International Journal of Toxicology
Amy S. Holmes (Baton Rouge, Louisiana, USA), Mark F. Blaxill (Safe Minds, Cambridge, Massachusetts, USA), Boyd E. Haley (Chemistry Department, University of Kentucky, Lexington, Kentucky, USA)
The autism rates reported have increased significantly in the United States and the United Kingdom. A possible factor behind these increases is the increase in mercury exposure through thimerosal-containing vaccines, but vaccine exposures need to be assessed in the context of cumulative exposures during gestation and early childhood. Differential rates of postnatal mercury elimination may explain why such gestational and infantile exposures produce variable neurological effects. The first children's haircut samples were obtained from 94 children diagnosed with autism using the diagnostic and statistical criteria of mental disorders, 4th edition (DSM IV) and 45 age and gender checks. Information on diet, dental amalgam fillings, vaccine history, administration of Rho D immunoglobulins and severity of autism symptoms were collected through a maternal investigation questionnaire and clinical observation. Hair mercury levels in the autistic group were 0,47 ppm versus 3,63 ppm in controls, a significant difference. Mothers in the autistic group had significantly higher levels of mercury exposure through Rho D immunoglobulin injections and amalgam fillings than control mothers. Within the autistic group, hair mercury levels varied significantly among moderately, moderately and severely autistic children, with average group levels of 0,79, 0,46 and 0,21 ppm, respectively. Hair mercury levels between controls were significantly related to the number of mothers' amalgam fillings and their consumption of fish, as well as to mercury exposure through childhood vaccines, correlations that were absent in the autistic group. Hair excretion patterns among autistic infants were significantly reduced compared to control. These data question the effectiveness of traditional hair analysis as a measure of total mercury exposure in a subset of the population. In light of the biological plausibility of the role of mercury in neurodevelopmental disorders, the present study provides further information on a possible mechanism by which early mercury exposures could increase the risk of autism.