High level of heterozygous haplotype of hemoglobin in Abidjan population with mild malaria

Sickle cell disease (SCD) is a hemoglobin disorders that concern 300,000 newborns each year around the world. There are hemoglobin haplotypes that affect SCD clinic expression. Our goal was to identify the hemoglobin’s haplotypes among individuals with mild malaria independently of SCD status in Côte d’Ivoire. To determine these haplotypes, specific restriction enzyme (RE) is used after PCR amplification with each primer. According to the digestion of PCR product by RE, five hemoglobin’s haplotypes are found in the world. In Côte d’Ivoire, no study has yet deeply described the distribution of haplotypes. Four different “classical” haplotypes of hemoglobin were detected: Benin (56.5%), Bantou (28.5%), Senegal (4%), Cameroun (1%); and 10% of atypical profiles. Heterozygous haplotype (69%) were more frequent than homozygous haplotype (31%). In this preliminary study, we note a high prevalence of atypical and heterozygous haplotype. Benin haplotype that is associated with severity of SCD was most predominant in our studied population.


Background
Sickle cell disease (SCD) is a hemoglobin disorders that concerns 300,000 newborns each year around the world [1]. Sub-Saharan's countries harbored the highest prevalence with S hemoglobin in Central Africa and C in Sahelian areas [2][3][4]. There are hemoglobin haplotypes that affect SCD clinic expression. These haplotypes have different origins [5,6] and some studies indicated the relation between SCD clinics manifestations and hemoglobin haplotypes. In fact, the presence of some haplotypes reduce the SCD symptoms; and other haplotypes amplify the clinics manifestations [7][8][9][10][11][12][13][14]. To determine these haplotypes, specific restriction enzymes (RE) are used after PCR amplification. Relative to the digestion of PCR product by RE; there are five hemoglobin's haplotypes around the world: Bantou (CAR), Arabic, Senegal, Cameroun and Benin [15,16]. In Côte d'Ivoire, no study has yet deeply described the distribution SCD haplotypes. Here we conducted a retrospective preliminary study in Côte d'Ivoire to identify the hemoglobin's haplotypes among individuals with mild malaria independently to SCD status.

Sample collections
Abidjan is the economic capital of Côte d'Ivoire with five million inhabitants from a large number of Open Access *Correspondence: rjambou@pasteur.fr 3 Global Health Department, Institut Pasteur, 25 rue Dr Roux, 75015 Paris, France Full list of author information is available at the end of the article neighboring countries. Participants were recruited from CSUCOM Anonkoua-Kouté (Abidjan, Abobo) in 2013 and 2016 among patients attending the center with mild malaria (parasitemia more than 2000 parasites/µL blood).
The hemoglobin status of the patients was determined based on a standard acetate electrophoresis of hemoglobin using Sebia ® Hemoglobin electrophoresis, following the protocol of the manufacturer.For molecular typing, 50 µL of total blood was dried on 5 M Whatman ® paper and stored in zip locked bag contained silicate gel until use in 2020.

Haplotype molecular typing
The hemoglobin electrophoresis was performed following the manufacturer's recommendations with total blood. For molecular typing, DNA purification was performed on blood spots using the Qiagen ® Blood Minikit as recommended by the manufacturer. For amplification, different programs were used according to the couple of primers used. Nine pairs of primers have been used following Sutton and co [15] and Doupa and co [17] ( Table 1). After amplification, each type of PCR products was digested with a related restriction enzyme (RE). The haplotype profiles were identified according to Sutton and co [15] and Doupa and co [17]. (Table 2).

Demographic results
Of the total 100 patients included in the study, 55% were women. The average age of the patients recruited was 14.5 years.
All participants with AC or CC genotypes were from the Benin group (homozygote Benin/Benin or Benin/ Bantu) whereas AS was found in the Bantu group (Table 3). Atypic, Cameroun and Senegal haplotypes were observed only in normal hemoglobin group (Table 3).

Discussion
Several authors have highlighted the interest of studying hemoglobin haplotypes for individuals with hemoglobin disorders as a modulation of the clinical profile of the disease [7][8][9][10][11][12][13][14]. In Côte d'Ivoire, there is not available data on hemoglobin haplotypes. This study updates data on hemoglobin haplotypes in Côte d'Ivoire amongst individuals living in Abidjan and experimenting mild malaria. During this work, women represented the highest proportion of people attending dispensaries. This is frequently observed as men use to practice self-treatment so they rarely visit dispensaries. Our study indicated a prevalence of 13% of sickle cell trait (3% of SCD) in the population analyzed. Previous studies conducted by Tossea et al. [18] in the same area reported a similar prevalence. This concordance could be due to the design of the two (02) studies. Indeed, these studies were carried out in individuals with middle malaria in Abidjan.
The Benin haplotype was the most prevalent followed by the Bantu one, which can be attributable respectively to ethnic origin of the population in Abidjan, and the high level of migration from central Africa to Ivory Coast. Arab-Indian haplotype was not observed despite migration of populations across the Sahel (Peul and Toucouleur ethnics). A small prevalence of Senegal and Cameroon haplotypes was observed. These different prevalence are in accordance with the geographical distribution of the different populations [5,6].
Similar to the studies of several authors who reported 5-10% of atypical haplotypes [9,[19][20][21], we found 10% of atypical haplotypes in the population of Abidjan, mostly associated with the Benin haplotype. Due to the fact that the Benin haplotype is associated with a more severe form of expression of SCD and considering the high prevalence of atypical haplotypes, the relationship between these haplotypes and the clinical pattern of sickle cell disease should be investigate further. Overall a high proportion of heterozygous genotype (61%) was found in Abidjan. That differs from the studies conducted by Doupa et al. (32%) [17]. This difference could be due to their selection of patients harboring SCD and to the limitation of that study to only a single restriction site.
The emergence of these atypics haplotypes and the high proportion of heterozygous haplotypes could support a high level of mixed populations. Indeed, Abidjan is one of the major city in West Africa, with a cosmopolite population. In addition, the important mixing of populations would be a factor in the development of genetic phenomena such as chromosomal recombination's between haplotype.
Different atypical haplotypes observed show strong similarities with the Benin and Bantu haplotypes. Several others authors [19,22,23] obtained similar results relative to atypical haplotypes. The high proportion of atypical haplotype and its similarity with the Benin haplotype could be explained by selection pressure. Indeed, the association of the atypical haplotypes with the more severe Benin haplotype may lead to a more moderate expressive expression of sickle cell disease. More insight studies need to be conducted to explore such associations and their clinic expressions.

Conclusion
In this preliminary study, we note a high prevalence of atypical and heterozygous haplotype. Benin haplotype that is associated with severity of SCD was most predominant in our studied population. Further studies involving a large number of SCD participants could help to estimate an accurate prevalence of hemoglobin haplotypes in Côte d'Ivoire.
Author contributions TASK conducted the laboratory study and wrote the manuscript; AAG, AABA and BC participated in the collection of the blood sampling; AEG participated to the PCR design; AKA ADA realized the laboratory study; BSEG. and OAT participated to the study design and reviewed the manuscript; RJ supervised the study, obtained the ethic clearance and the founds, wrote the protocol and co-wrote the manuscript. All authors read and approved the final manuscript.

Funding
This study and Tosséa A. Stéphane Koui were supported by the Rotary International Foundation.