Abstract
Previous work has suggested that the βc mutation arose on a relatively rare βA chromosome with a unique haplotype, and these data have been used to postulate a single origin of the βc allele. Most characteristic of this haplotype has been the absence of a Hpa I recognition site 3′ to the β-globin gene. We studied 40 patients with Hb SC, 11 with Hb AC, and one with Hb CC. Complete haplotyping was possible on 44 βc alleles and βc haplotyping was possible on an additional four βc alleles. Our results support the predominence of a unique βc haplotype which is characterized by the absence of the Hpa I site. However, one patient who was homozygous for Hb C had one βc allele with an atypical haplotype which contained the Hpa I site. It is unclear at this time whether or not this represents a second origin of the βc mutation.