Ana Lukic

Tau, prions and Aβ: the triad of neurodegeneration

This article highlights the features that connect prion diseases with other cerebral amyloidoses and how these relate to neurodegeneration, with focus on tau phosphorylation. It also discusses similarities between prion disease and Alzheimer’s disease: mechanisms of amyloid formation, neurotoxicity, pathways involved in triggering tau phosphorylation, links to cell cycle pathways and neuronal apoptosis. We review previous evidence of prion diseases triggering hyperphosphorylation of tau, and complement these findings with cases from our collection of genetic, sporadic and transmitted forms of prion diseases. This includes the novel finding that tau phosphorylation consistently occurs in sporadic CJD, in the absence of amyloid plaques.

The Medical Research Council Prion Disease Rating Scale: a new outcome measure for prion disease therapeutic trials developed and validated using systematic observational studies

Progress in therapeutics for rare disorders like prion disease is impeded by the lack of validated outcome measures and a paucity of natural history data derived from prospective observational studies. The first analysis of the U.K. National Prion Monitoring Cohort involved 1337 scheduled clinical assessments and 479 telephone assessments in 437 participants over 373 patient-years of follow-up. Scale development has included semi-quantitative and qualitative carer interviews, item response modelling (Rasch analysis), inter-rater reliability testing, construct analysis and correlation with several existing scales. The proposed 20-point Medical Research Council prion disease rating scale assesses domains of cognitive function, speech, mobility, personal care/feeding and continence, according to their relative importance documented by carer interviews. It is quick and simple to administer, and has been validated for use by doctors and nurses and for use over the telephone, allowing for frequent assessments that capture the rapid change typical of these diseases. The Medical Research Council Scale correlates highly with widely used cognitive and single item scales, but has substantial advantages over these including minimal floor effects. Three clear patterns of decline were observed using the scale: fast linear decline, slow linear decline (usually inherited prion disease) and in some patients, decline followed by a prolonged preterminal plateau at very low functional levels. Rates of decline and progress through milestones measured using the scale vary between sporadic, acquired and inherited prion diseases following clinical expectations. We have developed and validated a new functionally-oriented outcome measure and propose that future clinical trials in prion disease should collect data compatible with this scale, to allow for combined and comparative analyses. Such approaches may be advantageous in orphan conditions, where single studies of feasible duration will often struggle to achieve statistical power.

MRI findings are often missed in the diagnosis of Creutzfeldt-Jakob disease

BackgroundEstablishing a confident clinical diagnosis before an advanced stage of illness can be difficult in Creutzfeldt-Jakob disease (CJD) but unlike common causes of dementia, prion diseases can often be diagnosed by identifying characteristic MRI signal changes. However, it is not known how often CJD-associated MRI changes are identified at the initial imaging report, whether the most sensitive sequences are used, and what impact MRI-diagnosis has on prompt referral to clinical trial-like studies.MethodsWe reviewed the MRI scans of 103 patients with CJD referred to the National Prion Clinic since 2007 and reviewed the presence of CJD-associated changes, compared these findings with the formal report from the referring centre and reviewed the types of sequence performed.ResultsIn sCJD we found CJD-associated MRI changes in 83 of 91 cases (91% sensitivity). However, the referring centres documented CJD-associated MRI changes in 43 of the sCJD cases (47% sensitivity). The most common region not documented by referring centres was the cortex (23 of 68 sCJD cases), but there was a statistically significant discrepancy in all regions (p<0.0001). Patients in whom MRI abnormalities were missed by the referring hospital were more advanced at the time of recruitment to a clinical trial-like study (p=0.03).ConclusionsCJD-associated MRI changes are often not documented on the formal investigation report at the referring centre. This is important as delay makes enrolment to clinical trials futile because of highly advanced disease. If a diagnosis of CJD is suspected, even if the initial imaging is reported as normal, a specialist MRI review either by an experienced neuroradiologist or by a prion disease specialist unit could facilitate earlier diagnosis.

