A rapid and efficient method for the detection of point mutations of the human prion protein gene (PRNP) by direct sequencing

Polymorphism of prion protein gene in sheep of Inner Mongolian, China

Susceptibility to natural scrapie in sheep is associated with polymorphisms at codons 136, 154 and 171 of the prion protein (PrP) gene. To assess the risk of scrapie in sheep raised in China, DNA from 30 sheep of two breeds was isolated, amplified and sequenced for the PrP gene. The ovine PrP gene was found to be highly homogenous. The genotype associated with high susceptibility to scrapie (VRQ) was absent, whereas that associated with the resistance (ARR) was present in 6.7% of sheep examined. ARK was also rare (6.7%). ARQ that is associated with an intermediate susceptibility was the genotype observed in the most of sheep examined (86.6%). These data suggest that Chinese sheep of Mongolian sheep breed are susceptible to scrapie.

Reference materials for the evaluation of pre-mortem variant Creutzfeldt-Jakob disease diagnostic assays

BACKGROUND AND OBJECTIVES

A standard panel of materials is needed for the evaluation of assays being developed for the diagnosis of variant Creutzfeldt-Jakob disease.

MATERIALS AND METHODS

Tissues from human and animals incubating transmissible spongiform encephalopathy disease have been prepared, aliquoted and where possible characterized by in vitro methods.

RESULTS

A standardized preparation of materials has been generated.

CONCLUSIONS

Large-scale preparations of tissues and blood fractions can be used to directly compare the sensitivities of assays using different formats.

Prion protein gene M129 allele is a risk factor for Alzheimer's disease

Prion protein gene polymorphism M129V represents a known risk factor for Creutzfeldt-Jakob disease. Recently, the meta-analysis revealed that homozygosity at codon 129 is connected with increased risk of Alzheimer's disease (AD). To determine whether M129V polymorphism is a risk factor for AD we analyzed a group of early-onset, and late-onset Polish AD patients. We observed that in LOAD patients there is a statistically significant increase of MM (p=0.0028) and decrease of MV (p=0.0006) genotype frequency, as compared to controls. When both groups were stratified according to APOE4 status, increase of MM and decrease of MV genotype frequency were significant in the LOAD subgroup with no APOE4 (p=0.017, and p=0.018, respectively). In the subgroup with APOE4 allele, only MV genotype frequency was significantly lower, as compared to controls (p=0.035). However, no interaction was found between APOE4 status and M129V polymorphism. We conclude that MM genotype increases LOAD risk in Polish population independently from the APOE4 status.

Safety characterization of HeLa-based cell substrates used in the manufacture of a recombinant adeno-associated virus-HIV vaccine

The use of transformed cell substrates for prophylactic vaccine manufacturing is widely debated. Extensive characterization is required to address the suitability of neoplastic cell substrates for vaccine manufacture. The HeLa-based cell substrate used in the manufacture of a prophylactic rAAV-HIV vaccine, AAV2-gagPR delta RT (tgAAC09) was tested in vivo for its tumor-forming potential, the oncogenic potential of its high molecular weight DNA and the potential presence of occult oncogenic adventitious agents. This data from these in vivo studies, in conjunction with prion gene and protein characterization, cell and viral clearance studies and quantity of residual host-cell DNA levels in the purified tgAAC09 vaccine, were used to establish what we believe to be an acceptable safety profile for the vaccine manufacturing process. The tumor-producing dose in 50% of the animals was consistent with that in a published report from FDA staff for HeLa cells. High molecular weight cellular DNA was not oncogenic and no occult oncogenic agents were detected by testing in nude mice and newborn rodent models, respectively. Endogenous prion protein was also normal and genomic sequence analysis detected no mutations associated with increased risk of prion disease. In addition, the purification process used to produce this vaccine candidate removed all detectable cells (clearance of greater than 22 log10), viral clearance study showed 6-17 log10 clearance of three model viruses and host-cell DNA in the bulk product was less than 100pg host-cell DNA per dose of 3 x 10(11) DNase resistant particles (DRP) of the vaccine. Taken together, the data from the in vivo and in vitro tests that were performed to characterize the HeLa based producer cell line (T3B12-5B) and HeLa S3 cells support the use of these cells as substrates for the manufacture of a purified rAAV-HIV vaccine candidate. The data also supports the ability of the process, employing the HeLa cell substrate, used to manufacture the rAAV-HIV vaccine to produce a product as free of adventitious agents as current testing procedures can document. Safety of the rAAV-HIV vaccine is currently being assessed in a Phase I clinical trial.

