Longitudinal Gompertzian analysis of amyotrophic lateral sclerosis mortality in the U.S., 1977-1986: evidence for an inherently susceptible population subset.

Age-adjusted mortality rates for amyotrophic lateral sclerosis (ALS) for men and women in the United States from 1977 to 1986 were determined and subjected to longitudinal Gompertzian analysis. The exponential decline in the rate of increase of age-adjusted ALS mortality rates after age 55 years is most consistent with the existence of an inherently susceptible population subset that is decreasing faster than the general population. In the U.S. between 1977 and 1986, annual age-adjusted ALS mortality rate distributions were determined by a common fixed intersect point (for men, the death rate at age 46.38 years was 0.91/100,000; for women, the death rate at age 45.85 years was 0.46/100,000); and an environmental factor that varied erratically during the decade by a factor of 7.21 for men and 11.64 for women. On the average, the U.S. environment during this period was 4.33 times more conducive to mortality from ALS in men than in women. Overall ALS mortality between 1977 and 1986 increased 46% and 49% for men and women, respectively. The common fixed intersect point in mortality rate distributions suggests that these increases were real and not merely the result of improved diagnosis and/or better reporting. The overall increase in ALS mortality most likely results from an effective increase in the susceptible population subset due to increasing life expectancy, rather than to environmental factors. That is, as life expectancy increases, more of the susceptible population subset live long enough to express the disease.