Chronic wasting disease associated with prion protein gene (PRNP) variation in Norwegian wild reindeer (Rangifer tarandus)

Abstract

The emergence of CWD in Europe in 2016 and the first natural infection in wild reindeer warranted disease management. This led to the testing of 2424 hunted or culled reindeer during 2016-2018, from the infected subpopulation in the Nordfjella mountain range in Southern Norway. To identify any association between PRNP variation and CWD susceptibility, we characterized the open reading frame of the PRNP gene in 19 CWD positive reindeer and in 101 age category- and sex-matched CWD negative controls. Seven variant positions were identified: 6 single nucleotide variants (SNVs) and a 24 base pair (bp) deletion located between nucleotide position 238 and 272, encoding four instead of five octapeptide repeats. With a single exception, all variant positions but one were predicted to be non-synonymous. The synonymous SNV and the deletion are novel in reindeer. Various combinations of the non-synonymous variant positions resulted in the identification of five PRNP alleles (A-E) that structured into 14 genotypes. We identified an increased CWD risk in reindeer carrying two copies of the most common allele, A, coding for serine in position 225 (Ser225) and in those carrying allele A together with the 24 bp deletion.

Keywords: CWD; alleles; deer; disease management; disease susceptibility; gene frequency; genotype; prions; reindeer; risk.

Figure 1.

Localization of Nordfjella zones 1, 2 and other wild reindeer management areas in Southern Norway. All cases were detected in zone 1 and sampled in 2016–2018.

Figure 2.

Western blot analysis of PrP^C transiently expressed in human neuroblastoma SH-SY5Y cells. Samples were untreated (-) or deglycosylated by PNGase-F treated (+) SH-SY5Y cells, untransfected (SH-SY) and transfected clones with ovine PRNP (ovPrP), reindeer PRNP with 24 bp deletion (rePrP^del) and wild type reindeer PRNP (rePrP^wt). Deglycosylated bands from rePrP^del and rePrP^wt differ with 1 kDa as expected. The membrane was probed with anti-PrP mab P4.

Figure 3.

Comparison of PRNP genotype frequencies in cases (n = 19) and controls (n = 101). The relative frequencies between cases and controls were statistically different (P < 0.05, Fisher’s exact test). The plot background in white indicates genotypes found in both groups, and in grey, genotypes only found in controls. The B/B genotype was the most frequent genotype exclusive to controls and selected as the baseline for Firth logistic regression with CWD as an outcome and PRNP genotype as a predictor.

Figure 4.

Comparison of PRNP alleles’ relative frequency by CWD status in wild reindeer from Nordfjella zone 1, Norway. The relative allele frequencies between CWD cases (n= 19) and controls (n = 101) were statistically different (P < 0.05, Fisher’s exact test). The plot background in white frames genotypes found in cases and controls and in grey, genotypes only found in controls.