Anemia – Part 4 – Thalassemia, Discussion and Work Up

December 14, 2020HematologyLab Tests

Thalassemia

History of Thalassemia

1. Thalassemia derives from the combination of the Greek word Thalassa means sea, Haima means blood.
2. This was known as Mediterranean anemia because of the most common occurrence in the Mediterranean population.
3. This is characterized by a decreased rate of production of globin chains.  These are classified according to the globin which is involved.
4. The consequence is defective globin chain production.
5. To understand thalassemia, we need to discuss and understand the structure of the Hemoglobin:
   1. The normal globin, which is part of the hemoglobin, consists of 2 alpha chains and 2 beta chains.
      

      Hemoglobin normal structure

6. Genetic code is located on chromosomes 11, are γ, δ, ε, and β-chains.
   1. While on chromosome 16, there are α and ζ loci.
      

      Globin genes location for hemoglobin formation

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

   Hemoglobin gene locus encoding

   Various types of hemoglobin:

   Type of hemoglobin	Genotype of hemoglobin	Functions of the hemoglobin
   Hb A	α2β2	This is the main adult Hb
   Hb A2	α2/δ2	This is present in a small amount
   Hb F	α2/γ2	Main fetal Hb in late stages
   Hb gower1	ζ2/ε2	This Hb is present in the early life of the fetus
   Hb gower2	α2/ε2	This Hb is present in a small amount in the early fetal life

Classification of the Thalassemia:

Alpha- thalassemia:

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

      Thalassemia alpha mechanism, the formation of Hb Bart’s and Hb H

   4. α-thalassemia minor, there is decreased production of the α-chain (α⁺ -α / ββ).
      1. One α-globin gene is affected = -α/αα.
      2. These are the silent carrier, and there is no marked anemia.
      3. MCV will be normal to decrease slightly.
      4. Hb H (1% to 2%) is present at birth which disappears later on.
   5. α-thalassemia trait, 2 α-globin genes are 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 on.
   6. α-thalassemia major is Hb H disease.
      1. Three α-globin genes are affected = α-/–.
      2. There is microcytic, hypochromic anemia.
      3. MCV is <70 fl.
      4. Serum electrophoresis showed predominantly Hb Bart’s, and this consists of 4 gamma chains at birth.
      5. There is a gradual shift to Hb H 5% to 30% over the first few months of life.

Alpha-thalassemia Characteristic features:

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

Alpha-Thalassemia leading to hydrops fetalis

1. 1. 2. Microcytic hypochromic anemia with splenomegaly. This is known as Hb H disease because of the presence of the Hb H (β4). This Hb can be found 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 are not usually associated with anemia, but MCV and MCH are low.

Beta-thalassemia:

1. 1. Definition:
   2. There is decreased production of the β-chain (α2 / β⁰ β⁰). There is a globin gene mutation that causes partial β-gene or total β-gene chain loss.
   3. The number of genes affected, partial or complete, will determine the severity of the disease.
   4. There is an increase in the production of γ-chains and δ-chains, resulting in an increased level of Hb F and Hb A2.
   5. There is the replacement of the β chain by the 2-γ chain, which will form Hb F, and the other replaced by δ-chains will form Hb A2.
      

      Beta-Thalassemia mechanism and formation of HbF and HbA2

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

         Thalassemia intermedia on electrophoresis

   8. β-thalassemia major are usually homozygous (β⁰β⁰):
      1. β⁰β⁰-thalassemia is a more severe variant. No β-chains are synthesized.
      2. No Hb A found on electrophoresis.
      3. Only HbF (>90%) and HbA2 (3% to 8%) are found.
      4. This is also called Cooley anemia.
      5. There is marked microcytosis and hypochromasia.
      6. MCV is <70 fl and Hb is 2 to 3 g/dL.
      7. There is hepatosplenomegaly, bony deformities, and failure to thrive as an infant.
      8. These patients are dependent upon blood transfusion.
         

