Anemia:- Part 4 – Thalassemia, α-thalassemia and β-thalassemia, Workup and Diagnosis

Thalassemia

What sample is needed for Thalassemia?

1. Venous blood is needed.
2. Prepare a fresh peripheral blood smear.

How will you define thalassemia?

1. Thalassemia is an inherited hemoglobinopathy resulting from the decreased production rate of one or more globin chains of hemoglobin. Or
2. These are a heterogeneous group of genetic disorders resulting from the decreased synthesis of α or β chains of hemoglobin.

What will be the result of decreased hemoglobin synthesis?

1. Decreased hemoglobin in the RBCs.
2. Hypochromasia.
3. Microcytosis.
4. Variable degree of hemolysis.
5. Also called Cooley’s anemia.

What is the history of Thalassemia?

1. Thalassemia derives from combining the Greek words Thalassa, meaning sea, and Haima, meaning blood.
2. This was known as Mediterranean anemia because it is the most common occurrence in the Mediterranean population.
3. This is characterized by a decreased production rate of globin chains, which are classified according to the globin involved.
4. The consequence is defective globin chain production.

What is the structure of hemoglobin?

1. The normal globin, part of the hemoglobin, consists of 2 alpha and 2 beta chains.

Hemoglobin (Hb) normal structure

What are the various types of hemoglobin and their structures?

2. Each pair is inherited from each parent.
   1. So one α/β gene is inherited from the father and the other α/β pair from the mother.

Hemoglobin (Hb) gene location

3. In thalassemia, a gene may involve either α or β chains.
4. In the majority of the patients, the β-chain is involved.
5. HbA1 has 2 α and 2 β-chains.
6. HbA2 has 2 α and 2 δ-chains.
7. HbF has 2 α and  2 γ-chains.
8. All these hemoglobins, HbA1, HbA2, and HbF, are present in the adult RBCs.
9. HbA2 and HbF are present in trace amounts.

What is the genetic code of Thalassemia?

1. The genes located on chromosome 11 are γ, δ, ε, and β-chains.
2. While on chromosome 16, there are 2 α and ζ loci.
3. β-thalassemia:
   1. Only one of the β-chains is involved in heterozygous conditions, called β-thalassemia minor.
   2. In homozygous conditions, both β-chains are involved, called β-thalassemia major.
4. α-thalassemia:
   1. α-chain involvement is more complicated.
   2. Because there are 2 α-gene loci on chromosome 16, while the β-gene is only one locus on chromosome 11.
   3. In silent carriers of α-thalassemia, only one of the 4 α-genes (1/4) is absent (deleted or abnormal).
   4. In α-thalassemia minor, 2 of the 4 α-genes (2/4) are affected. There may be a deletion or an abnormality in both gene loci.
   5. In α-thalassemia-1, which is more common in Asians.
   6. In α-thalassemia-2, which is more common in Africans and Mediterranean people.
5. HbH disease occurs because of the deletion or inactivation of the three gene loci (3/4). Thus, all four globin chains are β-chains.
6. Hemoglobin Bart’s disease is more serious when all 4 α-genes (0/4) are deleted or inactivated. There are all 4 γ-globins.

Hemoglobin gene’s location

What is the mechanism of Thalassemia?

1. Thalassemia syndrome may occur because of the abnormality of the following:
   1. Coding sequence.
   2. Transcription.
2. Processing or defects in gene translation lead to thalassemia.

How will you classify Thalassemia?

