Alzheimer's disease, Parkinson's disease, and motoneurone disease: abiotrophic interaction between ageing and environment?

The hypothesis is that Alzheimer's disease, Parkinson's disease (PD), and motoneurone disease are due to environmental damage to specific regions of the central nervous system and that the damage remains subclinical for several decades but makes those affected especially prone to the consequences of age-related neuronal attrition. This proposal is based on the association between environmental factors and certain neurodegenerative diseases (eg, methylphenyltetra-hydropyridine and parkinsonism, poliovirus infection and post-poliomyelitis syndrome, chickling pea ingestion and lathyrism, an unidentified environmental factor and amyotrophic lateral sclerosis-PD complex of Guam, and trauma and pugilist's encephalopathy) and on the long latent period between exposure to environmental factor and the appearance of symptoms in some of these disorders. The practical implications of this hypothesis are that epidemiological attention should be focussed on the environment in early rather than late life, prevention may be a realistic goal if the cause of subclinical damage can be identified, a search should be undertaken for causal mechanisms linking subclinical neuronal damage due to an environmental factor and the normal ageing process, and (4) better understanding of the regional selective vulnerability of the nervous system to the ageing process might allow a rational approach to treatment.