Mercury exposure in children with autistic spectrum disorder: case-control study

Ockham's Razor and autism: the case for developmental neurotoxins contributing to a disease of neurodevelopment

Much professional awareness regarding environmental triggers for ASD has been narrowly focused on a single possible exposure pathway (vaccines). Meanwhile, empirical support for environmental toxins as a broad class has been quietly accumulating. Recent research has shown that persons with ASD have comparatively higher levels of various toxins and are more likely to have reduced detoxifying ability, and, that rates of ASD may be higher in areas with greater pollution. This report documents that within the state with the highest rate of ASD, the rate is higher for schools near EPA Superfund sites, t (332)=3.84, p=.0001. The reasons for the rise in diagnoses likely involve genetically predisposed individuals being exposed to various environmental triggers at higher rates than in past generations.

Diagnosticando o transtorno autista: aspectos fundamentais e considerações práticas

Tendo como base modelos de prática diagnóstica implementados em outros países, o objetivo do artigo é oferecer uma revisão geral acerca do que vem a ser o transtorno autista e dos fatores críticos que devem ser considerados durante o processo diagnóstico. São discutidos aspectos dos critérios diagnósticos e também das comorbidades, incidência, etiologia e diretrizes para a prática diagnóstica. Tais diretrizes incluem formas de exploração de sintomas de risco durante exames de rotina realizados por profissionais que trabalham com a população infantil e elementos básicos necessários para a realização de uma avaliação minuciosa e criteriosa por uma equipe interdisciplinar. Isso inclui, por exemplo, o uso de instrumentos específicos auxiliares no diagnóstico, elementos importantes para a avaliação médica e psicológica e encaminhamentos para serviços adequados de intervenção e apoio.

Stevens-Johnson syndrome in a child with chronic mercury exposure and 2,3-dimercaptopropane-1-sulfonate (DMPS) therapy

INTRODUCTION

Stevens-Johnson syndrome (SJS) is an uncommon and potentially serious mucocutaneous disease. The most important step in the management of SJS is early recognition and immediate withdrawal of the causative agent. We present a patient with SJS associated with dimercaptopropane-1-sulfonate (DMPS) therapy.

CASE REPORT

An asymptomatic 11-year old boy who had been exposed chronically to mercury vapour had a 24-hour urine mercury concentration of 37 microgram/L (reference value <10 microgram/L). Exposure to the mercury vapour was stopped and treatment with oral DMPS was begun. After two weeks of therapy, he developed a disseminated cutaneous eruption of red pruritic macules on his chest and back, which three days later had spread all over his body with the discrete maculae becoming confluent; erosions and crusts developed on his lips and he had blisters in his mouth. The diagnosis of SJS was made, the DMPS was stopped, and the SJS resolved gradually.

DISCUSSION

Chelation agents like DMPS or DMSA are increasingly used and are available over the counter in some countries. These drugs are used in patients with complaints that are attributed to mercury-containing dental amalgams and in children with autism.

CONCLUSION

The reported association suggests that SJS may be a potential complication of DMPS therapy, and this should be considered in the risk-benefit analysis of chelation. The reported association suggests that SJS may be a potential complication of DMPS therapy, and this should be considered in the risk-benefit analysis of chelation.

Nutritional and environmental approaches to preventing and treating autism and attention deficit hyperactivity disorder (ADHD): a review

OBJECTIVES

The purpose of this study was to concisely review the available literature of nutritional and environmental factors on autistic spectrum and attention deficit hyperactivity disorder (ADHD).

DESIGN AND METHODS

Review of journal articles found on the PubMed database and from information from several conference proceedings.

RESULTS

Many, but not all, studies link exposure to toxins such as mercury, lead, pesticides, and in utero smoking exposure to higher levels of autism and/or ADHD. Some studies have reported many nutritional deficiencies in autism/ADHD patients. Numerous studies have reported that supplemental nutrients such as omega-3 fatty acids, vitamins, zinc, magnesium, and phytochemicals may provide moderate benefits to autism/ADHD patients. Avoidance of food allergens, food chemicals, and chelation therapy may also provide some relief to autism/ADHD patients.

