Structural Defects

Structural defects

95% of structural variants are caused by single amino acid replacement .This amino acid replacement or substitution changes the quality or characrtistics of haemoglobin. For example HbS, C, E, D, G, O all contain substitution of a different amino acid into the normal amino acid sequence of beta globin chain.

Sickle cell disease

Hemoglobin S

HbS substitution of Glutamic Acid at position 6 of the beta globin gene leading to the production of a defective form of hemoglobin S. HbS has a tendency to polymerize and deform the red blood cells into characteristic sickle cell.

Prevalence: Effects million throughout the world. Common in sub-Saharan Africa, Cuba, South America, Central America, Saudi Arabia, India, Mediterranean.

  • Homozygous sickle cell: HbSS
  • Heterozygous sickle cell: HbSA
  • Compound Heterozygous: HbSE, HbSE, HbD Punjab, HbS O Arab, HbS/HPFH, HbS/Beta Thal, HbS/alpha Thal.

Sickle Cell Disease Haplotypes

  • Senegal
  • Benin
  • Bantu
  • Asian

Pathophysiology

Deoxygenation of HbS leads to the conformational changes triggers the formation of large polymers that distorts red blood cells into a sickle shape and decreases the elasticity.

  • complex chronic inflammatory condition.
  • State of chronic activation of coagulation system.
  • Red cell membrane abnormalities.
  • Nitric oxide depletion
  • Increase whole blood viscosity

Clinical Manifestations Sickle Cell Disease

  • Anemia
  • Crisis
  • complications

Acute complications

  • Aplastic crisis
  • Acute chest syndrome
  • Acute splenic sequestration
  • Acute painful crisis
  • Priapism
  • Stroke
  • Recurrent Vasoclusive crisis
  • Papillary necrosis
  • Sepsis

Chronic complications

  • Anemia
  • Jaundice
  • Splenomegaly
  • Cardiomegaly
  • Cholithisais
  • Delayed growth
  • Pulmonary hypertension
  • Leg ulcers
  • Retinopathy
  • Avascular necrosis
  • Transfusion Hemosiderosis

Sickle Cell Disease Types of Crisies

  • Hemolytic crisis
  • Aplastic crisis
  • Sequestration crisis
  • Vasoclusive crises

Sickle Cell Disease Diagnostic Tools & Treatment

Diagnostic Tools

  • Peripheral blood finding.
  • Sickling test
  • Haemoglobin electrophoresis.
  • ESR .
  • Unconjugated bilirubin.
  • LDH & haptoglobin.
  • Newly born screening.
  • Prenatal diagnosis.

Sickle Cell Disease Treatment

  • Daily preventive measures.
  • Routine health care .
  • Infections.
  • Transfusion therapy.
  • Pain management.
  • New therapeutic modalities.
  • Hydroxyurea
  • Bone marrow transplantation.
  • Psychosocial issues.
  • Gene therapy.
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