What is the pathophysiology of hemoglobinopathy retinopathy?

Updated: Sep 03, 2019
  • Author: Brian A Phillpotts, MD; Chief Editor: Hampton Roy, Sr, MD  more...
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Answer

Hemoglobin molecules are found exclusively in erythrocytes, where their main function is to transport oxygen to tissues. Hb A, the major hemoglobin in adults, is composed of 4 polypeptide chains, 2 alpha chains and 2 beta chains (alpha2 beta2) held by noncovalent bonds. The heme and the globin molecules together form hemoglobin, which can bind up to 4 oxygen molecules. The genes coding for alpha and beta globin chains are located on chromosome 16 and chromosome 11, respectively.

The widely accepted pathogenesis for sickle cell retinopathy is vasoocclusion that leads to retinal hypoxia, ischemia, infarction, neovascularization, and fibrovascularization. In sickle cell anemia, the amino acid substitution valine for glutamate occurs on the beta chain at the sixth position. This substitution, combined with conditions that may promote sickling (ie, acidosis, hypoxia), triggers the deoxygenated Hb S to polymerize, making the erythrocyte rigid. This rigidity is partially responsible for the vasoocclusion.

Vasoocclusion also is in part due to the interaction between sickled cells and the vascular endothelium. The adherence of sickled cells to the endothelium triggers an inflammatory process with the release of inflammatory agents. The activated endothelia are procoagulant, thereby inducing further adherence of sickled cells to the endothelium. The activated endothelium and rigid sickled cells bind to von Willebrand factor and thrombospondin, which is secreted by activated platelets. The result of this cascade is vascular stasis, hemolysis, and vasoocclusion of the capillary beds.


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