Combined and differential effects of alpha‐thalassemia and HbF‐quantitative trait loci in Senegalese hydroxyurea‐free children with sickle cell anemia

Background Our objective was to investigate the combined and differential effects of alpha‐thalassemia –3.7 kb deletion and HbF‐promoting quantitative trait loci (HbF‐QTL) in Senegalese hydroxyurea (HU)‐free children and young adults with sickle cell anemia (SCA). Procedure Steady‐state biological parameters and vaso‐occlusive crises (VOC) requiring emergency admission were recorded over a 2‐year period in 301 children with SCA. The age of the first hospitalized VOC was also recorded. These data were correlated with the alpha‐globin and HbF‐QTL genotypes. For the latter, three different genetic loci were studied (XmnI, rs7482144; BCL11A, rs1427407; and the HBS1L‐MYB region, rs28384513) and a composite score was calculated, ranging from zero (none of these three polymorphisms) to six (all three polymorphisms at the homozygous state). Results : A positive clinical impact of the HbF‐QTL score on VOC rate, HbF, leucocytes, and C‐reactive protein levels was observed only for patients without alpha‐thalassemia deletion. Conversely, combination of homozygous –3.7 kb deletion with three to six HbF‐QTL was associated with a higher VOC rate. The age of the first hospitalized VOC was delayed for patients with one or two alpha‐thalassemia deletions and at least two HbF‐QTL. Conclusion Alpha‐thalassemia –3.7 kb deletion and HbF‐QTL are modulating factors of SCA clinical severity that interact with each other. They should be studied and interpreted together and not separately, at least in HU‐free children.