Allelic variants at codon 146 in the PRNP gene show significant differences in the risk for natural scrapie in Cypriot goats

Evaluation of the application of the Czech Republic to be recognised as having a negligible risk of classical scrapie

The Czech Republic submitted a request to the European Commission to be recognised as a Member State with negligible risk of classical scrapie. EFSA has been asked to assess if the Czech Republic in its application has demonstrated for a period of at least 7 years (2015-2021) and proposed for the future, that a sufficient number of ovine and caprine animals over 18 months of age, representative of slaughtered, culled or found dead on farm animals, have been and will continue to be tested annually to provide a 95% level of confidence of detecting classical scrapie if it is present in that population at a prevalence rate exceeding 0.1%. A risk-based approach using stochastic scenario-tree modelling accounting for surveillance stream and species was applied. There is still a lack of data on the actual performance of the approved tests under field conditions, especially in sheep. Therefore, alternative scenarios were explored extending the range from the sensitivity provided by the past European Union evaluations of diagnostic screening tests to a sensitivity of 50%, consistent with published data obtained under field conditions in infected goat populations. Using data provided by the Czech Republic for 2015-2022, the estimated parameters of the scenario-tree model, the range of values of diagnostic sensitivity and applying the criterion for the 95% confidence level, it is concluded that the Czech Republic has tested annually a sufficient number of small ruminants to meet the requirement, for all combinations of years and diagnostic sensitivity scenarios except for 60% diagnostic sensitivity in 2021 and 2022, and 50% in 2015, 2016 and 2018-2022. Based on the proposed number of samples to be tested in 2023 and future years, the Czech Republic would test a sufficient number of animals to meet the requirement for all combinations of diagnostic sensitivity, except for the 50% scenario.

Genetic Variation in the Prion Protein Gene (PRNP) of Two Tunisian Goat Populations

Simple Summary

Goat production is contributing to the economic and social development of rural areas in arid lands, within harsh conditions of Southern Tunisia. In this geographic zone, there are two caprine populations: the native goat population and the crossed goat population. Genotyping goats for the prion protein gene (PRNP) allows us to estimate their level of genetic susceptibility to scrapie disease. In the present work, the Sanger sequencing method of the entire PRNP coding sequence was used to determine the different PRNP genotypes and haplotypes in two populations (116 animals). This study represents the first investigation on goats’ PRNP genetic variability in Tunisia, and the results are useful in the design of national breeding programs.

Abstract

Scrapie is a fatal prion disease. It belongs to transmissible spongiform encephalopathies (TSEs), and occurs in sheep and goats. Similarly, to ovine species, the prion protein gene (PRNP) plays a major role in conferring resistance or susceptibility to TSE in goats. This study assesses the variability of PRNP in native and crossed-breed goat populations raised in the Southeast of Tunisia and provides information on the distribution of PRNP haplotypes and genotypes in these goat populations. A total of 116 unrelated goats including 82 native and 34 crossed-breed goats were screened for PRNP polymorphisms using Sanger sequencing. Sequence analysis revealed 10 non-synonymous polymorphisms (G37V, M137I, R139S, I142M, H143R, N146D, R154H, R211Q, Q222K, and S240P), giving rise to 12 haplotypes and 23 genotypes. Moreover, four silent mutations were detected at codons 30, 42, 138, and 179; the former was reported for the first time in goat (nucleotide 60 c→t). Interestingly, the PrP variants associated with resistance (D146 and K222) or with a prolonged incubation time of goat to scrapie (M142, R143, H154, Q211) were absent or detected with low frequencies except for H154 variant, which is present with high frequency (1%, 1%, 4%, 0%, 88%, and 6%, respectively, for native goats, and 0%, 1%, 0%, 1%, 78%, and 1%, respectively, for crossed goats). The analysis of PRNP polymorphisms of goats raised in other regions of the country will be useful in getting a global view of PRNP genetic variability and the feasibility of goat breeding programs in Tunisia.

