Epidemiological surveillance of amyotrophic lateral sclerosis and parkinsonism-dementia in the Commonwealth of the Northern Mariana Islands.

Amyotrophic lateral sclerosis (ALS) and parkinsonism-dementia (PD), two fatal neurological diseases of unknown cause, occur in high incidence among the Chamorro people of Guam, the largest and southernmost island within the Mariana archipelago. To reassess and extend our present epidemiological knowledge of these degenerative diseases in this focal geographical region, a systematic search for both disorders was conducted on the remaining inhabited islands of Rota, Tinian, Saipan, and the four remote islands of Anatahan, Alamagan, Pagan, and Agrihan within the Marianas chain. One case of ALS (on Saipan), 2 cases of PD (on Rota and Saipan), and 6 cases of parkinsonism without dementia (2 on Rota, 3 on Saipan, 1 on Tinian) were encountered among the approximately 17,000 inhabitants. No cases of either ALS, PD, or parkinsonism were found in the four remote Northern Islands. An additional 22 cases of ALS and 8 cases of PD were identified from reports of previous case-finding surveys, hospital records, and death certificates. Among Chamorros born on Rota, the average annual age-adjusted mortality rates of ALS per 100,000 population were 37.7 for the 15-year period 1956 to 1970 and 22.5 for the past decade, 1971 to 1980. Among Chamorros born on Saipan, the average annual mortality rates were 7.2 and 3.2 per 100,000, respectively, for the two periods. The mortality rates of PD were also significantly lower on Saipan than on Rota. In general, the age-adjusted mortality rates of ALS and PD on Rota were similar to those currently observed on Guam. Since the origins and current genotypic composition of Chamorros on all the Mariana Islands are indistinguishable, the strikingly lower mortality rates of ALS and PD on Saipan suggest that environmental factors are far more important than genetic factors in the pathogenesis of these diseases.