Wednesday, May 16, 2007

Autism Spectrum Disorder & mercury study from University of Missouri-Columbia

The increase in the number of diagnosed casesof autism in recent years has sparked concern that environmentaltoxins may cause this complex disorder. However, a new University ofMissouri-Columbia study concludes that exposure to Rh immune globulinpreserved with mercury-containing thimerosal before birth was nohigher for children with autism."This study adds to the evidence that there is no casual associationbetween thimerosal and childhood autism," said Judith Miles, who isthe William S. Thomson Endowed Chair of Autism and professor ofpediatrics and pathology in the MU School of Medicine. "We concludethat there is no indication that pregnancies resulting in childrenwith autism were more likely to be complicated by Rh immuneglobulin/thimerosal exposure."The study investigated thimerosal exposure during pregnancies thatresulted in the birth of a child subsequently diagnosed with autism.Although experts anticipate that autism will be the firstbehavioral/psychiatric disorder for which major genes will beidentified, there is still fierce debate that thimerosal, apreservative commonly used in vaccines and is almost 50 percentethylmercury, is responsible for the rise in the disorder. Rhnegative women are routinely treated with Rh immune globulin (RhIg)during the third trimester to prevent hemolytic disease, in which themother's immune system attacks fetal blood cells. Like many vaccines,RhIg manufactured in the United States contained thimerosal prior to2001. Since young fetal brains are more susceptible to neurotoxiceffects, researchers led by Miles, of the MU Thompson Center forAutism and Neurodevelopmental Disorders, assessed Rh status andthimerosal exposure of mothers of children with autism.The study included 214 mothers of 230 children diagnosed with anautism spectrum disorder. Rh status, RhIg with thimerosal exposureand Rh incompatibility (in which the mother's Rh status is differentthan the fetus's) were established by reviewing medical records. Theresults showed that in children with autism, Rh negative status wasno higher in their mothers than in the general population, thatexposure to RhIg (preserved with thimerosal) before birth was nohigher and that pregnancies were not more likely to be Rhincompatible."We hope this report of no association between autism, Rh negativityand thimerosal exposure during pregnancy will offset some of thedecreased compliance with immunization recommendations which is knownto increase morbidity and mortality from childhood infectiousdiseases," Miles said. Autism diagnoses have increased significantly during the past twodecades, which coincides temporally with the addition of fivepediatric vaccines to the immunization schedule, exposing children toincreasing doses of ethylmercury, a known toxin. Though the vastmajority of studies indicate no association between vaccines andautism, the FDA, CDC and American Academy of Pediatrics recommendedthat thimerosal be removed from all routinely recommended earlychildhood vaccines; this was accomplished by 2002. Miles points out that even though RhIg and childhood vaccines are nowfree of thimerosal in the United States, it is important to analyzequestions of safety since thimerosal continues to be used in manyplaces around the world to preserve vaccines to help make themaffordable. Miles said that few studies have focused on pregnancies of Rhnegative mothers who received RhIg during pregnancy, probably becausethe thimerosal is diluted before reaching the fetus and has beenassumed to be innocuous. Nevertheless, there is a concern that evenvery small doses delivered when the brain is especially sensitive canbe toxic. Numerous Internet sites and one research study assert thatRhIg causes autism and that a high percentage of mothers of childrenwith autism are Rh negative, neither of which was shown to be true inthe current study. In addition, a recent study hypothesized that Rhincompatibility itself could disrupt fetal neurodevelopment, thusplaying a role in autism, but the current study found no increase inthe proportion of Rh incompatibility in mothers of autistic children.In response to the claim that only certain groups of children are atrisk, the authors also analyzed specific autism spectrum disordersubgroups and found that none had significant increases in either Rhnegativity or thimerosal exposure during pregnancy.The study -- "Lack of Association Between Rh Status, Rh ImmuneGlobulin in Pregnancy and Autism" -- was published in the May 2007issue of the American Journal of Medical Genetics.Note: This story has been adapted from a news release issued byUniversity of Missouri-Columbia.