The transmissible spongiform encephalopathies: pathogenic mechanisms and strategies for therapeutic intervention

Clinical features and diagnosis of human prion diseases

Human prion diseases are a group of progressive, fatal encephalopathies united by their similar neuropathological features, their potential transmissibility and a core molecular feature: a conformational change in prion protein. They exist in sporadic/idiopathic, genetic and acquired forms. The clinical features vary according to a number of factors, including cause and the prion protein genotype of the affected individual. Common features include dementia, cerebellar ataxia and involuntary movements. There is no absolute clinical diagnostic test; definitive diagnosis is neuropathological. However, MRI, electroencephalogram, cerebrospinal fluid protein tests, genetic tests and tonsil biopsy, can be very helpful in supporting a clinical diagnosis. The development of a noninvasive diagnostic test (e.g., on blood) would be very helpful in terms of easier, earlier clinical diagnosis, as well as having other applications (such as blood donor screening or population infection prevalence surveys). A relatively new technique (protein misfolding cyclic amplification) holds promise as such a test. Various therapeutic approaches have been suggested, but there is no current effective treatment and there are significant problems in the assessment of any candidate therapies.

Intraventricular pentosan polysulphate in human prion diseases: an observational study in the UK

BACKGROUND, PURPOSE AND METHODS: This observational study assessed the effect of continuous intraventricular infusion of pentosan polysulphate (PPS) in seven patients at different clinical centres in the UK.

RESULTS

Complications of intraventricular catheterization were frequent. PPS was well-tolerated over a wide dose range (11-110 microg/kg/day) during the 6-month study. Four patients were assessed for the entire study period: one remained stable, two showed minimal deterioration and one progressed significantly.

CONCLUSION

Mean survival of all patients was longer than reported values for natural history of specific prion disorders. Possible reasons for these findings are explored.

What is the basis of transmissible spongiform encephalopathy induced neurodegeneration and can it be repaired?

Once an animal becomes infected with a prion disease, or transmissible spongiform encephalopathy (TSE), the progression of infection is relentless and inevitably fatal, although often with such prolonged incubation periods that an alternative cause of death can intervene. Infection has been compared to 'setting a clock' which then runs inexorably as the disease spreads, usually through the lymphoreticular system and then via peripheral nerves to the central nervous system (CNS), although the mechanism controlling the protracted progression is not known. Clinical disease develops as characteristic degenerative changes in the CNS progress, but the molecular basis for this pathology is not clear, particularly the relationship between the deposition of abnormal PrP and neuronal dysfunction. Recent research has identified several means of slowing (if not stopping) the clock when infection has not yet reached the CNS; although the potential for later stage therapies seems limited, neuroprotective strategies which have been shown to be effective in other neurodegenerative conditions may also ameliorate TSE induced CNS pathology. This review focuses on our current knowledge of the key events following infection of the CNS and the opportunities for intervention once the CNS has become infected.