2. Thalassemia
• At the end of this lecture, you will be introduced
to the thalassemias. You will learn about the
pathophysiology, clinical signs and symptoms,
laboratory test results, and treatments for both
the alpha and beta forms of
thalassemia. Subclasses of each major form of
thalassemia will be discussed.
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3. Thalassemia
• Diverse group of disorders which manifest
as anemia of varying degrees.
• Result of defective production of globin
portion of hemoglobin molecule.
• Distribution is worldwide.
• May be either homozygous defect or
heterozygous defect.
• Defect results from abnormal rate of
synthesis in one of the globin chains.
• It is an autosomal recessive syndrome
4. Thalassemia
• Results in overall decrease in amount
of hemoglobin produced and may
induce hemolysis.
• Two major types of thalassemia:
–Alpha (α) - Caused by defect in rate of
synthesis of alpha chains.
–Beta (β) - Caused by defect in rate of
synthesis in beta chains.
• May contribute protection against
5. Genetics of Thalassemia
• Adult hemoglobin composed two
alpha and two beta chains.
• Alpha thalassemia usually caused by
gene deletion; Beta thalassemia
usually caused by mutation.
• Results in microcytic, hypochromic
anemias of varying severity.
7. Classical Syndromes of Beta Thalassemia
• Silent carrier state – the mildest form of
beta thalassemia.
• Beta thalassemia minor - heterozygous
disorder resulting in mild hypochromic,
microcytic hemolytic anemia.
• Beta thalassemia intermedia - Severity lies
between the minor and major.
• Beta thalassemia major - homozygous
disorder resulting in severe transfusion-
8. Silent Carrier State for β Thalassemia
• Are various heterogenous beta
mutations that produce only small
decrease in production of beta chains.
• Patients have nearly normal beta/alpha
chain ratio and no hematologic
abnormalities.
• Have normal levels of Hb A2.
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9. Beta Thalassemia Minor
• Caused by heterogenous mutations that affect
beta globin synthesis.
• Usually presents as mild, asymptomatic
hemolytic anemia unless patient in under
stress such as pregnancy, infection, or folic acid
deficiency.
• Have one normal beta gene and one mutated
beta gene.
• Hemoglobin level in 10-13 g/dL range with
normal or slightly elevated RBC count.
10. Beta Thalassemia Minor
• Anemia usually hypochromic and
microcytic with slight aniso and poik,
including target cells and elliptocytes; May
see basophilic stippling.
• Rarely see hepatomegaly or splenomegaly.
• Have high Hb A2 levels (3.5-8.0%) and
normal to slightly elevated Hb F levels.
• Are different variations of this form
depending upon which gene has mutated.
• Normally require no treatment.
11. Beta Thalassemia Intermedia
• Patients able to maintain minimum hemoglobin
(7 g/dL or greater) without transfusions.
• Expression of disorder falls between
thalassemia minor and thalassemia major. May
be either heterozygous for mutations causing
mild decrease in beta chain production, or may
be homozygous causing a more serious
reduction in beta chain production.
• See increase in both Hb A2 production and Hb F
production.
• Peripheral blood smear picture similar to
thalassemia minor.
12. Beta Thalassemia Intermedia
• Have varying symptoms of anemia, jaundice,
splenomegaly and hepatomegaly.
• Have significant increase in bilirubin levels.
• Anemia usually becomes worse with infections,
pregnancy, or folic acid deficiencies.
• May become transfusion dependent as adults.
• Tend to develop iron overloads as result of
increased gastrointestinal absorption.
• Usually survive into adulthood.
13. Beta Thalassemia Major
• Characterized by severe microcytic, hypochromic
anemia.
• Detected early in childhood:
– Infants fail to thrive.
– Have pallor, variable degree of jaundice, abdominal
enlargement, and hepatosplenomegaly.
• Hemoglobin level between 4 and 8 gm/dL.
• Severe anemia causes marked bone changes due
to expansion of marrow space for increased
erythropoiesis.
• See characteristic changes in skull, long bones,
and hand bones.
14. Beta Thalassemia Major
• Have protrusion upper teeth and Mongoloid
facial features.
• Physical growth and development delayed.
• Peripheral blood shows markedly hypochromic,
microcytic erythrocytes with extreme
poikilocytosis, such as target cells, teardrop cells
and elliptocytes. See marked basophilic stippling
and numerous NRBCs.
• MCV in range of 50 to 60 fL.
• Low retic count seen (2-8%).
• Most of hemoglobin present is Hb F with slight
increase in Hb A2.
15. Beta Thalassemia Major
• Regular transfusions usually begin around one
year of age and continue throughout life.
• Excessive number of transfusions results in
tranfusional hemosiderosis; Without iron
chelation, patient develops cardiac disease.
• Danger in continuous tranfusion therapy:
– Development of iron overload.
– Development of alloimmunization (developing
antibodies to transfused RBCs).
– Risk of transfusion-transmitted diseases.
