• For 1944 through 1985, documented clinical descriptions compatible with a diagnosis of parkinsonism-dementia complex were found in 363 Chamorros (including mixed Chamorros) and three Filipino immigrants who had lived on Guam before onset. Downward trends in age-adjusted incidence rates and upward trends in age at onset were seen for Chamorros of both sexes. Since 1980, new cases have occurred only among persons over 50 years of age, whereas a younger age at onset had been noted in the past. Evidence suggests that the length of the latent period varied widely (up to decades) and increased with time, the risk of acquiring parkinsonism-dementia complex had declined since the late 1950s, and the critical age of exposure to an unknown factor in the environment on Guam appears to have been during adolescence or adulthood.
Zhang Z, Anderson DW, Lavine L, Mantel N. Patterns of Acquiring Parkinsonism-Dementia Complex on Guam1944 Through 1985. Arch Neurol. 1990;47(9):1019–1024. doi:10.1001/archneur.1990.00530090097019