Dafydd Thomas

Investigation of variant Creutzfeldt-Jakob disease and other human prion diseases with tonsil biopsy samples

BACKGROUND Prion diseases are associated with the accumulation of an abnormal isoform of cellular prion protein (PrPSc), which is the principal constituent of prions. Prions replicate in lymphoreticular tissues before neuroinvasion, suggesting that lymphoreticular biopsy samples may allow early diagnosis by detection of PrPSc. Variant Creutzfeldt-Jakob disease (variant CJD) is difficult to distinguish from common psychiatric disorders in its early stages and definitive diagnosis has relied on neuropathology. We studied lymphoreticular tissues from a necropsy series and assessed tonsillar biopsy samples as a diagnostic investigation for human prion disease. METHODS Lymphoreticular tissues (68 tonsils, 64 spleens, and 40 lymph nodes) were obtained at necropsy from patients affected by prion disease and from neurological and normal controls. Tonsil biopsy sampling was done on 20 patients with suspected prion disease. Tissues were analysed by western blot to detect and type PrPSc, by PrP immunohistochemistry, or both. FINDINGS All lymphoreticular tissues obtained at necropsy from patients with neuropathologically confirmed variant CJD, but not from patients with other prion diseases or controls, were positive for PrPSc. In addition, PrPSc typing revealed a consistent pattern (designated type 4t) different from that seen in variant CJD brain (type 4) or in brain from other CJD subtypes (types 1-3). Tonsil biopsy tissue was positive in all eight patients with an adequate biopsy sample and whose subsequent course has confirmed, or is highly consistent with, a diagnosis of variant CJD and negative in all patients subsequently confirmed to have other diagnoses. INTERPRETATION We found that if, in the appropriate clinical context, a tonsil biopsy sample was positive for PrPSc, variant CJD could be diagnosed, which obviates the need for a brain biopsy sample to be taken. Our results also show that variant CJD has a different pathogenesis to sporadic CJD.

Kuru in the 21st century—an acquired human prion disease with very long incubation periods

BACKGROUND Kuru provides the principal experience of epidemic human prion disease. Its incidence has steadily fallen after the abrupt cessation of its route of transmission (endocannibalism) in Papua New Guinea in the 1950s. The onset of variant Creutzfeldt-Jakob disease (vCJD), and the unknown prevalence of infection after the extensive dietary exposure to bovine spongiform encephalopathy (BSE) prions in the UK, has led to renewed interest in kuru. We investigated possible incubation periods, pathogenesis, and genetic susceptibility factors in kuru patients in Papua New Guinea. METHODS We strengthened active kuru surveillance in 1996 with an expanded field team to investigate all suspected patients. Detailed histories of residence and exposure to mortuary feasts were obtained together with serial neurological examination, if possible. FINDINGS We identified 11 patients with kuru from July, 1996, to June, 2004, all living in the South Fore. All patients were born before the cessation of cannibalism in the late 1950s. The minimum estimated incubation periods ranged from 34 to 41 years. However, likely incubation periods in men ranged from 39 to 56 years and could have been up to 7 years longer. PRNP analysis showed that most patients with kuru were heterozygous at polymorphic codon 129, a genotype associated with extended incubation periods and resistance to prion disease. INTERPRETATION Incubation periods of infection with human prions can exceed 50 years. In human infection with BSE prions, species-barrier effects, which are characteristic of cross-species transmission, would be expected to further increase the mean and range of incubation periods, compared with recycling of prions within species. These data should inform attempts to model variant CJD epidemiology.

Safety and efficacy of quinacrine in human prion disease (PRION-1 study): a patient-preference trial

Summary Background The propagation of prions, the causative agents of Creutzfeldt-Jakob disease and other human prion diseases, requires post-translational conversion of normal cellular prion protein to disease-associated forms. The antimalarial drug quinacrine (mepacrine) prevents this conversion in vitro, and was given to patients with various prion diseases to assess its safety and efficacy in changing the course of these invariably fatal and untreatable diseases. Methods Patients with prion disease were recruited via the UK national referral system and were offered a choice between quinacrine (300 mg daily), no quinacrine, or randomisation to immediate quinacrine or deferred quinacrine in an open-label, patient-preference trial. The primary endpoints were death and serious adverse events possibly or probably related to the study drug. This study is registered, ISRCTN 06722585. Findings 107 patients with prion disease (45 sporadic, two iatrogenic, 18 variant, and 42 inherited) were enrolled, 23 in a pilot study and 84 in the main study. Only two patients chose randomisation; 40 took quinacrine during follow-up (37 who chose it at enrolment). Choice of treatment was associated with disease severity, with those least and most severely affected more likely to choose not to receive quinacrine. 78 (73%) patients died: one randomly assigned to deferred treatment, 26 of 38 who chose immediate quinacrine, and 51 of 68 who chose no quinacrine. Although adjusted mortality was lower in those who chose to take quinacrine than in those who did not, this was due to confounding with disease severity, and there was no difference in mortality between groups after adjustment. Four of 40 patients who took quinacrine had a transient response on neurological rating scales. Only two of 14 reported serious adverse events were judged quinacrine-related. Interpretation Quinacrine at a dose of 300 mg per day was reasonably tolerated but did not significantly affect the clinical course of prion diseases in this observational study. Funding Department of Health (England); UK Medical Research Council.

