The occurrence of α chain gene deletions and triplications among pediatric Hb S homozygotes

Abstract

Approximately 40% of more than 100 young Hb S homozygotes attending the Pediatric Clinic of the Comprehensive Sickle Cell Center of the Medical College of Georgia in Augusta have an associated α-thalassemia-2 (α-thal-2) heteroztgosity, i.e. the -α/-α; βs/βs condition, or homozygosity, i.e. the -α/-α; βs/βs condition. These conditions are documented by pulse incubations of peripheral blood reticulocytes and by gene mapping using recombinant DNA probes. All α-thal-2 deletions are associated with a 16 Kb Bgl II α chain DNA fragment which arises from a deletion of the 3' end of the α2 gene, the 5' end of the α1 gene and includes the intergenic DNA. Fusion of the residual 3' and 5' ends of the α2 and α1 genes results in a single active a chain gene, i.e. the -3.7 Kb or Rightward type of deletion. Its 3' sequences belong to the α1 gene. The homozygosity for the condition and Hb S is characterized by higher Hb levels without an accompanying increase of Hb F percentages; a distinct microcytosis and hypochromia; splenomegaly and decreased α/non-α values.