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Document Type

Article

Anticipated Volume

96

Anticipated Issue

2

Abstract

Sickle cell anemia (SCA) occurs in individuals who are homozygous for the sickle hemoglobin (HbS) allele. The haplotypes of the HbS alleles can be traditionally ascertained through the analysis of five to eight informative restriction fragment length polymorphisms (RFLPs) within the HBB gene cluster, defining the five major HbS haplotypes, commonly referred to as Bantu or Central African Republic (BAN/CAR), Benin (BEN), Cameroon (CAM), Senegal (SEN), and Arab-Indian (AI). In a recent study, it was suggested that four single-nucleotide polymorphisms (SNPs)—rs3834466, rs28440105, rs10128556, and rs968857—are sufficient to characterize most of the HbS haplotypes. In the present study, we investigated the HbS haplotypes in a population sample from São Tomé e Príncipe (Central Africa) by analyzing this set of four SNPs. Additionally, we included the HBG2 rs7482144 (-158C>T) SNP, which is commonly used in the classical HbS haplotype classification, to compare the HbS haplotypes derived from the two different plex systems. Blood samples of 50 heterozygous (HbAS), nine homozygous (HbSS) and three normal HbAA individuals were engaged in this study. Genotyping was performed by the polymerase chain reaction (PCR)-RFLP method. Haplotypes were derived using the Arlequin software. In the 4-plex system, seven different haplotypes were inferred among the 68 HbS chromosomes, corresponding to: CAR 36.8%, BEN 25.0%, CAM 13.2%, SEN 11.8%, and three different sets of unknown HbS haplotypes (11.4%). The further inclusion of rs7482144 (XmnI) led to the inference of a total of eight distinct HbS haplotypes as follows: CAR 36.8%, BEN 25.0%, CAM 13.2%, SEN 8.8%, and into four different clusters of unknown HbS haplotypes (16.2%). Using only the nine homozygous HbSS individuals, the same five different haplotypes were identified for both systems, with all common haplotypes occurring at equal frequencies: CAR 27.8%, BEN 38.9%, CAM 16.7%, and SEN 11.1%. One atypical haplotype was identified at a frequency of 5.6%. Our findings suggest that the 4-plex system may not be entirely accurate in identifying the SEN haplotype when considering heterozygous individuals for the HbS allele in the study population. Additionally, the haplotype background of HbS observed in the S. Tomean population provided further insights compared to previous reports.

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