Evaluation of proteinase K-resistant prion protein (PrPres) in Korean native black goats carrying a potential scrapie-susceptible haplotype of the prion protein gene (PRNP)

Prion disease is a fatal neurodegenerative disease with a broad host range in humans and animals. It is caused by proteinase K-resistant prion protein (PrPres). In previous studies, a heterogeneous infection in Cervidae and Caprinae was reported. Chronic wasting disease (CWD) has been frequently reported as the only prion disease in Korea that occurs in livestock. Thus, there is a possibility of transmission of CWD to Korean native black goats. However, PrPres has not been investigated thus far in Korean native black goats. We found strong linkage disequilibrium between c.126G>A and c.414T>C (r2 = 1) and between c.718C>T and c.126G>A (r2 = 0.638). In addition, the haplotype GTGTAAAC (representing codons 42, 102, 127, 138, 143, 146, 218 and 240) showed the highest frequency with 45.1%. Among 41 Korean native black goats, 20 animals (48.78%) were homozygous for the susceptible haplotypes (histidine at codon 143, asparagine at codon 146 and arginine at codon 154). Interestingly, we did not detect PrPres bands in any of the tested animals, including the 20 animals carrying potential scrapie susceptible haplotypes.

The Scrapie Prevalence in a Goat Herd Is Underestimated by Using a Rapid Diagnostic Test

Current European surveillance regulations for scrapie, a naturally occurring transmissible spongiform encephalopathy (TSE) or prion disease in sheep and goats, require testing of fallen stock or healthy slaughter animals, and outline measures in the case of confirmation of disease. An outbreak of classical scrapie in a herd with 2500 goats led to the culling of the whole herd, providing the opportunity to examine a subset of goats, take samples, and examine them for the presence of disease-associated prion protein (PrPSc) to provide further information on scrapie test sensitivity, pathology, and association with prion protein genotype. Goats were examined clinically prior to cull, and the brains examined post mortem by Bio-Rad ELISA, a rapid screening test used for active surveillance in sheep and goats, and two confirmatory tests, Western blot and immunohistochemistry. Furthermore, up to 10 lymphoid tissues were examined by immunohistochemistry. Of 151 goats examined, three (2.0%) tested positive for scrapie by ELISA on brain, confirmed by confirmatory tests, and a further five (3.3%) were negative by ELISA but positive by at least one of the confirmatory tests. Only two of these, both positive by ELISA, displayed evident signs of scrapie. In addition, 10 (6.6%) goats, which also included two clinical suspects, were negative on brain examination but had detectable PrPSc in lymphoid tissue. PrPSc was detected most frequently in the medial retropharyngeal lymph node (LN; 94.4% of all 18 cases) and palatine tonsil (88.9%). Abnormal behavior and circling or loss of balance when blindfolded were the best clinical discriminators for scrapie status. None of the goats that carried a single allele in the prion protein gene associated with increased resistance to scrapie (Q211, K222, S146) were scrapie-positive, and the percentage of goats with these alleles was greater than expected from previous surveys. Significantly more goats that were scrapie-positive were isoleucine homozygous at codon 142 (II142). The results indicate that the sensitivity of the applied screening test is poor in goats compared to the confirmatory tests as gold standard, particularly for asymptomatic animals. Sensitivity of surveillance could be improved by testing retropharyngeal LN or palatine tonsil in addition to brain.

