Prion protein polymorphisms in white-tailed deer influence susceptibility to chronic wasting disease

The primary sequence of the prion protein affects susceptibility to transmissible spongiform encephalopathies, or prion diseases, in mice, sheep and humans. The Prnp gene sequence of free-ranging, Wisconsin white-tailed deer was determined and the Prnp genotypes of chronic wasting disease (CWD)-positive and CWD-negative deer were compared. Six amino acid changes were identified, two of which were located in pseudogenes. Two alleles, a Q -> K polymorphism at codon 226 and a single octapepticle repeat insertion into the pseudogene, have not been reported previously. The predominant alleles - wild-type (Q95, G96 and Q226) and a G96S polymorphism - comprised almost 98% of the Prnp alleles in the Wisconsin white-tailed deer population. Comparison of the allelic frequencies in the CWD-positive and CWD-negative deer suggested that G96S and a Q95H polymorphism were linked to a reduced susceptibility to CWD. The G96S allele did not, however, provide complete resistance, as a CWD-positive G96S/G96S deer was identified. The G96S allele was also linked to slower progression of the disease in CWD-positive deer based on the deposition of Prp(CWD) in the obex region of the medulla oblongata. Although the reduced susceptibility of deer with at least one copy of the Q95H or G96S allele is insufficient to serve as a genetic barrier, the presence of these alleles may modulate the impact of CWD on white-tailed deer populations.