PrP polymorphisms associated with natural scrapie discovered by denaturing gradient gel electrophoresis.
DNA samples from 153 sheep, including 29 natural scrapie cases, were screened for the prion protein (PrP) coding sequence using the PCR and denaturing gradient gel electrophoresis. Four predicted amino acid substitutions were found in the centre of the PrP coding region: 112 methionine→threonine, 136 alanine→valine, 154 arginine→histidine and 171 glutamine→arginine. These substitutions appeared mutually exclusive, defining 5 coding alleles. The mutant DNAs were sequenced. The 136 valine allele, substituting a highly conserved alanine residue in a homozygous or heterozygous state, was highly significantly related to susceptibility to natural scrapie. This relationship indicates that the 136 valine allele may modulate development of the disease, implying a pivotal role for PrP molecules in natural scrapie, as has been observed for experimental scrapie and human prion diseases.