Goats naturally devoid of PrPC are resistant to scrapie

Prion diseases are progressive and fatal, neurodegenerative disorders described in humans and animals. According to the "protein-only" hypothesis, the normal host-encoded prion protein (PrPC) is converted into a pathological and infectious form (PrPSc) in these diseases. Transgenic knockout models have shown that PrPC is a prerequisite for the development of prion disease. In Norwegian dairy goats, a mutation (Ter) in the prion protein gene (PRNP) effectively blocks PrPC synthesis. We inoculated 12 goats (4 PRNP+/+, 4 PRNP+/Ter, and 4 PRNPTer/Ter) intracerebrally with goat scrapie prions. The mean incubation time until clinical signs of prion disease was 601 days post-inoculation (dpi) in PRNP+/+ goats and 773 dpi in PRNP+/Ter goats. PrPSc and vacuolation were similarly distributed in the central nervous system (CNS) of both groups and observed in all brain regions and segments of the spinal cord. Generally, accumulation of PrPSc was limited in peripheral organs, but all PRNP+/+ goats and 1 of 4 PRNP+/Ter goats were positive in head lymph nodes. The four PRNPTer/Ter goats remained healthy, without clinical signs of prion disease, and were euthanized 1260 dpi. As expected, no accumulation of PrPSc was observed in the CNS or peripheral tissues of this group, as assessed by immunohistochemistry, enzyme immunoassay, and real-time quaking-induced conversion. Our study shows for the first time that animals devoid of PrPC due to a natural mutation do not propagate prions and are resistant to scrapie. Clinical onset of disease is delayed in heterozygous goats expressing about 50% of PrPC levels.

Transmissible spongiform encephalopathy in goats: is PrP rapid test sensitivity affected by genotype?

Transmissible spongiform encephalopathy (TSE) surveillance in goats relies on tests initially approved for cattle, subsequently assessed for sheep, and approval extrapolated for use in "small ruminants." The current EU-approved immunodetection tests employ antibodies against various epitopes of the prion protein PrPSc, which is encoded by the host PRNP gene. The caprine PRNP gene is polymorphic, mostly at codons different from the ovine PRNP. The EU goat population is much more heterogeneous than the sheep population, with more PRNP-related polymorphisms, and with marked breed-related differences. The ability of the current tests to detect disease-specific PrPSc generated against these different genetic backgrounds is currently assumed, rather than proven. We examined whether common polymorphisms within the goat PRNP gene might have any adverse effect on the relative performance of EU-approved rapid tests. The sample panel comprised goats from the UK, Cyprus, France, and Italy, with either experimental or naturally acquired scrapie at both the preclinical and/or unknown and clinical stages of disease. Test sensitivity was significantly lower and more variable when compared using samples from animals that were preclinical or of unknown status. However, all of the rapid tests included in our study were able to correctly identify all samples from animals in the clinical stages of disease, apart from samples from animals polymorphic for serine or aspartic acid at codon 146, in which the performance of the Bio-Rad tests was profoundly affected. Our data show that some polymorphisms may adversely affect one test and not another, as well as underline the dangers of extrapolating from other species.

Absence of single nucleotide polymorphisms (SNPs) in the open reading frame (ORF) of the prion protein gene (PRNP) in a large sampling of various chicken breeds

BACKGROUND

Prion diseases are zoonotic diseases with a broad infection spectrum among mammalian hosts and are caused by the misfolded prion protein (PrPSc) derived from the normal prion protein (PrPC), which encodes the prion protein gene (PRNP). Currently, although several prion disease-resistant animals have been reported, a high dose of prion agent inoculation triggers prion disease infection in these disease-resistant animals. However, in chickens, natural prion disease-infected cases have not been reported, and experimental challenges with prion agents have failed to cause infection. Unlike other prion disease-resistant animals, chickens have shown perfect resistance to prion disease thus far. Thus, investigation of the chicken PRNP gene could improve for understanding the mechanism of perfect prion-disease resistance. Here, we investigated the genetic characteristics of the open reading frame (ORF) of the chicken PRNP gene in a large sampling of various chicken breeds.

