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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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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