• The older classification classifies thalassemia based on the severity of the disease as follows:

Thalassemia major:

1. α-globin genes are absent (0= –/–).
2. Hemoglobin (Hb) Bart’s at birth is 75%.
3. MCV = 110 to 120 fl.
4. MCH is significantly decreased.
5. This is also called hydrops fetalis.
6. What are the signs and symptoms of Thalassemia major?
   1. The complete absence of the α-globin genes in fetal life leads to intrauterine death of the fetus due to severe hypoxemia.
   2. This is due to Hb Bart’s, which has a high affinity for oxygen and prevents the release of O2 to the tissues.
   3. At birth, no S/S.
   4. Infants during 3 to 6 months show pallor, yellow skin, and sclera.
   5. Infants from 6 to 12 months show severe anemia and bone abnormalities and can’t thrive.
   6. There are life-threatening complications.
   7. There is splenomegaly or hepatomegaly.
   8. These patients will have frequent infections.
   9. There is a tendency for bleeding, like a nosebleed.
   10. These patients have a small body, but the large head is a characteristic feature.
   11. These infants may be mentally retarded.

Thalassemia Intermedia:

1.  There is some degree of anemia, jaundice, and splenomegaly.
2. There are signs of hemosiderosis, such as hemoptysis.
3. There is iron deficiency anemia.

Thalassemia minor:

1. One globin gene is absent (-α/αα).
2. These are the silent carriers.
3. There are usually no symptoms.
4. There is mild anemia.
5. MCV is normal to slightly decreased.
6. HbH small amount of 1% to 2% may be present at birth. This will disappear later on.
7. Often, these patients are overlooked.

Thalassemia minima:

1. It is a mild disease.
2. It is a silent carrier of the β-thalassemia trait.
3. Anemia is not evident.
4. HbA2 = normal or slightly increased. HbF is increased.
5. Normal RBC morphology and Hb electrophoresis.

What is the other way to classify Thalassemia?

1. It is based on the genetic makeup of the hemoglobin, and it is divided into:
   1. α-Thalassemia.
   2. β-Thalassemia

Alpha- thalassemia (α-thalassemia)

How will you define Alpha-Thalassemia?

1. α-thalassemia is a group of genetic disorders with defective α-chain synthesis.
2. Chromosome 16 carries 2 α genes, and the total number of α-gene is 4.
3. Severity depends upon the number of genes affected by the patient, one, two, three, or four.
4. Decreased synthesis of α-chain will decrease the synthesis of HbA, HbF, and HbA2 because these chains have α-chains; the net result will be an excess of β-chains and γ-chains. These chains may polymerize into tetrameric forms γ4 called Hb Bart’s and β4 called HbH.
   1. These abnormal Hb Bart’s and HbH are the characteristics of α-thalassemia.

What is the presentation of Alpha-Thalassemia?

1. Usually manifested immediately after birth or even in utero because the α-gene is activated early in fetal life.
2. α-thalassemia has a wide range of clinical presentations.
3. Chromosome 16 carries 2 α genes; the total will be 4 α-genes (each pair from the parents). The severity of the disease will vary depending on the number of genes affected in one patient (one, two, or three genes).
4. Another feature of α-thalassemia is that decreased or absent α-gene production results in more than γ-chain during fetal life and at birth, and an excess of β-chain later on.
5. This will lead to stable tetramers,  γ4 (Hb Bart’s) and β4 (Hb H).  Hemoglobin Bart’s and H precipitate in the older RBCs.
6. These may lead to hemolytic crises by infection. This abnormal hemoglobin can be detected by electrophoresis.

The Alpha-Thalassemia mechanism for hemolytic crises

α-thalassemia minor:

How will you define Alpha-Thalassemia minor?

1. These are silent carriers.
2. There is decreased production of the α-chain (α⁺-α / ββ).
3. One α-globin gene is affected = -α/αα.
4. These are the silent carriers, and there is no marked anemia.
5. MCV will be normal, but may decrease slightly.
6. Hb H (1% to 2%) is present at birth and disappears later.

α-thalassemia trait:

How will you define the Alpha-Thalassemia trait?

1. It has  2 α-globin genes affected = α-/α- or αα/–.
   1. RBCs show microcytosis and hypochromic anemia.
   2. MCV is <70fl.
   3. There is mild anemia.
   4. Serum electrophoresis showed 5% to 10% Hb H (4 β) at birth, which will disappear later.

