THALASSEMIA Flashcards
▪ results of impaired (deficient) globin chain synthesis
THALASSEMIA
▪ may affect either the alpha or beta chain synthesis
THALASSEMIA
THALASSEMIA ▪ diverse group of genetic disorders due to:
a. quantitative reduction in globin chain synthesis for hemoglobin
b. formation of structurally abnormal hemoglobins formed from normal globin chains or parts of normal chains
a. quantitative reduction in globin chain synthesis for hemoglobin
• alpha (a)
• beta (ß)
• gamma (y)
• delta (δ)
b. formation of structurally abnormal hemoglobins formed from normal globin chains or parts of normal chains
• Hb H (ß4)
• Hb Barts (y4)
• Hb Lepore
• Hb Constant Spring (presents with a thalassemic clinical picture)
▪ decreased or non-existent production of one or more globin chain type
THALASSEMIA
• most common thalassemias:
- α-thalassemia: ↓ α-chain(s)
- ß-thalassemia: ↓ ß-chain(s)
▪ human hemoglobin may contain any of seven different globin polypeptide chains
- alpha (α)
- beta (ß)
- G gamma (G γ)
- A gamma (A γ)
- delta (δ)
- epsilon (ɛ)
- zeta (ζ)
▪ globin rearrangement usually occurs in:
• chromosome 11
• chromosome 16
• chromosome 11:
- beta (ß)
- gamma (γ)
• chromosome 16:
- alpha (α)
- zeta (ζ)
- gamma (γ): two types of y chains produced (differ in the 136th position)
- G gamma (Gγ)
- A gamma (Aγ)
- amino acid: glycine
- G gamma (Gγ)
- amino acid: alanine
- A gamma (Aγ)
- delta (δ) - epsilon (ɛ)
- A gamma (Aγ)
141
alpha
zeta
unknown
theta
146
beta
delta
gamma
epsilon
4; Ch 16
alpha
2; Ch 11
beta
delta
gamma
epsilon
2; Ch 16
zeta
double
alpha
gamma
single
beta
delta
epsilon
zeta
: embryonic chains
*Epsilon and zeta
: embryonic counterpart of alpha
*Zeta
: embryonic counterpart of beta, delta, and gamma
*Epsilon
▪ 1 globin
GLOBIN STRUCTURE
▪ protein portion composed of 2 sets (dimer) of 2 different polypeptide chains
GLOBIN STRUCTURE
▪ determines the type of hemoglobin
GLOBIN STRUCTURE
2 ζ 2 ɛ
Gower I
embryonic Hbs
Gower I
Gower II
Portland 2
2 α 2 ɛ
Gower II
ζ 2 γ
Portland 2
2 α 2 γ
Fetal (Hb F)
2 α 2 ß
major Hb A1
A2 2 α 2 δ
minor Hb
newborns and adults
Fetal (Hb F)
major Hb A1
minor Hb A2
Hemoglobin concentrations in adults
major Hb A1: 92-95%
Hb A2: 2-3%
Hb F: 1-2%
• most potential Hb incorporated on RBCs to transport oxygen to the tissues
major Hb A1: 92-95%
• compensation in cases of abnormalities affecting Hb A1
Hb A2: 2-3%
▪ [?] anemia
microcytic and hypochromic
▪ RBC count:
elevated (↑)
▪ abnormalities:
• nucleated RBCs
• microcytosis
• hypochromia
• anisocytosis
• poikilocytosis
• polychromasia
• basophilic stippling
• target cells (predominant)
• leukocytes and platelets
- variations in the shades of cell colors
• polychromasia
- caused by a combination of the affinity of hemoglobin ribosomal RNA
• polychromasia
(predominant)
• target cells
: not affected- display of diffused bluish-gray tint of RBCs
• leukocytes and platelets
▪ concurrent iron deficiency in thalassemia causes:
• lower concentrations of Hb A2 and Hb H
• lower serum iron and iron stores
- may mask diagnosis of heterozygous ß thalassemia and Hb H disease, respectively
• lower concentrations of Hb A2 and Hb H
- Hb H inclusions may be more difficult to detect in red cells
• lower concentrations of Hb A2 and Hb H
▪ diagnosis: in cases of iron deficient individuals, [?] should first be repleted before performing diagnostic tests for thalassemia
iron deficient iron stores
▪ on the short arm of chromosome 16
- ALPHA GENES
