Rising mortality from motor neurone disease: an explanation.

There is considerable debate about the increasing mortality from motor neurone disease (MND). However, examination of the relationship between increased life expectancy (through decreased general mortality) and increased mortality in both England and Wales and the United States indicates a close association between the two variables. Using a statistical model, defined sub-populations susceptible to MND can be identified in both countries. The size of such a sub-population has been estimated from the 1989 mortality data to be approximately 160,000 people in England and Wales. The proportion of this sub-population dying from MND has increased over the last 30 years, rather than, as previously, dying at an earlier age from other conditions. On this basis, deaths from MND are expected to increase by a further 20% in this sub-population between 1991-2021 because of continuing changes in life expectancy. MND is a condition made increasingly visible in mortality statistics through decreased general mortality, rather than one in which the underlying population at risk has substantially changed. Aetiological extrapolations from the data indicate that susceptibility to the disease is acquired early in life, and that it is unlikely, given the relative stability of the underlying sub-population, that either changed environmental circumstances or artifactual factors can account in themselves for the rise in mortality.