Alpha thalassemia

• Will be expressed in feti, as  chains are needed for HbF

• In the newborn, the unpaired  globulin chains form tetramers called Hb Bart's; in the adult, the excess  globin chains form tetramers called HbH

• There are 2 pairs of  chain genes (i.e., 4 genes) on chromosome 16; the severity of the disease depends on how many genes are affected

  • Most common thing that goes wrong is a deletion; each gene contributes about 25% of the  chains, and each can be deleted independently

  • A silent carrier state results from deletion of one gene

  •  thalassemia trait comes from deletion of 2 genes

    • These patients may be slightly anemic, RBC microcytotic, but will have a normal electrophoresis, since all Hb types are equally affected

    • The genes can be form the same chromosome (Asian type) or can be one from each of the chromosomes (African type); those with the Asian type are at an increased risk of producing messed up kids

  • HbH disease

    • Deletion of 3 genes

    • Most common in Asian populations

    • Moderate in severity, it may be confirmed by showing HbH on electrophoresis or by staining of RBC inclusions by brilliant cresyl blue

  • Hydrops fetalis

    • All 4 genes gone

    • Without  chains, HbF cannot be formed; the free  chains form Hb Bart’s, which has a very high affinity for O₂, not allowing it to be delivered to the fetus

    • Results in intrauterine death

Category: Medical Subject Notes , Pathology Notes