Alpha thal defective or absent alpha chain synthesis; 4 genes on chromosome 16

  1. normal all 4 genes present
  2. normal variant or silent carrier 3/4 genes (can have mild microcytosis or normal)
  3. trait 2/4 genes (characterized by mild microcytic anemia & mild increase in RBC); Bart hb (gammax4) detectable within 1st months of life, then fades
  4. Hgb H dz 1/4 genes (characterized by lots of beta4 Hgb molecules = HbH), mod-severe microcytic anemia, splenomegaly, hyperbili, high retic); has some Hb Bart (more than 2 del dz)
  5. hydrops fetalis (Barts) 0/4 genes; 80-90% Hb Bart, embryonic Hb acts as O2 carrier, severe anemia, CHF, edema; usually stillborn

Beta thal variable levels of beta chain synthesis; 2 genes on chromosome 11

Hemoglobin E: beta-chain variant (alpha2 / beta2, 26Glu->Lys); prevalent in populations from Southeast Asia, particularly Thailand and Cambodia

  1. trait no anemia, but microcytic
  2. homozygous mild anemia, microcytic, no organomegaly
  3. E-beta-thalassemia similar to beta-thalassemia major; characterized by severe anemia, organomegaly from extramedullary hematopoiesis, and hemolysis; requires RBC transfusion


back to Anemia, General Approach

from CHLA board review 2005