Heterozygosity at Polymorphic Codon 219 in Variant Creutzfeldt-Jakob Disease

BACKGROUNDnGenetic variants of the prion protein gene (PRNP) strongly determine susceptibility to prion diseases. All tested patients with definite variant Creutzfeldt-Jakob disease (vCJD) are homozygous for methionine at a common polymorphism at codon 129. A further genetic polymorphism at codon 219, a common variant in several Asian populations, is considered protective against sporadic CJD.nnnOBJECTIVEnTo report a finding of heterozygosity at codon 219 in 2 patients with vCJD.nnnDESIGNnCase reports.nnnSETTINGnMRC (Medical Research Council) Prion Unit and Department of Neurodegenerative Disease, University College London Institute of Neurology, and National Prion Clinic, National Hospital for Neurology and Neurosurgery. Patients Two patients with clinical and investigation findings consistent with the diagnoses of probable vCJD.nnnMAIN OUTCOME MEASURESnClinical and genetic findings.nnnRESULTSnA 34-year-old man had a 15-month history of behavioral change progressing to ataxia, dysarthria, involuntary choreiform movements, and severe cognitive impairment. Cerebrospinal fluid analysis was positive for 14-3-3 protein, electroencephalography showed generalized slowing, and magnetic resonance imaging revealed thalamic high signal bilaterally, typical of vCJD. A 31-year-old woman had a 16-month history of cognitive decline, ataxia, involuntary choreiform movements, and myoclonic jerks. Magnetic resonance imaging showed bilateral pulvinar high signal. The diagnosis was confirmed by a tonsillar biopsy demonstrating abnormal prion protein deposition in a typical pattern for vCJD. PRNP sequencing showed a methionine homozygous codon 129 genotype and an E219K polymorphism in both patients.nnnCONCLUSIONSnThe E219K polymorphism is neutral or may even confer susceptibility to vCJD. The observations are interpretable in the context of the conformational selection model of prion replication. A barrier to prion disease transmission depends on the degree to which permitted pathologic conformations of the prion protein overlap between the inoculum and the host.

Behavioral and Psychiatric Symptoms in Prion Disease

The prion diseases are rare neurodegenerative conditions that cause complex and highly variable neuropsychiatric syndromes, often with remarkably rapid progression. Prominent behavioral and psychiatric symptoms have been recognized since these diseases were first described. While research on such symptoms in common dementias has led to major changes in the way these symptoms are managed, evidence to guide the care of patients with prion disease is scarce. The authors review the published research and draw on more than 10 years experience at the U.K. National Prion Clinic, including two large prospective clinical research studies in which more than 300 patients with prion disease have been followed up from diagnosis to death, with detailed observational data gathered on symptomatology and symptomatic treatments. The authors group behavioral and psychiatric symptoms into psychotic features, agitated features, and mood disorder and describe their natural history, showing that they spontaneously improve or resolve in many patients and are short-lived in many others because of rapid progression of global neurological disability. Diagnostic category, disease severity, age, gender, and genetic variation are or may be predictive factors. The authors review the observational data on pharmacological treatment of these symptoms in the U.K. clinical studies and make cautious recommendations for clinical practice. While nonpharmacological measures should be the first-line interventions for these symptoms, the authors conclude that there is a role for judicious use of pharmacological agents in some patients: antipsychotics for severe psychosis or agitation; benzodiazepines, particularly in the late stages of disease; and antidepressants for mood disorder.

The cognitive profile of prion disease: a prospective clinical and imaging study

Prion diseases are dementing illnesses with poorly defined neuropsychological features. This is probably because the most common form, sporadic Creutzfeldt‐Jakob disease, is often rapidly progressive with pervasive cognitive decline making detailed neuropsychological investigation difficult. This study, which includes patients with inherited, acquired (iatrogenic and variant) and sporadic forms of the disease, is the only large‐scale neuropsychological investigation of this patient group ever undertaken and aimed to define a neuropsychological profile of human prion diseases.