: 4 genes (2 genes each inherited from parents)
▪ (αα/αα)
• 2 copies of α-globin gene per chromatid =
4 genes per diploid cell (αα/αα)
▪ nomenclature:
• 1 gene deletion: -α
• 2 gene deletion: (–)
• 3 gene deletion: –/-α or α-/–
• 4 gene deletion: –/– • non-functional α-genes: present but nonfunctional hence do not code for globin synthesis (partially suppressed gene)
• 1 gene deletion:
-α
• 2 gene deletion:
(–)
• 3 gene deletion:
–/-α or α-/–
• 4 gene deletion:
–/–
: present but nonfunctional hence do not code for globin synthesis (partially suppressed gene)
• non-functional α-genes
• non-functional α-genes:
- superscript (+ )
- example: αα+
: -α - α-thalassemia 2 or α+ thalassemia
• 1 gene deletion
- αα/-α or α-/αα
• 1 gene deletion
: (–) - α-thalassemia 1 or αo thalassemia
• 2 gene deletion
- homozygous:
αα/– or –/αα
- heterozygous (1 α-gene deleted per parent):
α-/α- or -α/-α
▪ deficiency in the synthesis of alpha-globin chains
ALPHA THALASSEMIA
▪ each individual has two sets of two alpha genes
ALPHA THALASSEMIA
▪ usual mechanism of suppression: gene deletion
ALPHA THALASSEMIA
• causes suppression of all four genes leading to complete suppression of alpha chain synthesis
gene deletion
• 2 haplotypes:
- one gene deletion: α-thalassemia 2 or α+ thalassemia
- double gene deletion: αthalassemia 1 or αo thalassemia (more severe)
: α-thalassemia 2 or α+ thalassemia
- one gene deletion
: αthalassemia 1 or αo thalassemia (more severe)
- double gene deletion
Alpha Thalassemia Variants
- Silent carrier/α-Thalassemia minor
- α-Thalassemia trait/α-Thalassemia minor
- Hb H Disease
- Bart’s Hydrops fetalis (Hb Barts)
▪ 1/4 α-gene deleted
- Silent carrier/α-Thalassemia minor
▪ heterozygous: α-/αα (α+ )
- Silent carrier/α-Thalassemia minor
▪ remaining 3 α-genes are still able to regulate the synthesis of normal amounts of α-chains
- Silent carrier/α-Thalassemia minor
▪ no signs and symptoms observed
- Silent carrier/α-Thalassemia minor
▪ 2/4 α-genes deleted
- α-Thalassemia trait/α-Thalassemia minor
- α-Thalassemia trait/α-Thalassemia minor
▪ genotypes:
• homozygous: αα/– or –/αα
• heterozygous: α-/α- (1 gene deleted per parent)
▪ can still synthesize α-chains but insufficient
- α-Thalassemia trait/α-Thalassemia minor
▪ MILD signs and symptoms
- α-Thalassemia trait/α-Thalassemia minor
▪ 3/4 α-genes deleted
- Hb H Disease
• α 0 / α+ (–/-a)
- Hb H Disease
▪ remaining 1 gene is unable to dictate the synthesis of the required concentration of α-chain
- Hb H Disease
▪ ↓ α-chain = ↑ ß-chain → tetramer ß4 of hemoglobin
- Hb H Disease
• 1 Hb consists of 4 ß-chains
▪ Hb H
• unstable
▪ Hb H
• leads to formation of Heinz bodies which makes RBCs become rigid and destroyed by spleen
▪ Hb H
: supravitally stained with brilliant cresyl blue (BCB)
Heinz bodies
• phenotype similar to Hb H disease
▪ Hb H-Constant Spring Disease (Hb H/CS)
- inheritance of Hb CS causes a deficit in normal α chains, and when it is inherited along with a double a-gene deletion, it produces a disorder similar to Hb H disease
▪ Hb H-Constant Spring Disease (Hb H/CS)
• caused by compound heterozygous inheritance of Hb Constant Spring (Hb CS) and α 0 thalassemia (–/α CSα)
▪ Hb H-Constant Spring Disease (Hb H/CS)
• more severe hemolysis than in the typical threeα gene deletion Hb H disease
▪ Hb H-Constant Spring Disease (Hb H/CS)
▪ 4/4 α-genes deleted (–/–) (α0 )
- Bart’s Hydrops fetalis (Hb Barts)
▪ no synthesis of α-chains resulting in the production of Hb Barts (tetramer γ4)
