What are the major sickle genotypes?

Updated: May 12, 2021
  • Author: Joseph E Maakaron, MD; Chief Editor: Emmanuel C Besa, MD  more...
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Answer

SCD denotes all genotypes containing at least one sickle gene, in which HbS makes up at least half the hemoglobin present. Major sickle genotypes described so far include the following:

  • HbSS disease or sickle cell anemia (the most common form) - Homozygote for the S globin with usually a severe or moderately severe phenotype and with the shortest survival

  • HbS/b-0 thalassemia - Double heterozygote for HbS and b-0 thalassemia; clinically indistinguishable from sickle cell anemia (SCA)

  • HbS/b+ thalassemia - Mild-to-moderate severity with variability in different ethnicities

  • HbSC disease - Double heterozygote for HbS and HbC characterized by moderate clinical severity

  • HbS/hereditary persistence of fetal Hb (S/HPHP) - Very mild or asymptomatic phenotype

  • HbS/HbE syndrome - Very rare with a phenotype usually similar to HbS/b+ thalassemia

  • Rare combinations of HbS with other abnormal hemoglobins such as HbD Los Angeles, G-Philadelphia, HbO Arab, and others


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