Prospective study of HTLV-I infection in an initially asymptomatic cohort

A prospective clinical study of 20 initially asymptomatic HTLV-I-seropositive carriers was commenced in 1991 to determine the natural history of the infection in relation to HTLV-I proviral load, immune responses, and lymphocyte phenotype. Proviral load varied widely between carriers but was relatively constant within an individual over time. The lymphocyte phenotype and prevalence of activated lymphocytes were not predictive of disease and the magnitude of the cytotoxic T-lymphocyte response to HTLV-I was independent of proviral load. Incident conditions, some related to HTLV-I infection, including a case of HTLV-I-associated myelopathy (HAM), were documented in 9 carriers. Development of myelopathy and uveitis was associated with high peripheral blood HTLV-I proviral load that predated symptoms. Persistently high proviral load appears to predate the development of HTLV-I-associated inflammation in neuro-ophthalmic tissue.

A clinical study of kuru patients with long incubation periods at the end of the epidemic in Papua New Guinea

Kuru is so far the principal human epidemic prion disease. While its incidence has steadily declined since the cessation of its route of transmission, endocannibalism, in Papua New Guinea in the 1950s, the arrival of variant Creutzfeldt–Jakob disease (vCJD), also thought to be transmitted by dietary prion exposure, has given kuru a new global relevance. We investigated all suspected cases of kuru from July 1996 to June 2004 and identified 11 kuru patients. There were four females and seven males, with an age range of 46–63 years at the onset of disease, in marked contrast to the age and sex distribution when kuru was first investigated 50 years ago. We obtained detailed histories of residence and exposure to mortuary feasts and performed serial neurological examination and genetic studies where possible. All patients were born a significant period before the mortuary practice of transumption ceased and their estimated incubation periods in some cases exceeded 50 years. The principal clinical features of kuru in the studied patients showed the same progressive cerebellar syndrome that had been previously described. Two patients showed marked cognitive impairment well before preterminal stages, in contrast to earlier clinical descriptions. In these patients, the mean clinical duration of 17 months was longer than the overall average in kuru but similar to that previously reported for the same age group, and this may relate to the effects of both patient age and PRNP codon 129 genotype. Importantly, no evidence for lymphoreticular colonization with prions, seen uniformly in vCJD, was observed in a patient with kuru at tonsil biopsy.

Video Rating in Neurodegenerative Disease Clinical Trials: The Experience of PRION-1

Background/Aims: Large clinical trials including patients with uncommon diseases involve assessors in different geographical locations, resulting in considerable inter-rater variability in assessment scores. As video recordings of examinations, which can be individually rated, may eliminate such variability, we measured the agreement between a single video rater and multiple examining physicians in the context of PRION-1, a clinical trial of the antimalarial drug quinacrine in human prion diseases. Methods: We analysed a 43-component neurocognitive assessment battery, on 101 patients with Creutzfeldt-Jakob disease, focusing on the correlation and agreement between examining physicians and a single video rater. Results: In total, 335 videos of examinations of 101 patients who were video-recorded over the 4-year trial period were assessed. For neurocognitive examination, inter-observer concordance was generally excellent. Highly visual neurological examination domains (e.g. finger-nose-finger assessment of ataxia) had good inter-rater correlation, whereas those dependent on non-visual clues (e.g. power or reflexes) correlated poorly. Some non-visual neurological domains were surprisingly concordant, such as limb muscle tone. Conclusion: Cognitive assessments and selected neurological domains can be practically and accurately recorded in a clinical trial using video rating. Video recording of examinations is a valuable addition to any trial provided appropriate selection of assessment instruments is used and rigorous training of assessors is undertaken.