Variation of the prion gene in chimpanzees and its implication for prion diseases

In humans, familial prion diseases are linked to mutations in the PRNP gene. We have sequenced part of this gene in a large sample of common chimpanzee, Pan troglodytes (n=130 chromosomes). No variation in codons 129 and 219 has been observed: all chimpanzees were homozygous for the Met allele, which in humans increases susceptibility to Creutzfeldt-Jakob disease. We found two sequence variants: one is a synonymous polymorphism unique to the chimpanzee at codon 226, TAC to TAT (Y), with a TAC allele frequency of 80.6%; the other is a non-synonymous change at codon 148 (R148H) that falls in the target epitope for some common commercial antibodies used for prion diagnostics, and is highly conserved across species. The pathogenicity of this mutation is still unknown.

Prospects for the development of pre-mortem laboratory diagnostic tests for Creutzfeldt-Jakob disease

At present the diagnosis of Creutzfeldt-Jakob disease (CJD) and related transmissible spongiform encephalopathies in humans is based on clinical criteria and (at post-mortem) the histopathological and immunological examination of brain tissue. The misfolded prion protein, PrPSc, is the single most significant marker, but its recognition by standard serological methods is complicated by its antigenic similarity to the normal prion protein, PrPC. Although there are commercial diagnostic assays available for bovine spongiform encephalopathy using brain specimens taken at slaughter, there are no suitable pre-mortem assays for cattle and none either for pre-mortem human disease. Especially in view of the recent report of variant CJD transmission by blood transfusion, it is important that tests for pre-symptomatic infections are developed. This will safeguard the blood supply and, for example, prevent the transmission of CJD in neurosurgery. This paper reviews the current and prospective approaches to the pre-mortem diagnosis of CJD, in particular its variant form.

Rapid detection of the prion protein M129V polymorphism with the LightCycler

The common single nucleotide polymorphism at codon 129 of the prion protein gene is a key determinant of the genetic susceptibility to Creutzfeldt-Jakob disease (CJD). Recently, a molecular classification of sporadic CJD based on the M129V genotype in conjunction with other determinants was proposed. In the present study, we describe the development and evaluation of a rapid fluorescent-based assay to detect this polymorphism using the LightCycler system. The two polymorphic alleles could be clearly distinguished by their melting points at 52.1 and 60.4 degrees C, representing the 129V and 129M alleles, respectively. These results were confirmed by DNA sequencing. We evaluated our test in 400 patient samples and found no deviations from the expected melting patterns. The calculated allele frequency for the M-allele was 0.66. Thus, we have established a rapid, reliable fluorescent assay for high-throughput detection of the prion protein M129V polymorphism.

Mutation of the PRNP gene at codon 211 in familial Creutzfeldt-Jakob disease

Creutzfeldt-Jakob disease (CJD) belongs to a group of chronic, progressive, neurodegenerative disorders that may be hereditary, infectious, or sporadic. Hereditary CJDs are associated with mutations in the PRNP gene on chromosome 20p12-pter. We report a family in which four patients developed classical clinical signs of CJD, including severe cognitive decline, cerebellar signs, myoclonic jerks, and synchronic periodic discharges on electroencephalogram. The E211Q mutation has been identified in family members, but not in 97 sporadic CJD patients referred to the Italian registry of CJD nor in 205 healthy normal subjects, suggesting a pathogenic role for this mutation.