Brian S. Appleby

Rapidly progressive Alzheimer's disease features distinct structures of amyloid-β.

Genetic and environmental factors that increase the risk of late-onset Alzheimer disease are now well recognized but the cause of variable progression rates and phenotypes of sporadic Alzheimers disease is largely unknown. We aimed to investigate the relationship between diverse structural assemblies of amyloid-β and rates of clinical decline in Alzheimers disease. Using novel biophysical methods, we analysed levels, particle size, and conformational characteristics of amyloid-β in the posterior cingulate cortex, hippocampus and cerebellum of 48 cases of Alzheimers disease with distinctly different disease durations, and correlated the data with APOE gene polymorphism. In both hippocampus and posterior cingulate cortex we identified an extensive array of distinct amyloid-β42 particles that differ in size, display of N-terminal and C-terminal domains, and conformational stability. In contrast, amyloid-β40 present at low levels did not form a major particle with discernible size, and both N-terminal and C- terminal domains were largely exposed. Rapidly progressive Alzheimers disease that is associated with a low frequency of APOE e4 allele demonstrates considerably expanded conformational heterogeneity of amyloid-β42, with higher levels of distinctly structured amyloid-β42 particles composed of 30-100 monomers, and fewer particles composed of < 30 monomers. The link between rapid clinical decline and levels of amyloid-β42 with distinct structural characteristics suggests that different conformers may play an important role in the pathogenesis of distinct Alzheimers disease phenotypes. These findings indicate that Alzheimers disease exhibits a wide spectrum of amyloid-β42 structural states and imply the existence of prion-like conformational strains.

Diagnostic and prognostic value of human prion detection in cerebrospinal fluid

Several prion amplification systems have been proposed for detection of prions in cerebrospinal fluid (CSF), most recently, the measurements of prion seeding activity with second‐generation real‐time quaking‐induced conversion (RT‐QuIC). The objective of this study was to investigate the diagnostic performance of the RT‐QuIC prion test in the broad phenotypic spectrum of prion diseases.

Gerstmann-Sträussler-Scheinker disease subtypes efficiently transmit in bank voles as genuine prion diseases.

Gerstmann-Sträussler-Scheinker disease (GSS) is an inherited neurodegenerative disorder associated with mutations in the prion protein gene and accumulation of misfolded PrP with protease-resistant fragments (PrPres) of 6–8 kDa. With the exception of a few GSS cases characterized by co-accumulation of PrPres of 21 kDa, efforts to transmit GSS to rodents have been unsuccessful. As a result, GSS subtypes exclusively associated with 6–8 kDa PrPres have often been considered as non-transmissible proteinopathies rather than true prion diseases. We show that GSS with P102L, A117V and F198S mutations transmit efficiently and produce distinct pathological phenotypes in bank voles (M. glareolus), irrespective of the presence of 21 kDa PrPres in the inoculum, demonstrating that GSS is a genuine prion disease characterized by both transmissibility and strain variation.

Distinct prion-like strains of amyloid beta implicated in phenotypic diversity of Alzheimer’s disease

ABSTRACT Vast evidence on human prions demonstrates that variable disease phenotypes, rates of propagation, and targeting of distinct brain structures are determined by unique conformers (strains) of pathogenic prion protein (PrPSc). Recent progress in the development of advanced biophysical tools that inventory structural characteristics of amyloid beta (Aβ) in the brain cortex of phenotypically diverse Alzheimers disease (AD) patients, revealed unique spectrum of oligomeric particles in the cortex of rapidly progressive cases, implicating these structures in variable rates of propagation in the brain, and in distict disease manifestation. Since only ∼30% of phenotypic diversity of AD can be explained by polymorphisms in risk genes, these and transgenic bioassay data argue that structurally distinct Aβ particles play a major role in the diverse pathogenesis of AD, and may behave as distinct prion-like strains encoding diverse phenotypes. From these observations and our growing understanding of prions, there is a critical need for new strain-specific diagnostic strategies for misfolded proteins causing these elusive disorders. Since targeted drug therapy can induce mutation and evolution of prions into new strains, effective treatments of AD will require drugs that enhance clearance of pathogenic conformers, reduce the precursor protein, or inhibit the conversion of precursors into prion-like states.