RESULTS

We found only tandem repeat deletion polymorphisms of the chicken PRNP ORF in the 4 chicken breeds including 106 Dekalb White, 100 Ross, 98 Ogolgye and 100 Korean native chickens. In addition, the distribution of chicken insertion/deletion polymorphisms was significantly different among the 4 chicken breeds. Finally, we found significant differences in the number of PRNP SNPs between prion disease-susceptible species and prion disease-resistant species. Notably, chickens lack SNPs in the ORF of the prion protein.

CONCLUSION

In this study, we found that the absence of SNPs in the chicken PRNP ORF is a notable feature of animals with perfect resistant to prion disease.

The First Report of Polymorphisms and Genetic Features of the prion-like Protein Gene (PRND) in a Prion Disease-Resistant Animal, Dog

Prion disease has displayed large infection host ranges among several species; however, dogs have not been reported to be infected and are considered prion disease-resistant animals. Case-controlled studies in several species, including humans and cattle, indicated a potent association of prion protein gene (PRNP) polymorphisms in the progression of prion disease. Thus, because of the proximal location and similar structure of the PRNP gene among the prion gene family, the prion-like protein gene (PRND) was noted as a novel candidate gene that contributes to prion disease susceptibility. Several case-controlled studies have confirmed the relationship of the PRND gene with prion disease vulnerability, and strong genetic linkage disequilibrium blocks were identified in prion-susceptible species between the PRNP and PRND genes. However, to date, polymorphisms of the dog PRND gene have not been reported, and the genetic linkage between the PRNP and PRND genes has not been examined thus far. Here, we first investigated dog PRND polymorphisms in 207 dog DNA samples using direct DNA sequencing. A total of four novel single nucleotide polymorphisms (SNPs), including one nonsynonymous SNP (c.149G>A, R50H), were identified in this study. We also found two major haplotypes among the four novel SNPs. In addition, we compared the genotype and allele frequencies of the c.149G>A (R50H) SNP and found significantly different distributions among eight dog breeds. Furthermore, we annotated the c.149G>A (R50H) SNP of the dog PRND gene using in silico tools, PolyPhen-2, PROVEAN, and PANTHER. Finally, we examined linkage disequilibrium between the PRNP and PRND genes in dogs. Interestingly, we did not find a strong genetic linkage between these two genes. To the best of our knowledge, this was the first genetic study of the PRND gene in a prion disease-resistant animal, a dog.

Prion-like protein gene (PRND) polymorphisms associated with scrapie susceptibility in Korean native black goats

The polymorphisms of the prion protein (PRNP) gene, which encodes normal prion proteins (PrP), are known to be involved in the susceptibility of prion diseases. The prion-like protein (Doppel) gene (PRND) is the paralog of the PRNP gene and is closely located downstream of the PRNP gene. In addition, the polymorphisms of PRND correlate with disease susceptibility in several animals. We analyzed the genotype and allele frequencies of PRND polymorphisms in 246 Korean native black goats and found a total of six single nucleotide polymorphisms (SNPs) with one novel SNP, c.99C>T. We observed linkage disequilibrium (LD) within and between loci. PRND c.28T>C, c.151A>G, and c.385G>C and PRND c.65C>T and c.286G>A were in perfect LD and we have reported for the first time strong LD between PRND and PRNP or prion-related protein gene (PRNT) loci. Specifically, between the PRND c.28T>C, c.151A>G and c.385G>C and the PRNP codon 143, PRND c.99C>T and the PRNP codon 102 or PRND SNPs (c.28T>C, c.151A>G and c.385G>C) and PRNT SNP (c.321T>C). Furthermore, we confirmed that the genotype distribution of the PRNP p.His143Arg was significantly different according to that of the PRND c.28T>C (P < 0.0001). Finally, using PolyPhen-2 and PROVEAN, we predicted that two non-synonymous SNPs, c.65C>T and c.286G>A, in the PRND gene can have a detrimental effect on Doppel. To the best of our knowledge, this is the first report of genetic characteristics of the PRND gene in Korean native black goats.

