MOTOR-NEURON-DISEASE ON GUAM - TEMPORAL OCCURRENCE, 1941-85

Using a case registry, we investigated the temporal occurrence of moto r neuron disease (MND) on Guam. MND with onset during 1941-85 was docu mented in 434 Chamorros and 9 non-Chamorro migrants who had lived on G uam before onset. Increased median age at onset and decreased age-adju sted incidence rates (since the early 1960s) were observed for Chamorr os of both sexes. Our evidence about MND on Guam is consistent with: 1 ) The latent period duration has varied from years to decades; 2) With time, the exposure period or latent period, or both, have lengthened; 3) The high risk of acquiring the condition has been reduced since, a t least, the early 1950s, and the most recent years of meaningful risk were the early to middle 1960s; 4) The critical age for acquiring the condition is in adolescence and adulthood; 5) Change of environment f rom Guam to overseas during childhood resulted in decreased risk of ac quiring the condition.