ALZHEIMERS-DISEASE - PRELIMINARY-STUDY OF SPATIAL-DISTRIBUTION AT BIRTH PLACE

Alzheimer's disease (AD) is a neurodegenerative disorder which is char acterized by a progressive loss of memory and the alteration of cognit ive functions. At least three chromosomal segments have been associate d with early-onset AD in genetic linkage studies. These results argue for a certain degree of heterogeneity in the genetic origin of some fo rms of AD, although environmental risk factors cannot be ruled out in late-onset AD. In this preliminary study, we analyzed the geographical distribution of the birth places of a sample of 235 AD cases born in a defined region of Quebec (Canada), between 1895 and 1935. We wished to test the hypothesis that risk factors acting at, or around birth pl ace and time play a role in the etiology of AD. The field of study was divided into rural and urban areas. A reference population of live bi rths was used to compute a measure of odds ratio (OR). The OR results showed a statistically significant excess of AD cases in the rural are a as compared to the reference population. When stratified for sex, th e OR results showed a global excess of female AD cases in both the rur al and the urban areas. For men, only the urban area presented a stati stically significant deficit. We also analyzed the structures of the g enealogical kinships of the rural and urban sub-groups. Although AD ca ses from the rural sub-group were more closely related to each other t han those from the urban one, removal of the kin pairs from the OR ana lysis seemed to have little effect on the rural/urban distribution of cases. Therefore, the OR results would not appear to be due primarily to a difference in the kinship structures of the two sub-groups. This could mean that some risk factors for AD afflict women more strongly t han men, the effect being different depending on the urban or rural or igin. However, potential biases such as a higher rare of report for wo men, differential migration between birth places or a differential mor tality ratio between sexes could produce spurious results in the direc tion of what we have observed in this preliminary study.