In the January 2013 issue of this Journal, Joly and Colleagues have described an unusual case of sickle cell trait.1 The patient, originating from Ivory Coast, exhibits a low HbS level (12%) with no phenotypic manifestations. The mutation was found on a β-globin cluster haplotype of the Benin type. The Authors argued that the low percentage of HbS in circulating blood results from a somatic deletion of the HBB gene bearing the βS mutation. Surprisingly, the patient’s relatives (mother and son) display a higher, yet unusually low HbS level of approximately 34–35%.
A very similar case had been described some years ago when a Moroccan female exhibited a low HbS level of approximately 11%.2 The βS chromosome haplotype was also of the Benin type. Molecular analyses have demonstrated the occurrence of a point mutation at the promoter element CACCC (CACCC → CATCC) in cis of the sickle cell mutation.3 One would wonder whether the authors of the recent work on the Ivorian case have extended the sequencing analysis down to the promoter region of the βS-globin allele.
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