying degrees
Microcytosis
Splenomegaly
Ineffective erythropoiesis
Fe loading
Treatment: Transfusions for symptomatic anemia or severe anemia Hb <7 + iron chelation

34. Alpha thalassemias Hemoglobin Bart’s : Hydrops Fetalis
Intrauterine treatments: transfusions, stem cell transplant, improved perinatal care
After birth complications: Growth retardation, neurodevelopmental delays, lifelong transfusions, associated congential abnormalities
Genetic counseling and screening is important

35. Alpha Thalassemias
Fetus complications in absence of all alpha globin genes

36. Alpha Thalassemia- RBC indices

37. Atypical alpha thalassemias
Alpha thalassemia- mental retardation syndromes
ATR-16: alpha thal retardation associated with Ch 16
X-linked mutations in ATRX
Alpha thalassemia- MDS : acquired alpha thalassemia in MDS