α- Thalassemia

• α- thalassemia is maily caused due to deletion of one or more α- genes located on short arm chromosome 16.
• It may depress the production of haemoglobin that contains α- chain i.e. HbA, HbA₂, HbF.
• These are due to inherited defects that reduce α- globin synthesis.

 Classification of α- thalassemias–

1. Four α- gene deletion- Hb Bart’s hydrops foetalis
2. Three α- gene deletion- HbH disease
3. Two α- gene deletion- α- thalassemia trait
4. One α- gene deletion- α- thalassemia trait (carrier) 

1. Hb Bart’s hydrops foetalis-

• Deletion of all four α- chain genes.
• It causes most severe form of α- thalassemia.
• Hb Bart’s is a gamma globin chain tetramer.

Clinical features-

• Severe tissue hypoxia
• Infant dies shortly after birth
• Rh haemolytic disease

Lab findings-

• Severe  anemia
• Blood film shows– anisopoikilocytosis, hypochromia, microcytosis, polychromasia, basophilic stippling, target cells.
• Reticulocyte count is high
• Serum bilirubin level high

2. HbH disease-

• Deletion of three α- globin genes forms HbH.
• HbH is precipitated as Heinz bodies within affected red cells.
• Hb constant spring is an elevated α- chain variant of HbH disease.

Clinical features-

• Haemolytic anemia
• Splenomegaly
• Cholelithiasis

Lab findings-

• Moderate anemia
• Blood films- microcytosis, hypochromia, basophilic stippling, target cells.
• HbH inclusions as Heinz bodies with brilliant cresyl blue stain.

3. α- thalassemia trait-

• Two α- globin genes are deleted.

Clinical features-

• Refactory microcytic hypochromic anemia

Lab diagnosis-

• Haemoglobin mildly reduced.
• Blood films shows microcytic, hypochromic red cell morphology.
• MCV, MCH, MCHC reduced.

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