Familial Alzheimer's disease and inherited prion disease in the UK are poorly ascertained

Aims To ascertain the frequency and geographical distribution of patients diagnosed with known genetic causes of Alzheimers disease (AD) and inherited prion disease (IPD) in the UK 2001–2005. By comparison with frequencies predicted from published population studies, to estimate the proportion of patients with these conditions who are being accurately diagnosed. Methods All the positive diagnostic test results (from both genetic testing centres) were identified for mutations in presenilin-1 (PSEN1), presenilin-2 (PSEN2), amyloid precursor protein (APP) and prion protein genes (PRNP) for patients resident in the UK in a 5 year period. The variation in the incidence of mutation detection between UK regions was assessed with census population data. Published studies of the genetic epidemiology of familial early onset AD (EOAD) were reviewed to produce estimates of the number of patients in the UK that should be detected. Results The rate of detection of EOAD and IPD varied very significantly and consistently between regions of the UK with low rates of detection in Northern and Western Britain (72% less detection in these regions compared with Central and Southeast Britain). The estimates from population studies further suggest a greater number of patients with EOAD than are diagnosed by genetic testing throughout the UK. Conclusions It is likely that patients with EOAD and IPD are not being recognised and referred for testing. With the prospect of meaningful disease modifying therapeutics for these diseases, this study highlights an issue of relevance to neurologists and those planning for provision of National Health Services.

Clinical Trial Simulations Based on Genetic Stratification and the Natural History of a Functional Outcome Measure in Creutzfeldt-Jakob Disease.

IMPORTANCEnA major challenge for drug development in neurodegenerative diseases is that adequately powered efficacy studies with meaningful end points typically require several hundred participants and long durations. Prion diseases represent the archetype of brain diseases caused by protein misfolding, the most common subtype being sporadic Creutzfeldt-Jakob disease (sCJD), a rapidly progressive dementia. There is no well-established trial method in prion disease.nnnOBJECTIVEnTo establish a more powerful and meaningful clinical trial method in sCJD.nnnDESIGN, SETTING, AND PARTICIPANTSnA stratified medicine and simulation approach based on a prospective interval-cohort study conducted from October 2008 to June 2014. This study involved 598 participants with probable or definite sCJD followed up over 470 patient-years at a specialist national referral service in the United Kingdom with domiciliary, care home, and hospital patient visits. We fitted linear mixed models to the outcome measurements, and simulated clinical trials involving 10 to 120 patients (no dropouts) with early to moderately advanced prion disease using model parameters to compare the power of various designs.nnnMAIN OUTCOMES AND MEASURESnA total of 2681 assessments were done using a functionally orientated composite end point (Medical Research Council Scale) and associated with clinical investigations (brain magnetic resonance imaging, electroencephalography, and cerebrospinal fluid analysis) and molecular data (prion protein [PrP] gene sequencing, PrPSc type).nnnRESULTSnOf the 598 participants, 273 were men. The PrP gene sequence was significantly associated with decline relative to any other demographic or investigation factors. Patients with sCJD and polymorphic codon 129 genotypes MM, VV, and MV lost 10% of their function in 5.3 (95% CI, 4.2-6.9), 13.2 (95% CI, 10.9-16.6), and 27.8 (95% CI, 21.9-37.8) days, respectively (P <u2009.001). Simulations indicate that an adequately powered (80%; 2-sided α =u2009.05) open-label randomized trial using 50% reduction in Medical Research Council Scale decline as the primary outcome could be conducted with only 120 participants assessed every 10 days and only 90 participants assessed daily, providing considerably more power than using survival as the primary outcome. Restricting to VV or MV codon 129 genotypes increased power even further. Alternatively, single-arm intervention studies (half the total sample size) could provide similar power in comparison to the natural history cohort.nnnCONCLUSIONS AND RELEVANCEnFunctional end points in neurodegeneration need not require long and very large clinical studies to be adequately powered for efficacy. Patients with sCJD may be an efficient and cost-effective group for testing disease-modifying therapeutics. Stratified medicine and natural history cohort approaches may transform the feasibility of clinical trials in orphan diseases.