α-thalassemia major:

How will you define Alpha-Thalassemia major?

1. It is Hb H disease.
2. Three α-globin genes are affected = α-/–.
3. There is microcytic hypochromic anemia.
4. MCV is <70 fl.
5. Serum electrophoresis showed predominantly Hb Bart’s, consisting of 4 gamma chains at birth.
6. There is a gradual shift from HbH 5% to 30% over the first few months of life.

What are the Alpha-thalassemia characteristic features?

What is the α-thalassemia classification and characteristic features?

What are the clinical features of alpha-thalassemia?

1. In case of loss of all 4 α-genes, life is incompatible and leads to the fetus’s death (hydrops fetalis).

Thalassemia showing Hydrops fetalis

2. Microcytic hypochromic anemia with splenomegaly. This is known as Hb H disease because of the presence of Hb H (β4). Can find this Hb on electrophoresis.
3. In fetal life, Hb Bart’s is seen.
4. α-Thalassemia trait is caused by the loss of one or two α-genes that are not usually associated with anemia, but MCV and MCH are low.

Beta-thalassemia (β-thalassemia):

Beta-thalassemia major:

How will you define Beta-Thalassemia?

1. This is also called Cooley’s anemia and is the homozygous state of β-thalassemia
2. It consists of 2 α chains and 2 γ-chains.
3. The production of the β-chain is decreased (α2 / β⁰ β⁰).
4. A globin gene mutation causes partial β-gene or total β-gene chain loss.
5. The number of genes affected, partial or complete, will determine the severity of the disease.
6. The production of γ-chains and δ-chains has increased, resulting in increased Hb F and Hb A2 levels.
7. The β chain is replaced by the 2-γ chain, which will form Hb F; the other is replaced by δ-chains, which will form Hb A2.
8. These are usually homozygous (β⁰β⁰):
9. β⁰β⁰-thalassemia is a more severe variant. No β-chains are synthesized.
10. No Hb A found on electrophoresis.
11. Only HbF (>90%) and HbA2 (3% to 8%) are found.
12. This is also called Cooley’s anemia.
13. There is marked microcytosis and hypochromasia.
14. MCV is <70 fl, and Hb is 2 to 3 g/dL.
15. There is hepatosplenomegaly, bony deformities, and failure to thrive as an infant.
16. These patients are dependent upon blood transfusions.

Thalassemia beta mechanism

Beta – thalassemia minor:

1. Where a single β-gene is affected (β⁰/β).
   1. There is mild anemia, Hb 9 to 11 g/dL, or no anemia.
   2. Normal to increased RBC count.
   3. RBCs are microcytes, MCV 60 to 70 fl.
   4. Electrophoresis shows a mild increase in Hb F and Hb A2 (3% to 8%).

Beta – thalassemia intermedia:

1. It is most commonly caused by partial deletion of β⁰ of both beta genes.
2. These are homozygous (β⁺β+) genes.
3. It will give a wide spectrum of the disease with moderate to severe anemia, and Hb will be 6 to 10 g/dL.
4. There are growth retardation and bony abnormalities.
5. This usually occurs later than the major thalassemia type.
6. Electrophoresis shows Hb F 20% to 40% and increased Hb A2, 3% to 8%.

Thalassemia intermedia on electrophoresis

What is another classification of Beta-Thalassemia?

1. β⁰⁺ shows a complete absence of the production of the beta chains.
   
   1. This is found in the Mediterranean, particularly in northern Italy, Greece, Algeria, Saudi Arabia, and Southeast Asia.
2. β⁺-thalassemia is less severe.
   1. There are three groups of this gene rearrangement.
3. 1β⁺ thalassemia gene produces a smaller amount of the beta-chain, around 10% of normal production.
   1. This group is found throughout the Mediterranean, the Middle East, the Indian subcontinent, and Southeast Asia.
4. The 2β⁺ thalassemia gene produces more beta-chain, around 50% of the normal population.
   1. This is found in the blacks of North America and West Africa.
      
