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Genetic Mutations

SCD results from several genetic mutations that affect the human b-globin gene. The characteristic defect is a single point mutation, an AŽT base transversion (GAG/GAAŽ GTG/GTA) in the 6th codon of the b-globin gene. This SCD mutation is termed bS, and results in a single amino acid substitution, b6 GluŽVal. The mutant Hb protein (gene product) is referred to as Hb S[17]. The sickle mutation can occur in the homozygous state, which is classically termed sickle cell anemia or Hb SS (bS/bS)[17]. In addition, SCD can occur in (compound) heterozygous states wherein the bS mutation is present concurrently with other b-globin gene mutations (e.g., bS/bC, bS/bthal, bS/bO-Arab, bS/bD-Punjab,  bS-Antilles)[17-21]. Important pro-sickling mutations include the bAntilles (b23 ValŽIle) and bD-Punjab (b121 GluŽGln) mutations.