Ehp Niehs Nih Members 2005 7743

Ehp Niehs Nih Members 2005 7743

Neuro Development
An article in the May 2005 issue of EHP putsthe economic cost to the United States of methylmercury-inducedtoxicity (in terms of lost productivity) at $8.7 billionannually.the effects of low-dose exposures are not so apparent.Two large epidemiologic studies of fishing populationsin the Faroe Islands and the Seychelles have produced conflictingresults regarding low-dose effects. Both studies soughtto examine the association between methylmercury exposureand NeuroDevelopment in children whose mothers ate contaminatedseafood during pregnancy.the leader of the Faroe Islands study, Philippe Grandjean,an adjunct professor of environmental health at the HarvardSchool of Public Health, and his colleagues reported inthe November 1997 issue of Neurotoxicology and Teratology that7-year-old Faroese children had significant cognitive deficitsand neurological changes after prenatal exposure to methylmercury.Grandjean’s team followed up on the children at age14. According to a report in the February 2004 issue of TheJournal of Pediatrics, the children continued to haveproblems, including neurological changes and decreasednervous control of the heart.In contrast, the authors of the Seychelles study foundlittle evidence of lasting harm on a cohortof 66-month-old children, according to their report inthe 26 August 1998issue of JAMA. A follow-up study, published in the17 May 2003 issue of the Lancet, similarlyfound no lasting effects on language, memory,motor skills, or behavioral function when the childrenwere 9 years old.the different outcomes of the two studies are puzzlingbecause the children of both populations appeared to beexposed to similar amounts of methylmercury. Several explanationshave been proposed, including the possibility that geneticdifferences between the populations may alter their relativepredispositions to harm from mercury exposure. the sourceof methylmercury is also different in the two populations.the Faroese are exposed primarily through the consumptionof pilot whale meat, whereas the Seychelles populationrelies heavily on ocean fish. According to Gary Myers,a professor of neurology and pediatrics at the Universityof Rochester Medical Center and one of the principal investigatorsof the Seychelles study, whale meat contains many othercontaminants (including PCBs) besides methylmercury. Thereis also evidence, he says, that the effectsof concomitant PCB and mercury exposure are synergistic.Researchers continue to look at whether there is a dangerfrom methylmercury at the levels of exposure achieved byfish consumption. Another layer of uncertainty was addedwith findings published in the October 2005 issue of EHP showingthat fish consumption during pregnancy appeared to boostinfant cognition-- But only as long as mercury intake, asmeasured in maternal hair, wasn’t too high.the question of whether low levels of mercury are harmfulhas also manifested itself in a controversy over the useof vaccines containing thimerosal, a preservative. Althoughthimerosal was removed from many of these vaccines in 2001,children that were immunized before that date could havereceived a cumulative dose of more than 200 ug/kgof mercury with the routine complement of childhood vaccinations,according to a study in the May 2001 issue of Pediatrics.Thimerosal is nearly half ethylmercury by weight. Becauseethylmercury is an organic form of mercury, there is somesuspicion that it acts like methylmercury in the brain,although research published in the August 2005 issue of EHP suggeststhat the two forms differ greatly in how they are distributedthrough and eliminated from the brain. Developing countriescontinue to use pediatric vaccines that contain thimerosal.In the United States, thimerosal is still present in influenzavaccines, which the CDC recommends be given to pregnantwomen and children aged 6-23 months.Advocacy groups, such as SafeMinds, have suggested thatthe decades- Long rise in the diagnosis of autism is relatedto the presence of thimerosal in vaccines. In May 2004,however, the Institute of Medicine (IOM) issued a report, ImmunizationSafety Review: Vaccines and Autism, stating that severalepidemiological studies published since 2001 consistentlyprovided evidence of no association between thimerosal- Containingvaccines and autism. However, the IOM’s report hasbeen severely criticized by a number of advocacy groups,including the National Autism Association, for relyingtoo heavily on a specific set of epidemiologic data whiledismissing clinical evidence and other epidemiologic studiesthat showed evidence of a link.Despite the assurances of the IOM, some scientists continueto explore the mechanisms underlying the potential neurotoxiceffects of thimerosal. In the January 2005 issue of NeuroToxicology,S. Jill James, a professor of pediatrics at the Universityof Arkansas for Medical Sciences, and her colleagues reportthat the neuronal and glial cell toxicity of methylmercuryand ethylmercury (as dosed via thimerosal) are both mediatedby the depletion of the antioxidant peptide glutathione.of the two cell types, neurons were found to be particularlysusceptible to ethylmercury-induced glutathione depletionand cell death, according to James, and pretreatment ofthe cells with glutathione reduced these effects. Otherstudies by James and her colleagues, reported in the December2004 issue of the American Journal of Clinical Nutrition,showed that autistic children had lower levels of glutathionecompared to normal controls, and may therefore have hada significant reduction in the ability to detoxify reactiveoxygen species.James says the abnormal profile suggests thatthese children may have an increased vulnerability to pro-oxidantenvironmental exposures and a lower threshold for oxidativeneurotoxicity and immunotoxicity. Speaking at theXXII International Neurotoxicology Conference in September2005, she presented evidence that multiple genetic polymorphismsaffecting glutathione pathways may interact to producea chronic metabolic imbalance that could contribute tothe development and clinical symptoms of autism. Her paperin the American Journal of Clinical Nutrition reportedthat low glutathione levels in many autistic children werereversible with targeted nutritional intervention, but

Ehp Niehs Nih Members 2005 7743

Web Site
Ehp Niehs Nih Members 2005 7743 7743 - Toxins - Find in Neurodevelopment and Health
Ehp Niehs Nih Members 2005 7743 7743 - Toxins in Neurodevelopment and Health

Ehp Niehs Nih Members 2005 7743 Neurodevelopment
Ehp Niehs Nih Members 2005 7743 2018