5. The 3β⁺thalassemia gene produces even more beta chains, leading to milder disease.
   1. It is found particularly in Italy, Greece, and the Middle East.
6. Severe thalassemia is called thalassemia major.
   1. Severe hypochromic and microcytic anemia develops during the first year of life.
   2. Hemoglobin is <7 g/dL and consists mostly of HbF and HbA2.
7. Homozygous type 2 and 3 beta⁺ causes a milder form of thalassemia called Thalassemia intermedia.
   1. The heterozygous beta-thalassemia gene causes a milder form of anemia.
      1. This also shows mild hypochromasia and microcytosis, called Thalassemia minor.
   2. The minor group may show a delta-chain abnormality.
8. Beta-delta Thalassemia (δβ)  is another rare form of thalassemia characterized by the combined defect in δ and β chain synthesis.
   1. This group may have a normal level of Hb A2 and usually a high level of Hb F in the heterozygote and absent Hb A and A2 in the homozygote.
9. δβ-thalassemia can be divided into two groups according to the Hb F found:
   1. If the γ-gene is active, then that group is called GγAγδβ thalassemia.
10. Another type that has inactive γ, δ, and β genes is called Gγδβ thalassemia.

What are the findings of Beta-thalassemia syndrome?

What are the clinical features of beta-thalassemia?

1. In beta-thalassemia major, there is severe anemia, which appears 3 to 6 months after birth.
2. The liver and spleen enlargement is due to increased destruction of the RBCs, intramedullary hemopoiesis, and iron overload.
3. Splenomegaly needs more blood and increases RBC destruction and pooling.
4. Bone marrow hyperplasia in thalassemia leads to a thalassemic face. Thinning of the bone cortex may lead to bone fractures.
5. X-rays may show the bossing of the skull and typically a hair-on-end appearance.
6. What are the Lab findings of beta-thalassemia?
   1. Low Hemoglobin.
   2. The peripheral blood smear shows Hypochromic and microcytic anemia.
   3. Hb electrophoresis confirms the diagnosis by the near absence of the decreased level of Hb A.

Hemoglobin (Hb) electrophoresis in Thalassemia

Hemoglobin on electrophoresis is different in different types of thalassemia.

How will you summarize Thalassemia types?

1. α-Thalassemia trait is due to a double gene deletion.
   1. There are microcytes and hypochromasia.
   2. α-Thalassemia disease is due to three gene deletions.
   3. Target cells, ovalocytes, microcytes, and Hb H are included in the RBCs.
2. β-Thalassemia in heterozygotes, and there is a β gene deletion alone or combined with the δ gene.
   1. There are microcytes, target cells, elliptocytes, and basophilic stippling.
3. β-Thalassemia in homozygotes, and there is a β gene deletion alone or in combination with the δ gene.
   1. It is marked as hypochromasia with polychromatic rims.  There are target cells, ovalocytes, basophilic stippling, and HbH crystals.

Beta-Thalassemia blood smear

What is the differential diagnosis of Beta-thalassemia?

How will you treat Thalassemia major?

