Apolipoprotein E is immunochemically localized to the senile plaques, vascular amyloid, and neurofibrillary tangles of Alzheimer disease. In vitro, apolipoprotein E in cerebrospinal fluid binds to synthetic beta A4 peptide (the primary constituent of the senile plaque) with high avidity. Amino acids 12-28 of the beta A4 peptide are required. The gene for apolipoprotein E is located on chromosome 19q13.2, within the region previously associated with linkage of late-onset familial Alzheimer disease. Analysis of apolipoprotein E alleles in Alzheimer disease and controls demonstrated that there was a highly significant association of apolipoprotein E type 4 allele (APOE-epsilon 4) and late-onset familial Alzheimer disease. The allele frequency of the APOE-epsilon 4 in 30 random affected patients, each from a different Alzheimer disease family, was 0.50 +/- 0.06; the allele frequency of APOE-epsilon 4 in 91 age-matched unrelated controls was 0.16 +/- 0.03 (Z = 2.44, P = 0.014). A functional role of the apolipoprotein E-E4 isoform in the pathogenesis of late-onset familial Alzheimer disease is suggested.

https://www.pnas.org/content/pnas/90/5/1977.full.pdf

Apolipoprotein E: high-avidity binding to beta-amyloid and increased frequency of type 4 allele in late-onset familial Alzheimer disease.

The fundamental event in prion diseases seems to be a conformational change in cellular prion protein (PrPC) whereby it is converted into the pathologic isoform PrPSc. In fatal familial insomnia (FFI), the protease-resistant fragment of PrPSc after deglycosylation has a size of 19 kilodaltons, whereas that from other inherited and sporadic prion diseases is 21 kilodaltons. Extracts from the brains of FFI patients transmitted disease to transgenic mice expressing a chimeric human-mouse PrP gene about 200 days after inoculation and induced formation of the 19-kilodalton PrPSc fragment, whereas extracts from the brains of familial and sporadic Creutzfeldt-Jakob disease patients produced the 21-kilodalton PrPSc fragment in these mice. The results presented indicate that the conformation of PrPSc functions as a template in directing the formation of nascent PrPSc and suggest a mechanism to explain strains of prions where diversity is encrypted in the conformation of PrPSc.

https://science.sciencemag.org/content/sci/274/5295/2079.full.pdf

Evidence for the Conformation of the Pathologic Isoform of the Prion Protein Enciphering and Propagating Prion Diversity

We sequenced the prion protein gene and studied the biochemical characteristics and the intracerebral distribution of protease-resistant prion protein with Western blot and immunohistochemistry in 19 cases of sporadic Creutzfeldt-Jakob disease. We identified four groups of subjects defined by the genotype at codon 129 of the prion protein gene, the site of a common methionine/valine polymorphism, and two types of protease-resistant prion proteins that differed in size and glycosylation. The four Creutzfeldt-Jakob disease groups showed distinct clinicopathological features that corresponded to previously described variants. The typical Creutzfeldt-Jakob disease phenotype or myoclonic variant and the Heidenhain variant were linked to methionine homozygosity at codon 129 and to "type 1" protease-resistant prion protein. The atypical and rarer variants such as that with dementia of long duration, the ataxic variant, and the variant with kuru plaques were linked to different genotypes at codon 129 and shared the "type 2" protease-resistant prion protein. Our data indicate that the sporadic form of Creutzfeldt-Jakob disease comprises a limited number of variants. The methionine/valine polymorphism at codon 129 of the prion protein gene and two types of protease-resistant prion proteins are the major determinants of these variants. These findings suggest the existence of prion strains in humans and provide the molecular basis for a novel classification of sporadic Creutzfeldt-Jakob disease.

Molecular basis of phenotypic variability in sporadic Creutzfeldt-Jakob disease.