The first report of polymorphisms and genetic characteristics of the prion protein gene (PRNP) in horses

Prion diseases have a wide host range, but prion-infected cases have never been reported in horses. Genetic polymorphisms that can directly impact the structural stability of horse prion protein have not been investigated thus far. In addition, we noticed that previous studies focusing on horse-specific amino acids and secondary structure predictions of prion protein were performed for limited parts of the protein. In this study, we found genetic polymorphisms in the horse prion protein gene (PRNP) in 201 Thoroughbred horses. The identified polymorphism was assessed to determine whether this polymorphism impedes stability of protein using PolyPhen-2, PROVEAN and PANTHER. In addition, we evaluated horse-specific amino acids in horse and mouse prion proteins using same methods. We found only one single nucleotide polymorphism (SNP) in the horse prion protein, and three annotation tools predicted that the SNP is benign. In addition, horse-specific amino acids showed different effects on horse and mouse prion proteins, respectively. Abbreviations: PRNP: prion protein gene; SNP: single nucleotide polymorphism; CJD: Creutzfeldt-Jakob disease; CWD: chronic wasting disease; TME: transmissible mink encephalopathy; FSE: feline spongiform encephalopathy; MD: molecular dynamics; ER: endoplasmic reticulum; GPI: glycosylphosphatidylinositol; NMR: nuclear magnetic resonance; ORF: open reading frame; GWAS: genome-wide association study; NAPA: non-adaptive prion amplification; HMM: hidden Markov model; NCBI: National Center for Biotechnology Information.

Goats singly heterozygous for PRNP S146 or K222 orally inoculated with classical scrapie at birth show no disease at ages well beyond 6 years

Scrapie is a transmissible spongiform encephalopathy of sheep and goats, and scrapie eradication programs in many parts of the world rely on strong genetic resistance to classical scrapie in sheep. However, the utility of putative resistance alleles in goats has been a focus of research because goats can transmit scrapie to sheep and may serve as a scrapie reservoir. Prior work showed that disease-free survival time was significantly extended in orally inoculated goats singly heterozygous for prion amino acid substitutions S146 or K222, but average durations were only around 3 years post-inoculation. The aim of this study was to investigate whether extended survival would exceed 6 years, which represents the productive lifetimes of most commercial goats. While all control homozygotes were clinically affected by an average of <2 years, none of the NS146 or QK222 goats developed clinical scrapie or had PrP^Sc-positive rectal biopsies. Several NS146 and QK222 goats developed other conditions unrelated to scrapie, but tissue accumulation of PrP^Sc was not detected in any of these animals. The NS146 heterozygotes have remained disease-free for an average of 2734days (approximately 7.5 years), the longest duration of any classical scrapie challenge experiment with any genotype to date. The QK222 heterozygotes have remained disease-free for an average of 2450days (approximately 6.7 years), the longest reported average duration for QK222 goats challenged with classical scrapie. This research is ongoing, but the current results demonstrate S146 and K222 confer strong resistance to classical scrapie in goats.

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.

Caprine PrP variants harboring Asp-146, His-154 and Gln-211 alleles display reduced convertibility upon interaction with pathogenic murine prion protein in scrapie infected cells

Scrapie, the prion disease of sheep and goats, is a devastating malady of small ruminants. Due to its infectious nature, epidemic outbreaks may occur in flocks/herds consisting of highly susceptible animals. Field studies identified scrapie-protective caprine PrP variants, harboring specific single amino acid changes (Met-142, Arg-143, Asp-146, Ser-146, His-154, Gln-211 and Lys-222). Their effects are under further evaluation, and aim to determine the most protective allele. We assessed some of these variants (Asp-146, His-154, Gln-211 and Lys-222), after their exogenous expression as murine-caprine chimeras in a scrapie- infected murine cell line. We report that exogenously expressed PrPs undergo conformational conversion upon interaction with the endogenous pathological murine prion protein (PrP^SC), which results in the detection of goat-specific and partially PK-resistant moieties. These moieties display a PK-resistance pattern distinct from the one detected in natural goat scrapie cases. Within this cellular model, distinct conformational conversion potentials were assigned to the tested variants. Molecules carrying the Asp-146, His-154 and Gln-211 alleles showed significantly lower conversion levels compared to wild type, confirming their protective effects against scrapie. Although we utilized a heterologous conversion system, this is to our knowledge, the first study of caprine PrP variants in a cellular context of scrapie, that confirms the protective effects of some of the studied alleles.

