Haplotypes in SS patients from Nigeria; characterization of one atypical β^S haplotype no. 19 (Benin) associated with elevated HB F and high^Gγ levels

We have determined the haplotypes of 669 βS and 109 βA chromosomes from numerous members of 297 Nigerian families of various ethnic backgrounds. Among the βS chromosomes, haplotype 19 was detected in 93.2%, haplotype 17 in 3.4%, and haplotype 20 in 0.1%, while 2.4% represented atypical haplotypes. As many as 60.6% of the βA chromosomes exhibited haplotype 19 mutations, 8.2% had haplotype 3, and 1.8% had haplotype 20. Two siblings with elevated Hb F andGγ levels were heterozygous for a βS chromosome with haplotype 19 and a second chromosome with a hybrid haplotype (termed 19B). In this hybrid chromosome, haplotype 3-like locus control region (LCR) [hypersensitive site-2 (HS-2)] sequences are in juxtaposition to those of the 5′ flanking region of theGγ promoter of a βS chromosome with haplotype 19. The presence of this hybrid chromosome is associated with highGγ values in individuals with both sickle cell anemia (SS) and sickle cell trait (AS); it closely resembles another hybrid βS chromosome, termed 19 A, observed in a previously reported Turkish SS patient who was homozygous for this chromosome and had high Hb F and highGγ values. In both instances, it is hypothesized that the haplotype 3-like sequences of the LCR HS-2 contain genetic determinants that can combine with factors produced during hematopoietic stress, resulting in increased γ-globin gene expression. © 1992 Springer-Verlag.