• Bone marrow transplants may be future
treatment, along with genetic engineering and
new drug therapies.
16. Comparison of Beta Thalassemias
GENOTYPE HGB A HGB A2 HGB F
NORMAL Normal Normal Normal
SILENT
CARRIER
Normal Normal Normal
MINOR Dec Normal to
Inc
Normal to
Inc
INTERMEDIA Dec Normal to
Inc
Usually Inc
MAJOR Dec Usually Inc Usually Inc
17. Other Thalassemias Caused by Defects in
the Beta-Cluster Genes
• 1. Delta Beta Thalassemia
• 2. Hemoglobin Lepore
• 3. Hereditary Persistence of
Fetal Hemoglobin (HPFH)
18. Delta Beta Thalassemia
• Group of disorders due either to a gene
deletion that removes or inactivates only
delta and beta genes so that only alpha
and gamma chains produced.
• Similar to beta thalassemia minor.
• Growth and development nearly
normal. Splenomegaly
modest. Peripheral blood picture
resembles beta thalassemia.
19. Hemoglobin Lepore
• Rare class of delta beta thalassemia.
• Caused by gene crossovers between
delta locus on one chromosome and
beta locus on second chromosome.
20. Hereditary Persistence of Fetal Hemoglobin
(HPFH)
• Rare condition characterized by continued
synthesis of Hemoglobin F in adult life.
• Do not have usual clinical symptoms of
thalassemia.
• Little significance except when combined
with other forms of thalassemia or
hemoglobinopathies.
• If combined with sickle cell anemia,
produces milder form of disease due to
presence of Hb F.
21. Beta Thalassemia with Hbg S
• Inherit gene for Hb S from one parent and gene
for Hb A with beta thalassemia from second
parent.
• Great variety in clinical severity. Usually
depend upon severity of thalassemia
inherited. Production of Hb A ranges from
none produced to varying amounts. If no Hb A
produced, see true sickle cell symptoms. If
some Hb A produced, have lessening of sickle
cell anemia symptoms.
22. Beta Thalassemia with Hgb C
• Shows great variability in clinical
and hematologic symptoms.
• Symptoms directly related to
which type thalassemia inherited.
• Usually asymptomatic anemia
23. Beta Thalassemia with Hgb E
• Is unusual because results in more
severe disorder than homozygous E
disease.
• Very severe anemia developing in
childhood.
• Transfusion therapy required.
25. Alpha Thalassemia
• Has wide range clinical expressions.
• Is difficult to classify alpha thalassemias due to
wide variety of possible genetic combinations.
• Absence of alpha chains will result in increase
of gamma chains during fetal life and excess
beta chains later in life; Causes molecules like
Bart's Hemoglobin (γ4) or Hemoglobin H (β4),
which are stable molecules but physiologically
useless.
26. Alpha Thalassemia
• Predominant cause of alpha thalassemias is
large number of gene deletions in the alpha-
globin gene.
• Are four clinical syndromes present in alpha
thalassemia:
– Silent Carrier State
– Alpha Thalassemia Trait (Alpha Thalassemia
Minor)
– Hemoglobin H Disease
– Bart's Hydrops Fetalis Syndrome
27. Silent Carrier State
• Deletion of one alpha gene, leaving three
functional alpha genes.
• Alpha/Beta chain ratio nearly normal.
• No hematologic abnormalities present.
• No reliable way to diagnose silent carriers
by hematologic methods; Must be done
by genetic mapping.
• May see borderline low MCV (78-80fL).
28. Alpha Thalassemia Trait
(Alpha Thalassemia Minor)
• Also called Alpha Thalassemia Minor.
• Caused by two missing alpha genes. May
be homozygous (-a/-a) or heterozygous (--
/aa).
• Exhibits mild microcytic, hypochromic
anemia.
• MCV between 70-75 fL.
• May be confused with iron deficiency
anemia.
29. Hemoglobin H Disease
• Second most severe form alpha thalassemia.
• Usually caused by presence of only one gene
producing alpha chains (--/-a).
• Results in accumulation of excess unpaired
gamma or beta chains. Born with 10-40% Bart's
hemoglobin (γ4). Gradually replaced with
Hemoglobin H (β4). In adult, have about 30-50%
Hb H.
γ4 β4
30. Hemoglobin H Disease
• Live normal life; however, infections,
pregnancy, exposure to oxidative drugs may
trigger hemolytic crisis.
• RBCs are microcytic, hypochromic with marked
poikilocytosis. Numerous target cells.
• Hb H vulnerable to oxidation. Gradually
precipitate in vivo to form Heinz-like bodies of
denatured hemoglobin. Cells been described
has having "golf ball" appearance, especially
when stained with brilliant cresyl blue.
31. Bart’s Hydrops Fetalis Syndrome
• Most severe form. Incompatible with life. Have no
functioning alpha chain genes (--/--).
• Baby born with hydrops fetalis, which is edema and
ascites caused by accumulation serous fluid in fetal
tissues as result of severe anemia. Also see
hepatosplenomegaly and cardiomegaly.