Effect of Polymorphisms at Codon 146 of the Goat PRNP Gene on Susceptibility to Challenge with Classical Scrapie by Different Routes

This report presents the results of experimental challenges of goats with scrapie by both the intracerebral (i.c.) and oral routes, exploring the effects of polymorphisms at codon 146 of the goat PRNP gene on resistance to disease. The results of these studies illustrate that while goats of all genotypes can be infected by i.c. challenge, the survival distribution of the animals homozygous for asparagine at codon 146 was significantly shorter than those of animals of all other genotypes (chi-square value, 10.8; P = 0.001). In contrast, only those animals homozygous for asparagine at codon 146 (NN animals) succumbed to oral challenge. The results also indicate that any cases of infection in non-NN animals can be detected by the current confirmatory test (immunohistochemistry), although successful detection with the rapid enzyme-linked immunosorbent assay (ELISA) was more variable and dependent on the polymorphism. Together with data from previous studies of goats exposed to infection in the field, these data support the previously reported observations that polymorphisms at this codon have a profound effect on susceptibility to disease. It is concluded that only animals homozygous for asparagine at codon 146 succumb to scrapie under natural conditions.IMPORTANCE In goats, like in sheep, there are PRNP polymorphisms that are associated with susceptibility or resistance to scrapie. However, in contrast to the polymorphisms in sheep, they are more numerous in goats and may be restricted to certain breeds or geographical regions. Therefore, eradication programs must be specifically designed depending on the identification of suitable polymorphisms. An initial analysis of surveillance data suggested that such a polymorphism in Cypriot goats may lie in codon 146. In this study, we demonstrate experimentally that NN animals are highly susceptible after i.c. inoculation. The presence of a D or S residue prolonged incubation periods significantly, and prions were detected in peripheral tissues only in NN animals. In oral challenges, prions were detected only in NN animals, and the presence of a D or S residue at this position conferred resistance to the disease. This study provides an experimental transmission model for assessing the genetic susceptibility of goats to scrapie.

Genetic resistance to transmissible spongiform encephalopathies (TSE) in goats

Breeding programmes to promote resistance to classical scrapie, similar to those for sheep in existing transmissible spongiform encephalopathies (TSE) regulations, have not been established in goats. The European Commission requested a scientific opinion from EFSA on the current knowledge of genetic resistance to TSE in goats. An evaluation tool, which considers both the weight of evidence and strength of resistance to classical scrapie of alleles in the goat PRNP gene, was developed and applied to nine selected alleles of interest. Using the tool, the quality and certainty of the field and experimental data are considered robust enough to conclude that the K222, D146 and S146 alleles both confer genetic resistance against classical scrapie strains known to occur naturally in the EU goat population, with which they have been challenged both experimentally and under field conditions. The weight of evidence for K222 is greater than that currently available for the D146 and S146 alleles and for the ARR allele in sheep in 2001. Breeding for resistance can be an effective tool for controlling classical scrapie in goats and it could be an option available to member states, both at herd and population levels. There is insufficient evidence to assess the impact of K222, D146 and S146 alleles on susceptibility to atypical scrapie and bovine spongiform encephalopathy (BSE), or on health and production traits. These alleles are heterogeneously distributed across the EU Member States and goat breeds, but often at low frequencies (< 10%). Given these low frequencies, high selection pressure may have an adverse effect on genetic diversity so any breeding for resistance programmes should be developed at Member States, rather than EU level and their impact monitored, with particular attention to the potential for any negative impact in rare or small population breeds.