1. These patients survive by blood transfusion. An attempt is made to maintain hemoglobin levels over 10 g/dL.
   1. It usually requires 2 to 3 units every 4 to 6 weeks.
   2. Fresh blood, filtered to remove white blood cells, gives the best RBC survival and fewer reactions.
   3. 500 mL of blood contains 250 mg of iron.
2. Regularly give the folic acid 5 mg/day.
3. Iron supplements are contraindicated.
4. Iron overload is a complication that needs chelating therapy to control iron overload.
   1. Deferoxamine is the most common drug used for the chelation of iron.
   2. This can be given 1 to 2 mg with each unit of blood.
   3. Give 40 mg/kg subcutaneously over 8 to 12 hours, 5 to 7 days weekly.
   4. This should be started in infants after 10 to 15 units of blood transfusion.
5. Excess iron causes skin pigmentation and damages the heart.
   1. Assessment of the iron status advises:
      1. Serum ferritin.
      2. Serum iron.
      3. % saturation of transferrin.
      4. Serum non-transferrin-bound iron.
6. A bone marrow biopsy of reticuloendothelial stores was done using Perl’s stain.
7. Liver biopsy for parenchymal and reticuloendothelial stores.
   1. Assessment of the tissue damage  caused by the iron overload:
8. For heart damage caused by iron, advice:
   1. X-ray chest.
   2. ECG, 24-hour monitoring.
   3. Echocardiography.
   4. Radionuclide scans to check left ventricular ejection.
9. For liver damage caused by iron, the advice is:
   1. LFT.
   2. Liver biopsy.
   3. CT scan or MRI.
10. For endocrine gland damage caused by iron, advice:
    1. Glucose tolerance test.
    2. Pituitary gonadotropin release test.
    3. Growth hormone assay.
    4. Radiology of the bones.
    5. Isotope bone density study.
    6. Functional tests of the thyroid, parathyroid, adrenal, and gonadal glands.
11. Vitamin C 200 mg/day. This will help in the excretion of iron produced by deferoxamine.
12. Immunization against the Hepatitis B virus.
13. Allogenic bone marrow transplantation will give a permanent cure.
14. Infections are quite common in these patients and need treatment with antibiotics.
15. Treatment for β-thalassemia:
    1. This is supportive treatment.
    2. Antibiotics for infections.
    3. Folic acid supplement.
    4. Transfusion of packed RBCs to raise the hemoglobin.
    5. Splenectomy may be advised.
    6. Bone marrow transplantation may be done.

How to treat Alpha-thalassemia?

1. Blood transfusion.
2. In utero, a blood transfusion is required in case of hydrops fetalis.

How will you screen and diagnose the thalassemia patient?

1. The peripheral blood smear is typical of microcytic and hypochromic anemia.
2. In the case of homozygous β-thalassemia and double heterozygous non-α-thalassemia, the peripheral smear shows:
   1. Severe anisocytosis.
   2. Poikilocytosis with a bizarre shape.
   3. There are target cells.
   4. There are ovalocytes.
   5. There are numerous nucleated RBCs.

Thalassemia (homozygous) blood smear

3. In heterozygous β-thalassemia, peripheral blood smear shows:
   1. There are hypochromic microcytic RBCs with moderate anisocytosis and poikilocytosis.
   2. Basophilic stippling is also seen.
4. MCV is the best screening for patients with thalassemia. There is a decreased MCV, with an 85% chance if this is <75 fl (femtoliters).
5. RBC count of >5 million/mm³.
6. Hemoglobin (Hb) level is <9 g/dL.
7. MCHC <30%.
8. Reticulocytes are increased in these patients. This is increased in:
   1. In Hb-H disease may be up to 10%.
   2. In homozygous β-thalassemia may reach 5%.
9. Normal RDW (red cell volume distribution width).
   1. The only exception to RDW in Thalassemia major is the degree of anisocytosis, leading to an increased level.
   2. In iron deficiency, the RDW is increased, and the decrease in MCV is less striking.

How will you differentiate various anemias?

10. In heterozygous thalassemia, MCH is <22 pg, MCV <70 fl, and Hb is around 9 to 11 g/dL.
11. Cord blood can be used to diagnose thalassemia.
12. DNA analysis of the chorionic villus sample at 8 to 10 weeks of pregnancy.
13. Or Amniotic fluid cells by amniocentesis at 16 to 18 weeks.
14. Serum electrophoresis of the infants.
    1. Electrophoresis plays an important role in diagnosing thalassemia, and it will detect an increased level of HbA2, HbF, and other abnormal hemoglobins (HbH and Bart’s).

What is the picture of β-thalassemia hemoglobin on Hb-electrophoresis?

How will you summarize thalassemia?

Questions and answers: