| Using state of birth as a surrogate variable for early childhood environment, a proportional mortality study was conducted to determine if state of birth is a risk factor associated with motor neuron disease (MND) and Parkinson's disease (PD). A gradient of risk by geographic area in the United States was found for MND and PD when mapping the predicted probabilities of death by state of birth.;United States death certificate information for 1981 was studied. Cerebral vascular accident (CVA) deaths served as a comparison group. Multiple sclerosis (MS) deaths were analyzed to validate the methods used. Prior studies have associated early childhood exposures with MS and have found a north-south gradient in prevalence and incidence rates.;Data mapping, using proportional mortality ratios by state of birth, revealed distinct geographic patterns. A geographic relationship between longitude and proportional mortality ratios for MND, PD and MS by state of birth, and a geographic relationship between latitude and proportional mortality ratios for MND and MS by state of birth was found.;A modified case-control design was used to evaluate risk factors associated with MND, PD, MS and CVA mortality when compared to all other deaths in the United States by state of birth or state of residence at death. Statistical modeling explored whether the visual centers of each state in latitude and longitude, age, sex and migration (those who were born and died in the same state compared to those who were born and died in different states) fit the data for each of these diseases. The resulting models were evaluated by state of birth to determine if any individual states were not well represented by the model for each disease. The predicted probabilities for each of the diseases were then summed by state of birth and mapped. As predicted, no pattern was evident for CVA. The geographic gradient seen for MS is as predicted by other studies. The geographic pattern found for MND has a northwest to southeast gradient and the pattern found for PD has a west to east gradient in predicted probabilities. |
