Academic journal article Environmental Health Perspectives

Blood Mercury Concentrations in CHARGE Study Children with and without Autism

Academic journal article Environmental Health Perspectives

Blood Mercury Concentrations in CHARGE Study Children with and without Autism

Article excerpt

BACKGROUND: Some authors have reported higher blood mercury (Hg) levels in persons with autism, relative to unaffected controls.

OBJECTIVES: We compared blood total Hg concentrations in children with autism or autism spectrum disorder (AU/ASD) and typically developing (TD) controls in population-based samples, and determined the role of fish consumption in differences observed.

METHODS: The Childhood Autism Risk from Genetics and the Environment (CHARGE) Study enrolled children 2-5 years of age. After diagnostic evaluation, we analyzed three groups: AU/ASD, non-AU/ASD with developmental delay (DD), and population-based TD controls. Mothers were interviewed about household, medical, and dietary exposures. Blood Hg was measured by inductively coupled plasma mass spectrometry. Multiple linear regression analysis was conducted (n = 452) to predict blood Hg from diagnostic status controlling for Hg sources.

RESULTS: Fish consumption strongly predicted total Hg concentration. AU/ASD children ate less fish. After adjustment for fish and other Hg sources, blood Hg levels in AU/ASD children were similar to those of TD children (p = 0.75); this was also true among non-fish eaters (p = 0.73). The direct effect of AU/ASD diagnosis on blood Hg not through the indirect pathway of altered fish consumption was a 12% reduction. DD children had lower blood Hg concentrations in all analyses. Dental amalgams in children with gum-chewing or teeth-grinding habits predicted higher levels.

CONCLUSIONS: After accounting for dietary and other differences in Hg exposures, total Hg in blood was neither elevated nor reduced in CHARGE Study preschoolers with AU/ASD compared with unaffected controls, and resembled those of nationally representative samples.

KEY WORDS: autism, autism spectrum disorders, child development, dental amalgams, developmental delay, fish, mercury, metabolism, metals. Environ Health Perspect 118:161-166 (2010). doi:10.1289/ehp.0900736 available via http://dx.doi.org/ [Online 19 October 2009]

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Autism is a pervasive developmental disorder characterized by deficits in reciprocal social interactions and communication and by stereotyped, repetitive behaviors or a restricted range of interests. Autism spectrum disorders (ASDs) also include Asperger's syndrome, a milder form of autism, and "pervasive developmental delay-not otherwise specified" [Diagnostic and Statistical Manual of Mental Disorders, 4th ed. (American Psychiatric Association 2000)]. Established risk factors include male sex (Fombonne 2003), higher maternal and/or paternal age (Durkin et al. 2008), and family history of ASD (Piven et al. 1991). Heritability is high (Ritvo et al. 1985), and genomewide association studies indicate linkage with regions on every chromosome, suggesting a large number of genes may confer heightened autism susceptibility (Spence et al. 1985; Ylisaukko-oja et al. 2006). Two decades ago, Folstein and Rutter (1988) concluded: "Quite often it is not autism itself that is inherited but rather some genetic abnormality of language or sociability that interacts with other factors to produce autism." With discordance in up to 40% of monozygotic twin pairs, differential gene expression in autism cases compared with unaffected individuals (Gregg et al. 2008; Kelleher and Bear 2008), and epigenetic variation in DNA methylation (LaSalle 2007), environmental influences plausibly act both in concert with and independently of heritable factors.

Because of its known neurotoxicity, mercury has drawn particular attention in relation to autism. Investigations have compared measurements of Hg in blood, hair, or urine in children with versus without autism. Measurements on specimens collected before a diagnosis could, at least theoretically, shed light on the causal hypothesis. One group reported lower concentrations in the first haircut from children with autism (Holmes et al. …

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