alpha thalassemia

Introduction

alpha-Globin gene synthesis is under control of 2 pairs of genes (total of 4). Four* alpha-thalassemias are:

Classification

• alpha-thalassemia-2 trait (alpha-thalassemia silent carrier)
  • deletion of a single alpha globin gene (there are 4 alpha globin genes. 2 on each chromosome)
  • an asymptomatic carrier state
• alpha-thalassemia-1 results from deletion or malfunction of 2 alpha globin genes.
  • anemia is mild, microcytic & hypochromic
  • cis form
    • deletion or malfunction of 2 genes on same chromosome
    • found in Asian & Mediterranean populations
    • hydrops fetalis found in these populations
  • trans form
    • affected genes on different chromosomes
    • found in African American populations
    • hydrops fetalis unlikely
• deletion or malfunction of 3 alpha globin genes
  • hemoglobin H disease (beta-globin tetramers)
  • moderately severe hemolytic anemia
  • chronic transfusions usually not required
• all 4 loci deleted or non-functional
  • hemoglobin Bart's (gamma-globin tetramers)
  • hydrops fetalis

* - alpha/ alpha alpha (i.e. 3 of 4 functional alpha globin genes is referred to as silent thalassemia

Epidemiology

• occur mostly in Mediterranean & Southeast Asian populations

Pathology

• imbalance in globin-chain production in adult hemoglobin A
• alpha chain production can range from none to very nearly normal levels

Laboratory

• complete blood count
  • microcytic anemia
  • RDW is normal (high in iron deficiency)
• peripheral smear
  • microcytosis, hypochromia, target cells
• hemoglobin electrophoresis: normal
  • hemoglobin A2 band is not increased (unlike beta-thalassemia)
  • there is no substitute for hemoglobin alpha chain
• globin chain synthetic ratios
• alpha thalassemia genotyping
  • HBA1 gene mutation
  • HBA2 gene mutation
  • HBA2 gene deletion

Management

• alpha-thalassemia trait (alpha-thalassemia minor) requires no treatment

More general terms

• thalassemia

More specific terms

• alpha thalassemia silent carrier
• alpha thalassemia-0 (homozygous alpha thalassemia)
• alpha thalassemia-1 (alpha-thalassemia trait, cis form)
• alpha thalassemia-2 (alpha-thalassemia trait, trans form)
• hemoglobin H disease

Additional terms

• alpha thalassemia genotyping
• alpha-globin gene
• alpha-thalassemia myelodysplasia syndrome
• X-linked alpha-thalassemia/mental retardation syndrome (ATR-X syndrome)

Patient information

alpha thalassemia patient information