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Chapter 12
Thalassemia
1
Thalassemia
► In
Chapter 12, 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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Introduction to
Thalassemia
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Thalassemia
1 of 2
► 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.
► Globin chains structurally normal (is how
differentiated from hemoglobinopathy), but have
imbalance in production of two different types of
chains.
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Thalassemia
2 of 2
► 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 malaria.
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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.
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Beta
Thalassemia
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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 transfusiondependent hemolytic anemia.
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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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Beta Thalassemia Minor
1 of 2
► 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.
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Beta Thalassemia Minor
2 of 2
► 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.
► Make sure are not diagnosed with iron deficiency
anemia.
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Beta Thalassemia Intermedia
1 of 2
► 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.
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Beta Thalassemia Intermedia
2 of 2
► 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.
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Beta Thalassemia Major
► Characterized
1 of 3
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.
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Beta Thalassemia Major
2 of 3
► 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.
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Beta Thalassemia Major
3 of 3
► 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.
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Comparison of Beta Thalassemias
GENOTYPE
HGB A
HGB A2
HGB F
NORMAL
Normal
Normal
Normal
SILENT
CARRIER
Normal
Normal
Normal
MINOR
Dec
INTERMEDIA
Dec
Normal to
Inc
Usually Inc
MAJOR
Dec
Normal to
Inc
Normal to
Inc
Usually Inc
Usually Inc
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Other Thalassemias Caused by
Defects in the Beta-Cluster Genes
► 1.
Delta Beta Thalassemia
► 2. Hemoglobin Lepore
► 3. Hereditary Persistence of Fetal
Hemoglobin (HPFH)
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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.
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Hemoglobin Lepore
► Rare
class of delta beta thalassemia.
► Caused by gene crossovers between delta
locus on one chromosome and beta locus
on second chromosome.
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Hereditary Persistence of Fetal
Hemoglobin (HPFH) 1 of 2
► 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.
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Hereditary Persistence of Fetal
Hemoglobin (HPFH) 2 of 2
► Hb
F more resistant to denaturation than Hb
A. Can be demonstrated on blood smears
using Kleihauer Betke stain. Cells
containing Hb F stain.
► Classified into two groups according to
distribution of Hb F among red cells:
 Pancellular HPFH - Hemoglobin F uniformly
distributed throughout red cells.
 Heterocellular HPFH - Hemoglobin F found in
only small number of cells.
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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.
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Beta Thalassemia with Hgb C
► Shows
great variability in clinical and
hematologic symptoms.
► Symptoms directly related to which type
thalassemia inherited.
► Usually asymptomatic anemia
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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.
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Alpha
Thalassemia
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Alpha Thalassemia
1 of 2
► 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.
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Alpha Thalassemia
2 of 2
► 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
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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).
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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.
► Although some Bart's hemoglobin (γ4) present at
birth, no Bart's hemoglobin present in adults.
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Hemoglobin H Disease
1 of 2
► 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
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Hemoglobin H Disease
1 of 2
► 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.
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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.
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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
Dec
25-40%
2-40%
0
80% (with 20%
Hgb Portland)
0-20%
Hemoglobin H
Disease
Hydrops Fetalis
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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.
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Laboratory
Diagnosis of
Thalassemia
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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.
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CBC with Differential
► See
1 of 2
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.
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CBC with Differential
2 of 2
► 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.
40
Reticulocyte Count
► Usually
elevated. Degree of elevation
depends upon severity of thalassemia.
41
Osmotic Fragility
► Have
decreased osmotic fragility.
► Is not very useful fact for diagnosing
thalassemia. Is an inexpensive way of
screening for carrier states.
42
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.
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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.
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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.
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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.
46
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.
47
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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Differential Diagnosis of Microcytic,
Hypochromic Anemias
RDW
Serum
Iron
TIBC
Serum
Ferritin
FEP
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
Inc
Inc
Norm
Inc
Dec
Norm
Norm
Norm
Norm
Inc
Iron Deficiency
Sideroblastic
Anemia
Lead Poisoning
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