Prion seeding activity and infectivity in skin samples from patients with sporadic Creutzfeldt-Jakob disease

Infectious prions can be detected in the skin of patients with sporadic Creutzfeldt-Jakob disease. Prions in unexpected places Sporadic Creutzfeldt-Jakob disease (sCJD), the most common human prion disease, can be transmitted via neurosurgical instruments or corneal or dura mater transplants contaminated by infectious prions. Some epidemiological studies have associated sCJD risk with surgeries that involve the skin, but whether the skin of sCJD patients contains prion infectivity is not known. Orrú et al. now report detectable prion seeding activity and infectivity in skin from sCJD patients, although at much lower levels compared to brain tissues from sCJD patients. These data suggest that there may be a potential for iatrogenic sCJD transmission through skin. Sporadic Creutzfeldt-Jakob disease (sCJD), the most common human prion disease, is transmissible through iatrogenic routes due to abundant infectious prions [misfolded forms of the prion protein (PrPSc)] in the central nervous system (CNS). Some epidemiological studies have associated sCJD risk with non-CNS surgeries. We explored the potential prion seeding activity and infectivity of skin from sCJD patients. Autopsy or biopsy skin samples from 38 patients [21 sCJD, 2 variant CJD (vCJD), and 15 non-CJD] were analyzed by Western blotting and real-time quaking-induced conversion (RT-QuIC) for PrPSc. Skin samples from two patients were further examined for prion infectivity by bioassay using two lines of humanized transgenic mice. Western blotting revealed dermal PrPSc in one of five deceased sCJD patients and one of two vCJD patients. However, the more sensitive RT-QuIC assay detected prion seeding activity in skin from all 23 CJD decedents but not in skin from any non-CJD control individuals (with other neurological conditions or other diseases) during blinded testing. Although sCJD patient skin contained ~103- to 105-fold lower prion seeding activity than did sCJD patient brain tissue, all 12 mice from two transgenic mouse lines inoculated with sCJD skin homogenates from two sCJD patients succumbed to prion disease within 564 days after inoculation. Our study demonstrates that the skin of sCJD patients contains both prion seeding activity and infectivity, which raises concerns about the potential for iatrogenic sCJD transmission via skin.

Caregiver burden in atypical dementias: comparing frontotemporal dementia, Creutzfeldt-Jakob disease, and Alzheimer's disease.

BACKGROUND Caregiver burden is a significant issue in the treatment of dementia and a known contributor to institutionalization of patients with dementia. Published data have documented increased caregiver burden in behavioral variant frontotemporal dementia (bvFTD) compared to Alzheimers disease (AD). Another atypical dementia with high-perceived caregiver burden is sporadic Creutzfeldt-Jakob disease (sCJD), but no formal studies have assessed this perception. The aim of this study was to compare caregiver burden across atypical dementia etiologies. METHODS 76 adults with atypical dementia (young-onset AD [YOAD], bvFTD, language variant FTD [lvFTD], and sCJD) were administered an abbreviated version of the Zarit Burden Interview (ZBI), Neuropsychiatric Inventory (NPI-Q), and other assessment instruments during a five-year time period at Johns Hopkins Hospital (JHH). A Cox regression model examined differences between disease categories that impact mean ZBI scores. RESULTS Mean ZBI scores were significantly different between dementia etiologies, with bvFTD and sCJD having the highest caregiver burden (p = 0.026). Mean NPI-Q caregiver distress scores were highest in bvFTD and sCJD (p = 0.002), with sCJD and bvFTD also having the highest number of endorsed symptom domains (p = 0.012). On regression analyses, an interactive variable combining final diagnosis category and NPI-Q total severity score demonstrated statistically significant differences in mean ZBI scores for sCJD and bvFTD. CONCLUSIONS This study demonstrates that bvFTD and sCJD have increased levels of caregiver burden, NPI-Q caregiver distress, total severity scores, and number of endorsed symptom domains. These results suggest that higher caregiver burden in bvFTD and sCJD are disease specific and possibly related to neuropsychiatric symptoms.

Rapidly Progressive Young-Onset Dementias: Neuropsychiatric Aspects

Rapidly progressive dementia (RPD) is roughly defined as neurocognitive decline resulting in dementia or death within 2 years. Although RPDs affect all age groups, many occur in patients with young-onset dementia. Although prion disease (eg, Creutzfeldt-Jakob disease) is often thought to be the prototypic rapidly progressive young-onset dementia, the differential diagnosis is broad and some etiologies may be treatable. Hence, an appropriate workup to determine the etiology of RPD is crucial to planning the appropriate management. This article reviews the differential diagnosis, diagnostic workup, and management considerations for this unique patient population.