We present a synthesis of clinical, neuropathological, and biological details of the National Institutes of Health series of 300 experimentally transmitted cases of spongiform encephalopathy from among more than 1,000 cases of various neurological disorders inoculated into nonhuman primates during the past 30 years. The series comprises 278 subjects with Creutzfeldt-Jakob disease, of whom 234 had sporadic, 36 familial, and 8 iatrogenic disease; 18 patients with kuru; and 4 patients with Gerstmann-Strussler-Scheinker syndrome. Sporadic Creutzfeldt-Jakob disease, numerically by far the most important representative, showed an average age at onset of 60 years, with the frequent early appearance of cerebellar and visual/oculomotor signs, and a broad spectrum of clinical features during the subsequent course of illness, which was usually fatal in less than 6 months. Characteristic spongiform neuropathology was present in all but 2 subjects. Microscopically visible kuru-type amyloid plaques were found in 5% of patients with Creutzfeldt-Jakob disease, 75% of those with kuru, and 100% of those with Gerstmann-Straussler-Scheinker syndrome; brain biopsy was diagnostic in 95% of cases later confirmed at autopsy, and proteinase-resistant amyloid protein was identified in Western blots of brain extracts from 88% of tested subjects. Experimental transmission rates were highest for iatrogenic Creutzfeldt-Jakob disease (100%), kuru (95%), and sporadic Creutzfeldt-Jakob disease (90%), and considerably lower for most familial forms of disease (68%). Incubation periods as well as the durations and character of illness showed great variability, even in animals receiving the same inoculum, mirroring the spectrum of clinical profiles seen in human disease. Infectivity reached average levels of nearly 10(5) median lethal doses/gm of brain tissue, but was only irregularly present (and at much lower levels) in tissues outside the brain, and, except for cerebrospinal fluid, was never detected in bodily secretions or excretions.

Human spongiform encephalopathy: the National Institutes of Health series of 300 cases of experimentally transmitted disease

The molecular basis of strain variation in scrapie diseases is unknown. The only identified component of the agent is the posttranslationally modified host prion protein (PrPSc). The biochemical and physical properties of PrP from two strains of transmissible mink encephalopathy (TME), called hyper (HY) and drowsy (DY), were compared to investigate if PrP heterogeneity could account for strain diversity. The degradation rate of PrPTME digested with proteinase K was found to be strain specific and correlated with inactivation of the TME titer. Edman protein sequencing revealed that the major N-terminal end of HY PrPTME commenced at least 10 amino acid residues prior to that of DY PrPTME after digestion with proteinase K. Analysis of the brain distribution of PrPTME exhibited a strain-specific pattern and localization of PrPTME to the perikarya of specific neuron populations. Our findings are consistent with HY and DY PrPTME having distinct protein conformations and/or strain-specific ligand interactions that influence PrPTME properties. We propose that PrPTME conformation could play a role in targeting TME strains to different neuron populations in which strain-specific formation occurs. These data are consistent with the idea that PrPTME protein structure determines the molecular basis of strain variation. Images

Distinct PrP properties suggest the molecular basis of strain variation in transmissible mink encephalopathy.

Fatal familial insomnia (FFI) and a subtype of familial Creutzfeldt-Jakob disease (CJD), two clinically and pathologically distinct diseases, are linked to the same mutation at codon 178 (Asn178) of the prion protein gene. The possibility that a second genetic component modified the phenotypic expression of the Asn178 mutation was investigated. FFI and the familial CJD subtype segregated with different genotypes determined by the Asn178 mutation and the methionine-valine polymorphism at codon 129. The Met129, Asn178 allele segregated with FFI in all 15 affected members of five kindreds whereas the Val129, Asn178 allele segregated with the familial CJD subtype in all 15 affected members of six kindreds. Thus, two distinct disease phenotypes linked to a single pathogenic mutation can be determined by a common polymorphism.

https://science.sciencemag.org/content/sci/258/5083/806.full.pdf

William W. Pendelbury

Papers

Fatal familial insomnia and familial Creutzfeldt-Jakob disease: disease phenotype determined by a DNA polymorphism