- Bart’s Hydrops fetalis (Hb Barts)
: x α-chains
• Hb F
↑ γ-chains
• Hb F
: has a high affinity for oxygen and thus will not effectively release it to the tissues (no oxygen delivered)
• Hb Barts
- suffers still-birth
• fetus
- does not survive (dies inside the uterus)
• fetus:
: swollen (enlarged) head
- hydrops fetalis
▪ can be manifested in as early as the fetal life
- Bart’s Hydrops fetalis (Hb Barts)
• no synthesis of Hb A and Hb F
- Bart’s Hydrops fetalis (Hb Barts)
Classifications of Alpha Thalassemia
One-gene deletion (αα/α)
Two gene deletion (-α/α; αα/–)
Three-gene deletion (-α/-)
Silent Carrier/ α-Thal minor
One-gene deletion (αα/α)
▪ hematology: normal with few target cells and elliptocyte
One-gene deletion (αα/α)
▪ asymptomatic
One-gene deletion (αα/α)
Two gene deletion (-α/α; αα/–)
AlphaThalasse mia Trait/ αThal minor
Two gene deletion (-α/α; αα/–)
▪ mild anemia
Two gene deletion (-α/α; αα/–)
▪ microcytic hypochromic
Two gene deletion (-α/α; αα/–)
Three-gene deletion (-α/-)
▪ elliptocytes
Two gene deletion (-α/α; αα/–)
▪ target cells
Two gene deletion (-α/α; αα/–)
▪ Hb A (60%)
Two gene deletion (-α/α; αα/–)
▪ Hb Barts (5- 10%)
Two gene deletion (-α/α; αα/–)
Hb H Disease
Three-gene deletion (-α/-)
▪ Hb H inclusions (Heinz bodies)
Three-gene deletion (-α/-)
▪ high retics
Three-gene deletion (-α/-)
▪ 30% Hb H (ß4) – precipitated into Heinz bodies
Three-gene deletion (-α/-)
▪ Constant Spring disease (Hb H/CS)
Three-gene deletion (-α/-)
– precipitated into Heinz bodies
▪ 30% Hb H (ß4)
• 6% Hb Barts
α-Thal minor (one & two gene deletion)
- asymptomatic (accidentally discovered) in adults (not diagnostic)
α-Thal minor (one & two gene deletion)
- considered diagnostic in newborns
α-Thal minor (one & two gene deletion)
▪ short arm of chromosome 11
- BETA GENES
▪ one copy per chromatid
- BETA GENES
• total: 2 ß-genes per diploid cell
- BETA GENES
• ß/ß
- BETA GENES
: gene cannot fully synthesize required number of ß-chains (decreased production but not fully deficit)
▪ + superscript (+ )
: deleted gene (no production)
▪ 0 superscript (0 )
: reduced ß-chain production
▪ ß +
: no ß-chain production
▪ ß 0
: δ and ß-gene deletion
▪ (δß)0
: Hb Lepore designation
▪ (δß)Lepore
• nonhomologous meiotic crossing over between δ and ß globin genes (exchanging of genetic material or traits) on chromosome 11
▪ (δß)Lepore
▪ unbalanced globin chain synthesis due to a lack of, or to the reduced production of, ß chains
BETA THALASSEMIA
• causes an excess of α chains (very unstable)
BETA THALASSEMIA
- normally, production of α and ß chains should be proportionate (equal production for them to be paired – Hb A1)
BETA THALASSEMIA
BETA THALASSEMIA
• minor imbalance:
unpaired α chains are simply removed by proteolysis during erythroid maturation
BETA THALASSEMIA
• major imbalance:
overwhelmed/massive number of unpaired α chains (excess free α chains) precipitate (results to Heinz bodies), causing severe erythrocyte dysfunction (rigid RBCs)
- defective red cells are destroyed by bone marrow macrophages causing ineffective erythropoiesis and a massively enlarged erythron
BETA THALASSEMIA
▪ characterized by a deficiency in Beta-globin chain synthesis
BETA THALASSEMIA
▪ each individual has one set of two beta genes
BETA THALASSEMIA
▪ suppression or absence of these beta genes results to deficient beta chain synthesis
BETA THALASSEMIA
Classifications of Beta Thalassemia
ß-Thal Minor/Trait (Cooley’s Trait)
ß-Thal Intermedia