Prion protein gene polymorphisms in Turkish native goat breeds

Susceptibility to 'scrapie' disease in goats is influenced by polymorphisms of the prion protein (PRNP) gene. The aim of this study was to identify PRNP gene polymorphisms in a total of 356 scrapie disease-free goats from 10 Turkish native breeds. Eighteen single-nucleotide polymorphisms were detected in the caprine PRNP open-reading frame. Ten previously described amino acid substitutions (I142M, H143R, N146S, N146D, R151H, R154H, P168Q, R211Q, Q222K and P240S) and two novel dimorphisms (G134E and Q163P) were identified. The strongest association between caprine PRNP and relative resistance to scrapie disease has been reported previously for polymorphisms at codons 146 (S/D) and 222 (K). In the present study, these three PrP variants were relatively rare with 6.3%. This is the first report on PRNP gene variation in Turkish native goat breeds and our knowledge of these polymorphisms will assist goat breeding programmes to reduce the risk of scrapie.

Goats with aspartic acid or serine at codon 146 of the PRNP gene remain scrapie-negative after lifetime exposure in affected herds in Cyprus

The results of the study reported here are part of an ongoing integrated research programme aimed at producing additional, robust, evidence on the genetic resistance to classical scrapie in goats, with particular reference to codon 146. The study targeted animals aged ⩾6 years, which were born and raised in infected herds and were being culled for management reasons. A total of 556 animals were tested, and all positive animals (n = 117) were of the susceptible NN genotype. A total of 246 goats heterozygous or homozygous for putatively resistant alleles (S146 and D146) were screened with no positive results. The outcome of this study supports the hypothesis that the D146 and S146 alleles could be used as the basis for a nationwide strategy for breeding for resistance in the Cypriot goat population.

Review: A review on classical and atypical scrapie in caprine: Prion protein gene polymorphisms and their role in the disease

Scrapie is a naturally occurring transmissible spongiform encephalopathy in sheep and goat. It has been known for ~250 years and is characterised by the accumulation of an abnormal isoform of a host-encoded prion protein that leads to progressive neurodegeneration and death. Scrapie is recognised in two forms, classical and atypical scrapie. The susceptibility to both types of scrapie is influenced by polymorphisms of the prion protein gene (PRNP). Sheep susceptibility or resistance to classical scrapie is strongly regulated by the polymorphisms at codons 136, 154 and 171 of the PRNP. The genetic role in atypical scrapie in sheep has been defined by polymorphisms at codons 141, 154 and 171, which are associated with different degrees of risk in the occurrence of the ovine disease. Progress has been achieved in the prevention of scrapie in sheep due to efficient genetic breeding programmes based on eradication and control of the disease. In Europe, the success of these programmes has been verified by applying eradication and genetic selection plans. In general terms, the ovine selection plans aim to eliminate and reduce the susceptible allele and to enrich the resistant allele ARR. During outbreaks all susceptible animals are slaughtered, only ARR/ARR resistant rams and sheep and semi-resistant females are preserved. In the occurrence of scrapie positive goats a complete cull of the flock (stamping out) is performed with great economic loss and severe risk of extinction for the endangered breeds. The ability to select scrapie-resistant animals allows to define new breeding strategies aimed to boost genetic progress while reducing costs during scrapie outbreaks. Allelic variants of PRNP can be protective for caprine scrapie, and the knowledge of their distribution in goats has become very important. Over the past few years, the integration of genetic information on goat populations could be used to make selection decisions, commonly referred to as genetic selection. The objective of this review was to summarise the main findings of polymorphisms of the caprine prion protein (PrP) gene and to discuss the possible application of goat breeding schemes integrating genetic selection, with their relative advantages and limitations.

