Epidemiological and clinical patterns of western pacific amyotrophic lateral sclerosis (ALS) in Guam and sporadic ALS in Rochester, Minnesota, U.S.A. and Hokkaido, Japan: a comparative study.

Western Pacific amyotrophic lateral sclerosis (ALS) in Guam, so-called Guam ALS, is a neurodegenerative disease with a high incidence among the indigenous population, Chamorros, in Guam. To clarify the differences in the epidemiological and clinical features between Guam ALS and sporadic ALS, the surveys were conducted in Guam for the periods from 1980 to 1989, in Rochester, MN, USA from 1952 to 1991 and in Hokkaido, Japan from 1980 to 1989. The crude incidence rate of Guam ALS was 7.5/100,000/year, which was much higher than the rates of sporadic ALS, 2.3/100,000/year in Rochester and 0.6/100,000/year in Hokkaido, although it was markedly low as compared with that in the most frequent period between 1950-1960s. There was no remarkable change in the incidence rate either in Rochester or Hokkaido island during the above study periods. The average age of onset of Guam ALS was 56, which was more than 10 years advancement occurring in the past 40 years, although it was still younger than 68 and 58 in the sporadic ALS cases in Rochester and Hokkaido island, respectively. The average duration of the illness in Guam ALS was 36 months, which was almost the same as those in Rochester (31 months) and Hokkaido (31 months). The changing ecology and socioeconomic conditions in the past 40 years in Guam might have contributed to the drastic reduction in the environmental risk factors. However, the incidence remains high during the past decade, which suggests their genetic predisposition to Guam ALS.