Initial Diagnoses of Patients Ultimately Diagnosed with Prion Disease

BACKGROUND Prion diseases are rapidly progressive neurodegenerative diseases that frequently mimic other forms of dementia making them difficult to diagnose. OBJECTIVE To explore factors associated with the initial diagnoses of cases later determined to be caused by prion disease in an attempt to recognize key clinical variables that impact the timely diagnosis of prion disease. METHODS A retrospective chart review performed at Johns Hopkins Medicine and the Department of Veterans Affairs Health Care System (1995-2008) was conducted. Ninety-two subjects with definite or probable prion disease were included in the analyses. Demographic, clinical, diagnostic test results, neuropathologic, molecular, and genetic data were collected using a standardized instrument and compared between initial diagnosis groups. RESULTS Cases were separated into five broad categories pertaining to their initial diagnoses: prion disease, non-prion-related dementia, psychiatric disorder, stroke, and other. The majority of cases did not receive an initial diagnosis of prion disease (n = 76, 83%). The plurality of subjects received an initial diagnosis of a non-prion disease related dementia (n = 33, 36%). Mean survival times varied between initial diagnosis groups (p = 0.042). Times to cerebrospinal fluid 14-3-3 analysis and electroencephalogram also differed between initial diagnosis groups. CONCLUSIONS Most patients with prion disease are initially diagnosed with a non-prion disease related dementia. Several clinical features were associated with initial diagnoses including survival time, onset of specific symptoms, and times to 14-3-3 analyses and electroencephalogram. Expanding our knowledge of the various clinical presentations of prion disease, especially dementia, may aid in the earlier diagnoses of these rapidly progressive diseases.

Fluorodeoxyglucose Positron Emission Tomography (FDG-PET) Correlation of Histopathology and MRI in Prion Disease

Creutzfeldt-Jakob disease (CJD) and other prion diseases are rapidly progressive spongiform encephalopathies that are invariably fatal. Clinical features and magnetic resonance imaging, electroencephalogram, and cerebrospinal fluid abnormalities may suggest prion disease, but a definitive diagnosis can only be made by means of neuropathologic examination. Fluorodeoxyglucose positron emission tomography (FDG-PET) is not routinely used to evaluate patients with suspected prion disease. This study includes 11 cases of definite prion disease in which FDG-PET scans were obtained. There were 8 sporadic CJD cases, 2 genetic CJD cases, and 1 fatal familial insomnia case. Automated FDG-PET analysis revealed parietal region hypometabolism in all cases. Surprisingly, limbic and mesolimbic hypermetabolism were also present in the majority of cases. When FDG-PET hypometabolism was compared with neuropathologic changes (neuronal loss, astrocytosis, spongiosis), hypometabolism was predictive of neuropathology in 80.6% of cortical regions versus 17.6% of subcortical regions. The odds of neuropathologic changes were 2.1 times higher in cortical regions than subcortical regions (P=0.0265). A similar discordance between cortical and subcortical regions was observed between FDG-PET hypometabolism and magnetic resonance imaging diffusion weighted imaging hyperintensity. This study shows that there may be a relationship between FDG-PET hypometabolism and neuropathology in cortical regions in prion disease but it is unlikely to be helpful for diagnosis.

Novel strain properties distinguishing sporadic prion diseases sharing prion protein genotype and prion type

In most human sporadic prion diseases the phenotype is consistently associated with specific pairings of the genotype at codon 129 of the prion protein gene and conformational properties of the scrapie PrP (PrPSc) grossly identified types 1 and 2. This association suggests that the 129 genotype favours the selection of a distinct strain that in turn determines the phenotype. However, this mechanism cannot play a role in the phenotype determination of sporadic fatal insomnia (sFI) and a subtype of sporadic Creutzfeldt-Jakob disease (sCJD) identified as sCJDMM2, which share 129 MM genotype and PrPSc type 2 but are associated with quite distinct phenotypes. Our detailed comparative study of the PrPSc conformers has revealed major differences between the two diseases, which preferentially involve the PrPSc component that is sensitive to digestion with proteases (senPrPSc) and to a lesser extent the resistant component (resPrPSc). We conclude that these variations are consistent with two distinct strains in sFI and sCJDMM2, and that the rarer sFI is the result of a variant strain selection pathway that might be favoured by a different brain site of initial PrPSc formation in the two diseases.