Characterization of PRNP and SPRN coding regions from atypical scrapie cases diagnosed in Poland

PrP gene polymorphism and its influence on some productive traits of sheepbreeds reared in Bulgaria

The rapiddissemination of scrapie over the past few decades led to development of aspecific eradication programme, based on the polymorphisms within the prionprotein gene (PRNP). Current approach encourages the selection ofanimals carrying the resistant ARR/ARR genotype, while other genotypes areconsidered less preferable. Although the strategy seems to be working quitewell, farmers are concerned whether this will affect sheep productivity andsubsequently decrease net profits. The current study was aimed to elucidatethe linkage between the PrP gene polymorphism (based on codons 136,154 and 171) and some productive traits (live weight, reproduction, milk andfleece yield) of three sheep breeds reared in Bulgaria – Assaf, NortheastBulgarian Merino and Blackhead Pleven. The total number of detectedgenotypes was six – ARR/ARR, ARR/ARQ, ARR/ARH, ARQ/ARQ, AHQ/ARQ and ARR/VRQ,with different prevalence within each breed. The observed lack ofsignificant differences in the studied performance traits between the PRNP genotypes suggests that PRNP polymorphisms did not influencethe sheep productive performance. Therefore, selection of animals on theresistant genotype (ARR/ARR) would not worsen their productivity. Theobtained results should help the better understanding of scrapie selectionand the positive effect that it would have to both health care and industry.

Classic and atypical scrapie - a genetic perspective

Scrapie was the first prion disease to be recognised and the study of this disease in sheep and goats has provided a wealth of information not only for scrapie but also for the other prion diseases. All prion diseases are under strong genetic control of the prion gene PRNP, independent of whether they are typical or atypical scrapie and which of the different prion strains is causing infection. Decades of studies using experimental disease challenges and field surveys have established disease association models, in which species-specific amino acid variations in the prion or PrP protein, encoded by the PRNP gene, can predict disease susceptibility or resistance. PRNP genetics represents an important and successful basis for implementing scrapie eradication strategies in sheep and goats. In general terms these studies have revealed that there appear to be many more amino acid changes in PrP leading to increased resistance than to higher susceptibility. Most changes are in the globular part of PrP protein and three regions appear to have major influence. This knowledge can be transferred into prion diseases of other species to facilitate genetic control strategies. However, an obstacle remains with the lack of fully understanding the underlying molecular mechanism, impeding our ability to deal with the difference in the genetic control between typical and atypical forms of scrapie or to predict association in newly infected species. This chapter will discuss the advances in both typical and atypical scrapie from a genetic perspective.

Genotyping and surveillance for scrapie in Finnish sheep

Background

The progression of scrapie is known to be influenced by the amino acid polymorphisms of the host prion protein (PrP) gene. There is no breeding programme for TSE resistance in sheep in Finland, but a scrapie control programme has been in place since 1995.

In this study we have analysed PrP genotypes of total of 928 purebred and crossbred sheep together with the data of scrapie survey carried out in Finland during 2002–2008 in order to gain knowledge of the genotype distribution and scrapie prevalence in Finnish sheep.

Results

The ARQ/ARQ genotype was the most common genotype in all breeds studied. ARR allele frequency was less than 12% in purebred Finnish sheep and in most genotypes heterozygous for ARR, the second allele was ARQ. The VRQ allele was not detected in the Grey race sheep of Kainuu or in the Aland sheep, and it was present in less than 6% of the Finnish Landrace sheep. Leucine was the most prominent amino acid found in codon 141. In addition, one novel prion dimorphisms of Q220L was detected. During the scrapie survey of over 15 000 sheep in 2002–2008, no classical scrapie cases and only five atypical scrapie cases were detected.

Conclusions

The results indicate that the Finnish sheep populations have genetically little resistance to classical scrapie, but no classical scrapie was detected during an extensive survey in 2002–2008. However, five atypical scrapie cases emerged; thus, the disease is present in the Finnish sheep population at a low level.