ß-Thal Major (Cooley’s Anemia)
ß 0 /ß0
ß-Thal Major (Cooley’s Anemia)
severe
ß-Thal Major (Cooley’s Anemia)
ß/ß+ or ß/ß0
ß-Thal Minor/Trait (Cooley’s Trait)
silent
ß-Thal Minor/Trait (Cooley’s Trait)
ß + /ß+ or ß+ /ß0
ß-Thal Intermedia
moderate
ß -Thal Intermedia
▪ 1/2 normal ß-gene: still able to synthesize at least enough ß-chains
ß-Thalassemia Minor/Cooley’s Trait (ßO /ß)
• other ß-gene: either deleted or suppressed
ß-Thalassemia Minor/Cooley’s Trait (ßO /ß)
▪ still able to produce sufficient quantities of HbA1
ß-Thalassemia Minor/Cooley’s Trait (ßO /ß)
▪ hemoglobin levels: slightly low
ß-Thalassemia Minor/Cooley’s Trait (ßO /ß)
ß-Thalassemia Minor/Cooley’s Trait (ßO /ß)
▪ blood smear:
• shows similar morphology as in Thalassemia Major or Intermedia
• mild microcytic-hypochromic anemia
• basophilic stippling
• target cells
ß-Thalassemia Minor/Cooley’s Trait (ßO /ß)
▪ Hb F level:
▪ Hb A2 level:
▪ Hb A1 level:
▪ Hb F level: 2-3%
▪ Hb A2 level: elevated
▪ Hb A1 level: decreased
▪ caused by a partial suppression of the Beta genes
ß-Thalassemia Intermedia (ß+ /ß+ )
▪ lesser production of Hb A1
ß-Thalassemia Intermedia (ß+ /ß+ )
▪ symptoms are similar with that of Beta Thalassemia major, but depend on the extent of gene suppression
ß-Thalassemia Intermedia (ß+ /ß+ )
▪ milder than Beta Thalassemia major
ß-Thalassemia Intermedia (ß+ /ß+ )
ß-Thalassemia Intermedia (ß+ /ß+ )
▪ genotypes:
• homozygous: ß + /ß+
• heterozygous: ß + /ß0
▪ complete lack of Beta globin production
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
• markedly decreased or absence of ßchain synthesis (resulting in excess α chains)→ no production of Hb A1
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
-[?]Hb F becomes increased up to [?] to compensate for the absence of Hb A1
1-3%
40-60%
- Hb F can go as high as [?]
90-98%
▪ most affected patients exhibit retarded growth with mongoloid facial features and severe anemia
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
▪ marked by characteristic changes in RBC morphology:
• microcytosis
• hypochromia
• anisocytosis
• poikilocytosis
• increased nucleated RBCs
• basophilic stippling
• Pappenheimer bodies
• Heinz bodies (resulted from precipitated unpaired α chains)
• numerous target cells, Howell-Jolly bodies, and siderocytes
• ↑serum iron and bilirubin
▪ HbF level: 40-60% (elevated)
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
▪ requires repeated/continuous blood transfusion
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
▪ Hb Lepore:
(δß)Lepore/(δß)Lepore
• composed of two normal α chains and two abnormal nonα chains formed by fusion of the N-terminal end of a δ chain and the C-terminal end of a ß chain
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
• caused by nonhomologous meiotic crossing over between the δ and ß globin gene loci
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
• remaining portions of the δ and ß genes form an antiLepore gene (to stop all portions in becoming abnormal)
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
• chromosome bearing the Lepore δß fusion gene lacks intact δ and ß genes
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )
• 3 different Lepore hemoglobins: each differs in the point at which crossing over occurs
- Hb Lepore-Baltimore
- Hb Lepore-Boston (most common)
- Hb Lepore-Hollandia
• all Hbs Lepore are ineffectively synthesized, causing a ß thalassemia syndrome
ß-Thalassemia Major/Cooley’s Anemia (ßO /ßO )