• Predominant hemoglobin is Hemoglobin Bart, along with
Hemoglobin Portland and traces of Hemoglobin H.
• Hemoglobin Bart's has high oxygen affinity so cannot
carry oxygen to tissues. Fetus dies in utero or shortly
after birth. At birth, see severe hypochromic, microcytic
anemia with numerous NRBCs.
• Pregnancies dangerous to mother. Increased risk of
toxemia and severe postpartum hemorrhage.
32. Comparison of Alpha Thalassemias
Genotype Hb A Hb Bart Hb H
Normal 97-98% 0 0
Silent Carrier 96-98% 0-2% 0
Alpha Thalassemia
Trait
85-95% 5-10% 0
Hemoglobin H
Disease
Dec 25-40% 2-40%
Hydrops Fetalis 0 80% (with 20%
Hgb Portland)
0-20%
33. Alpha Thalassemia with Hgb S
• Alpha thalassemia can occur in
combination with hemoglobin S. Is
fairly common combination in
populations of African descent.
• Patient usually asymptomatic. Have
less Hb S present than those with
sickle cell trait. Have increased
presence of Hb F.
35. Laboratory Diagnosis of Thalassemia
• Need to start with patient's individual
history and family history. Ethnic
background important.
• Perform physical examination:
–Pallor indicating anemia.
–Jaundice indicating hemolysis.
–Splenomegaly due to pooling of abnormal
cells.
–Skeletal deformity, especially in beta
thalassemia major.
36. CBC with Differential
• Decrease in hemoglobin, hematocrit, mean
corpuscular volume (MCV), and mean
corpuscular hemoglobin (MCH). See normal to
slightly decreased Mean Corpuscular
Hemoglobin Concentration (MCHC). Will see
microcytic, hypochromic pattern.
• Have normal or elevated RBC count with a
normal red cell volume distribution (RDW).
• Decrease in MCV very noticeable when
compared to decrease in Hb and Hct.
37. CBC with Differential
• Elevated RBC count with markedly
decreased MCV differentiates thalassemia
from iron deficiency anemia.
• On differential, see microcytic,
hypochromic RBCs (except in carrier
states). See mild to moderate
poikilocytosis. In more severe cases, see
marked number of target cells and
elliptocytes. Will see polychromasia,
basophilic stippling, and NRBCs.
39. Osmotic Fragility
• Have decreased osmotic fragility.
• Is not very useful fact for
diagnosing thalassemia. Is an
inexpensive way of screening for
carrier states.
40. Brilliant Cresyl Blue Stain
• Incubation with brilliant cresyl blue
stain causes Hemoglobin H to
precipitate. Results in characteristic
appearance of multiple discrete
inclusions -golf ball appearance of
RBCs. Inclusions smaller than Heinz
bodies and are evenly distributed
throughout cell.
41. Acid Elution Stain
• Based on Kleihauer-Betke procedure. Acid
pH will dissolve Hemoglobin A from red
cells. Hemoglobin F is resistant to
denaturation and remains in cell. Stain
slide with eosin. Normal adult cells appear
as "ghost" cells while cells with Hb F stain
varying shades of pink.
• Useful way to differentiate between
pancellular HPFH and heterocellular HPFH.
42. Hemoglobin Electrophoresis
• Important role in diagnosing and differentiating
various forms of thalassemias.
• Can differentiate among Hb A, Hb A2, and Hb F,
as well as detect presence of abnormal
hemoglobins such as Hemoglobin Lepore,
hemoglobin Bart's, or Hemoglobin Constant
Spring.
• Also aids in detecting combinations of
thalassemia and hemoglobinopathies.
43. Hemoglobin Quantitation
• Elevation of Hb A2 excellent way to
detect heterozygote carrier of beta
thalassemia. Variations in gene
expression in thalassemias results in
different amounts of Hb A2 being
produced.
• Can also quantitate levels of Hb F.
44. Routine Chemistry Tests
• Indirect bilirubin elevated in
thalassemia major and intermedia.
• Assessment of iron status, total iron
binding capacity, and ferritin level
important in differentiating
thalassemia from iron deficiency
anemia.
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45. Other Special Procedures
• Globin Chain Testing - determines
ratio of globin chains being
produced.
• DNA Analysis - Determine specific
defect at molecular DNA level.
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46. Differential Diagnosis of Microcytic,
Hypochromic Anemias
RDW Serum
Iron
TIBC Serum
Ferritin
FEP
Iron Deficiency Inc Dec Inc Dec Inc
Alpha Thal Norm Norm Norm Norm Norm
Beta Thal Norm Norm Norm Norm Norm
Hgb E Disease Norm Norm Norm Norm Norm
Anemia of
Chronic Disease
Norm Dec Dec Inc Inc
Sideroblastic
Anemia
Inc Inc Norm Inc Dec
Lead Poisoning Norm Norm Norm Norm Inc
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