Background. Globally, Parkinsonism, multiple sclerosis and. amyotrophic lateral sclerosis mortalities tends to increase with latitude. These disorders also display a north-south. gradient in the coterminous United States. This spatial distribution suggests their etiologies are significantly influenced by one or more geographical variables.

Methods. Pearson's correlation was used to compare mortalities, at the state scale, in the United States, from. these three nearologic disorders and the spatial patterns of 81 other diseases and 219 environmental variables.

Results. The resulting correlations suggest that mortality from Parkinsonism, multiple sclerosis and amyotrophic lateral sclerosis occurs most often in recently glaciated, iodine deficient regions, that were formerly marked by elevated goiter prevalence.

Conclusions, Long-term iodine deficiency appears linked to abnormalities in the dopaminergic system that include an increased number oj'dopamine receptors. It is argued that this raises susceptibility to dopamine oxidation which, in tarn, causes deficiencies of the antioxidant enzymes Cu/Zn superoxide dismutase, glutathione peroxidase and catalase. Dopamine deficiency also leads to elevated cytotoxic glutamate levels. Implications of the iodine-dipachrom.e-glut.a.mate hypothesis, for treatment of these three neurologic disorders, are then discussed. Possible interventions include the use of levodopa, vitamin Bs, Coemyme Qio, various antioxidants, amino acids, iodine and glutamate antagonists.

Key words: Parkinson's disease, multiple sclerosis, amyotrophic lateral sclerosis, glaciation, iodine, goiter, dopamine, dopachrome, glutamate, oxidative stress.