         Thalassemia major on electrophoresis

2. Another classification:
   1. β⁰⁺ shows a complete absence of the production of the beta chains.
      
      1. This is found in the Mediterranean area, particularly in Northern Italy, Greece, Algeria, Suadi Arabia. and Southeast Asia.
   2. β⁺-thalassemia is less severe.
      1. There are three groups of this gene rearrangement.
   3. 1β⁺ thalassemia gene produces less amount of the beta-chain around 10% of normal production. This group is found throughout the Mediterranian region, middle east,  Indian subcontinent, and Southeast Asia.
      
   4. 2β⁺ thalassemia gene produces more amount fo the beta-chain around 50% of the normal population. This is found in the blacks of North America and West Africa.
      
   5. 3β⁺thalassemia gene produces even more amount of beta chains and gives rise to milder disease. It is found particularly in Italy, Greece, and the Middle east.
      1. Severe thalassemia is called thalassemia major.
         1. Sever hypochromic, and microcytic anemia develops during the first year of life.
         2. Hemoglobin is <7 g/dL and consists mostly of HbF and HbA2.
      2. Homozygous type 2 and 3 beta⁺ causes a milder form of the 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.
      3. The minor group may show delta-chain abnormality.
3. Beta-delta thalassemia (δβ)  is another occasional 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.
   2. δβ-thalassemia can be divided into two groups according to Hb F found:
      1. If γ-gene is active, then that group is called GγAγδβ thalassemia.
      2. Another type that has inactive γ, δ, and β genes is called Gγδβ thalassemia.

Clinical features of beta-thalassemia:

1. 1. In beta-thalassemia major, there is severe anemia, which appears at 3 to 6 months after birth.
   2. There is an enlargement of the liver and spleen due to increased destruction of the RBCs, intramedullary hemopoiesis, and later on by the iron overload.
   3. Splenomegaly needs more blood and increases RBC destruction and pooling.
   4. Bone marrow hyperplasia in thalassemia leads to thalassemic face. There is thinning of the cortex, which may lead to bone fractures.
   5. X-rays may show the bossing of the skull and typically a hair-on-end appearance.

Lab findings of beta-thalassemia:

1. 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 electrophoresis for Beta-Thalassemia

Hemoglobin on electrophoresis is different in different types of thalassemia.

Thalassemia types:

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

Beta-Thalassemia smear

Beta-thalassemia differential diagnosis:

Treatment of thalassemia major:

1. These patients survive by the blood transfusion. It is tried to maintain the 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 RBCs survival and fewer reactions.
   3. 500 mL of blood contains 250mg of iron.
2. Regularly give the folic acid 5 mg/day.
3. There is a complication of the iron overload, which needs chelating therapy to control the 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 the blood.
   3. Give subcutaneously 40 mg/kg over 8 to 12 hours, 5 to 7 days weekly.
   4. This should be started in infants after the 10- to 15 units of the blood transfusion.
4. Excess iron causes skin pigmentation and damages the heart.
   1. Assessment of the iron status, advises:
   2. Serum ferritin.
   3. Serum iron.
   4. % saturation of transferrin.
   5. Serum non-transferrin bound iron.
   6. Bone marrow biopsy for reticuloendothelial stores by Perl’s stain.
   7. Liver biopsy for parenchymal and reticuloendothelial stores.
   8. Assessment of the tissue damage  caused by the iron overload:
      1. For heart damage by iron advice:
         1. X-ray chest.
         2. ECG, 24 hours monitoring.
         3. Echocardiography.
         4. Radionuclide scan to check left ventricular ejection.
      2. For liver damage by the iron advice:
         1. LFT.
         2. Liver biopsy.
         3. CT scan or MRI.
      3. For endocrine glands 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.
   9. Vitamin C 200 mg/day. This will help in the excretion of iron produced by deferoxamine.
   10. Immunization against the Hepatitis B virus.
   11. Allogenic bone marrow transplantation will give a permanent cure.
5. Infections are quite common in these patients and need treatment by antibiotics.