DNA polymorphisms in the controlling region of the human haptoglobin genes: a molecular explanation for the haptoglobin 2-1 modified phenotype.
A haptoglobin 2-1 modified (Hp2-1mod) phenotype results when the amount of Hp2 polypeptide synthesized in Hp2/Hp1 heterozygotes is less than that of Hp1 polypeptide. Cloned Hp2 DNA from an individual with the Hp2-1mod phenotype is here shown to have a C in place of the normal A at nucleotide position -61 in one of the interleukin-6 (IL-6) responsive elements of the haptoglobin promoter region. Direct sequencing of the haptoglobin promoter region, amplified by PCR, from DNA from unrelated American blacks showed a C at -61 in all of 10 individuals with the Hp2-1mod phenotype, in two of four with a "possible Hp2-1mod" phenotype, but in none of 15 with the Hp2-1 phenotype. Thus the -61C mutation in the Hp2-61C allele is strongly associated with the Hp2-1mod phenotype. Sequencing results also show that there are three other promoter sequences in the population studied; each can be associated with either Hp2 or Hp1. The variability seen in the Hp2-1mod phenotype, a variability which ranges from close to Hp2-1 to close to Hp1-1, can be explained, in part, by the existence of several Hp2 alleles differing in their promoters--and possibly, in part, by differences in the promoters of the accompanying Hp1 allele. A further part of the variability may be the consequence of differences in the way that the Hp2-61C and the Hp2 alleles respond to the IL-6-dependent factor during an acute-phase response.
Maeda
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Department of Pathology and Genetics Curriculum, University of North Carolina, Chapel Hill 27599-7525.
D001483:Base Sequence; D004247:DNA / Q000235:genetics*; D005838:Genotype; D006242:Haptoglobins / Q000737:chemistry / Q000235:genetics*; D006579:Heterozygote; D006801:Humans; D008969:Molecular Sequence Data; D010641:Phenotype; D011110:Polymorphism, Genetic / Q000235:genetics*; D011401:Promoter Regions, Genetic / Q000235:genetics*
D006242:Haptoglobins; D004247:DNA