Allele frequency of Hemoglobin S among patients with uncomplicated Plasmodium falciparum malaria in N'Djamena, Chad

Protection against malaria induced by the sickle cell trait has been a major example of genetic selection for over half a century. It has been demonstrated that human populations in Africa have acquired a high frequency of haemoglobin S (HbS) allele because the heterozygous genotype (sickle cell trait) provides protection against the severe symptoms of Plasmodium falciparum infection leading to lower parasite numbers and increased clearance of infected cells by the body. However, there is scarcity of data from Chad. This study was conducted to determine the HbS allele frequency, and also to assess the possible protection, in subjects with uncomplicated malaria from N’Djamena, Chad. Dry blood spot samples were collected from patients with uncomplicated Plasmodium falciparum malaria, whose infection was identified by microscopy. To assess HbS allele frequency, human DNA was analyzed by PCR-RFLP. We collected samples from 320 (2/3 females) uncomplicated falciparum malaria cases, among which the allele frequency of the HbS variant allele was 6.72%. Not significant association with the parasite density was found among the different HbS genotypes. This result confirms a non-negligible frequency of the HbS allele in the study population, providing for the first time data from Chad. The present report provides some information on the sickle prevalence in the study population but can not be interpreted as being representative of the wider population, since the subjects were recruited in a malaria survey.