Rare structural genetic variation in human prion diseases

Prion diseases are a diverse group of neurodegenerative conditions, caused by the templated misfolding of prion protein. Aside from the strong genetic risk conferred by multiple variants of the prion protein gene (PRNP), several other variants have been suggested to confer risk in the most common type, sporadic Creutzfeldt-Jakob disease (sCJD) or in the acquired prion diseases. Large and rare copy number variants (CNVs) are known to confer risk in several related disorders including Alzheimers disease (at APP), schizophrenia, epilepsy, mental retardation, and autism. Here, we report the first genome-wide analysis for CNV-associated risk using data derived from a recent international collaborative association study in sCJD (nxa0= 1147 after quality control) and publicly available controls (nxa0= 5427). We also investigated UK patients with variant Creutzfeldt-Jakob disease (nxa0= 114) and elderly women from the Eastern Highlands of Papua New Guinea who proved highly resistant to the epidemic prion disease kuru, who were compared with healthy young Fore population controls (nxa0= 395). There were no statistically significant alterations in the burden of CNVs >100, >500, or >1000 kb, duplications, or deletions in any disease group or geographic region. After correction for multiple testing, no statistically significant associations were found. A UK blood service control sample showed a duplication CNV that overlapped PRNP, but these were not found in prion disease. Heterozygous deletions of a 3 region of the PARK2 gene were found in 3 sCJD patients and no controls (pxa0= 0.001, uncorrected). A cell-based prion infection assay did not provide supportive evidence for a role for PARK2 in prion disease susceptibility. These data are consistent with a modest impact of CNVs on risk of late-onset neurologic conditions and suggest that, unlike APP, PRNP duplication is not a causal high-risk mutation.

Comment on validation of diagnostic criteria for variant Creutzfeldt-Jakob disease

There is no doubt that the development of diagnostic criteria has contributed greatly to epidemiological research in prion diseases, and Heath and colleagues emphasize this in surveillance studies of variant Creutzfeldt-Jakob disease (vCJD). We caution, however, against a more broad application in clinical practice, particularly in governing decisions about clinical diagnosis, communication with patients/caregivers, and access to experimental therapies. The physician looking after a young patient with an unexplained rapidly progressive neuropsychiatric syndrome, dementia, or ataxia needs to make prompt clinical decisions. There are treatable alternative diagnoses, and an early firm diagnosis is essential. The pulvinar sign on magnetic resonance imaging is often not identified when patients are first imaged, and a requirement for a clinical duration of 6 months or greater makes a probable diagnosis impossible in the early stages of disease. Physicians who have cared for families affected by vCJD are aware of the complicated psychological issues generated by the perceived mismanagement of the bovine spongiform encephalopathy epidemic, which are often exacerbated by a delay or equivocation about diagnosis. Several families also choose experimental intracerebroventricular pentosan polysulfate therapy, which requires neurosurgery. In the context of these issues, the role of tonsillar biopsy is underemphasized by Heath et al and the criteria. In our experience of 60 biopsies, by far the largest series worldwide, tonsillar biopsy has 100% sensitivity and specificity, at any stage of the disease. Prion protein deposition in the tonsil can be patchy, and at least 20 germinal centers need to be examined. The number examined in 1 French case reported by Heath et al may not have been adequate to avoid a false-negative result. It is notable that of the 6 most recent patients suspected clinically of having vCJD in the United Kingdom, 3 did not meet epidemiological criteria for probable vCJD while alive. Two of these patients would have been misdiagnosed as sporadic CJD according to the updated clinical diagnostic criteria for sporadic Creutzfeldt-Jakob Disease criteria; typical vCJD was diagnosed at autopsy in both. In a third patient, with a heterozygous codon 129 genotype reported by Kaski et al, the pulvinar sign was not thought to be present by all neuroradiologists, and no tissue was examined. It is reasonable to expect that tonsillar biopsy may have made the correct diagnosis in each of these cases. Given experience with transfusion-associated secondary vCJD, vCJD prions are likely to be present in significant titer in human blood, a diagnostic blood test based on detection of the infectious agent is clearly possible in principle, and if technologically achieved, will necessitate a complete revision of how we approach diagnosis in this disease.