Identification of β-globin haplotypes linked to sickle hemoglobin (Hb S) alleles in Mazandaran province, Iran.

Carrier frequency of the βS allele has been reported to be 0.19% in Mazandaran province, northern Iran. Haplotype analysis of the βS allele helps trace the origin of its encoded hemoglobin (Hb) variant, Hb S, in a region. The aim of this study was to investigate the haplotypes associated with βS alleles in Mazandaran province. Capillary electrophoresis was carried out to detect individuals suspected to have a βS allele(s). DNA analysis (PCR-RFLP) was used for final confirmation. To identify 5' to 3' β-globin gene cluster haplotypes associated with βS alleles, family linkage analysis was applied. Six polymorphic sites (HincII 5' to ε, XmnI 5' to Gγ, HindIII in Gγ, HindIII in Aγ, HincII 3' to ψβ and AvaII in β) were investigated using the PCR-RFLP method. Five different haplotypes were linked to βS alleles, while βA alleles were associated with nine haplotypes. Among the βS alleles, 53.9% were associated with the Benin (----++) haplotype, and the Arab-Indian (+++-++) haplotype had the second-highest frequency (23%). Unlike southern provinces, where the Arab-Indian haplotype is prominent, the Benin haplotype is the most frequent haplotype in northern Iran, and this may represent a founder effect. Since the Benin haplotype does not carry the XmnI polymorphism 5' to the Gγ gene, which is responsible for high expression of Hb F, a severe form of sickle cell disease can be anticipated in patients that are homozygous for the βS allele in the northern region.