Identification of amino acid variation in the prion protein associated with classical scrapie in Canadian dairy goats

BACKGROUND

A clear association of amino acid variation in the prion protein gene (PRNP) with susceptibility and resistance to classical scrapie exists in sheep, but not in goats. In this study we examined DNA sequence variation in the PRNP of 149 animals from two scrapie-infected herds of Saanen dairy goats, and identified 6 non-synonymous variants in the coding region.

RESULTS

In the larger herd, all of the 54 scrapie-affected goats tested had at least one allele with the arginine (R) codon at position 211, with 52 being homozygous for that variant. No animal homozygous for the glutamine (Q) codon at 211 were affected and only two heterozygotes (R/Q) were affected. A weak association was found at position 146 and no significant associations were found with amino acid variation at the remaining four variant positions (142, 143, 222 and 240), however, the allelic variation was low. Similar patterns were observed in the second scrapie-affected herd.

CONCLUSION

We also evaluated previous studies on goat herds affected with scrapie and this relationship of R susceptibility and Q resistance at 211 was present independent of the genotypes at the other positions including 222. The fact that glutamine at 211 provides a significant protective property to scrapie irrespective of the other positions could be important for breeding strategies aimed at improving herd resistance to scrapie, while maintaining important productivity traits.

Variation in the prion protein sequence in Dutch goat breeds

Scrapie is a neurodegenerative disease occurring in goats and sheep. Several haplotypes of the prion protein increase resistance to scrapie infection and may be used in selective breeding to help eradicate scrapie. In this study, frequencies of the allelic variants of the PrP gene are determined for six goat breeds in the Netherlands. Overall frequencies in Dutch goats were determined from 768 brain tissue samples in 2005, 766 in 2008 and 300 in 2012, derived from random sampling for the national scrapie surveillance without knowledge of the breed. Breed specific frequencies were determined in the winter 2013/2014 by sampling 300 breeding animals from the main breeders of the different breeds. Detailed analysis of the scrapie-resistant K222 haplotype was carried out in 2014 for 220 Dutch Toggenburger goats and in 2015 for 942 goats from the Saanen derived White Goat breed. Nine haplotypes were identified in the Dutch breeds. Frequencies for non-wild type haplotypes were generally low. Exception was the K222 haplotype in the Dutch Toggenburger (29%) and the S146 haplotype in the Nubian and Boer breeds (respectively 7 and 31%). The frequency of the K222 haplotype in the Toggenburger was higher than for any other breed reported in literature, while for the White Goat breed it was with 3.1% similar to frequencies of other Saanen or Saanen derived breeds. Further evidence was found for the existence of two M142 haplotypes, M142 /S240 and M142 /P240 . Breeds vary in haplotype frequencies but frequencies of resistant genotypes are generally low and consequently selective breeding for scrapie resistance can only be slow but will benefit from animals identified in this study. The unexpectedly high frequency of the K222 haplotype in the Dutch Toggenburger underlines the need for conservation of rare breeds in order to conserve genetic diversity rare or absent in other breeds.

Prion protein genotype survey confirms low frequency of scrapie-resistant K222 allele in British goat herds

Scrapie in goats is a transmissible, fatal prion disease, which is endemic in the British goat population. The recent success in defining caprine PRNP gene variants that provide resistance to experimental and natural classical scrapie has prompted the authors to conduct a survey of PRNP genotypes in 10 goat breeds and 52 herds to find goats with the resistant K222 allele. They report here the frequencies in 1236 tested animals of the resistance-associated K222 and several other alleles by breed and herd. Eight animals were found to be heterozygous QK222 goats (0.64 per cent genotype frequency, 95 per cent CI 0.28 to 1.27 per cent) but no homozygous KK222 goats were detected. The K222 allele was found in Saanen, Toggenburg and Anglo-Nubian goats. The fact that only a few goats with the K222 allele have been identified does not preclude the possibility to design and implement successful breeding programmes at national level.