CONCLUSIONS

Autistic spectrum disorders and ADHD are complicated conditions in which nutritional and environmental factors play major roles. Larger studies are needed to determine optimum multifactorial treatment plans involving nutrition, environmental control,medication, and behavioral/education/speech/physical therapies.

Metal concentrations of common freshwater and marine fish from the Pearl River Delta, south China

Sediments and fish, including tilapia (Oreochromis mossambicus), bighead carp (Aristichthys nobilis), grass carp (Ctenopharyngodon idellus), and mandarin fish (Siniperca chuatsi) were collected from different fish ponds in the Pearl River Delta (Tanzhou, Sanjiao, Guangzhou, Shipai, Changan, and Mai Po) for the analysis of metalloids and heavy metals [arsenic (As), cadmium (Cd), chromium (Cr), mercury (Hg), and lead (Pb)]. The pollution of As in pond sediments was great; however, As in the edible parts of pond fish were within the international permissible safety levels for human consumption. Axial muscles from 10 species each of freshwater and marine fish purchased from markets in Hong Kong were also analyzed for As, Cd, Cr, Cu, Hg, Ni, Pb and Zn. Freshwater fish contained 0.24 to 2.13 mg/kg As, 0.10 to 0.17 mg/kg Cd, 0.09 to 0.36 mg/kg Cr, 0.06 to 0.35 mg/kg Cu, 0.07 to 0.34 mg/kg Hg, 0.04 to 0.36 mg/kg Ni, 0.11 to 0.52 mg/kg Pb, and 2.67 to 19.1 mg/kg Zn (wet weight). Marine fish had higher Hg and lower Pb concentrations than freshwater fish. A few fish species had average concentrations greater than the international standards for Cd and Pb established by the European Union and the China National Standard Management Department. Total Hg concentrations in 10 of 20 market fish species were generally greater than those of the World Health Organization's recommended limit of 0.2 mg/kg for at-risk groups, such as children and pregnant women. Daily intake through fish consumption of these metals were compared with the Provisional Tolerable Weekly Intake proposed by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives. There appears to be potential threat to local people from Hg contamination because of the high marine fish consumption rate (142 g/d/person).

The epidemiology of autism spectrum disorders

Autism spectrum disorders (ASDs) are complex, lifelong, neurodevelopmental conditions of largely unknown cause. They are much more common than previously believed, second in frequency only to mental retardation among the serious developmental disorders. Although a heritable component has been demonstrated in ASD etiology, putative risk genes have yet to be identified. Environmental risk factors may also play a role, perhaps via complex gene-environment interactions, but no specific exposures with significant population effects are known. A number of endogenous biomarkers associated with autism risk have been investigated, and these may help identify significant biologic pathways that, in turn, will aid in the discovery of specific genes and exposures. Future epidemiologic research should focus on expanding population-based descriptive data on ASDs, exploring candidate risk factors in large well-designed studies incorporating both genetic and environmental exposure data and addressing possible etiologic heterogeneity in studies that can stratify case groups and consider alternate endophenotypes.

Complementary and alternative medical therapies for attention-deficit/hyperactivity disorder and autism

Complementary and alternative medical (CAM) therapies are commonly used by parents for their children who have attention deficit hyperactivity disorder (ADHD) or autism spectrum disorders. The use of these therapies is well documented, yet the evidence of the safety and efficacy of these treatments in children is limited. This article describes the current evidence-based CAM therapies for ADHD and autism, focusing on nutritional interventions; natural health products, including essential fatty acids, vitamins, minerals, and other health supplements; biofeedback; and reducing environmental toxins. The CAM evidence in ADHD is addressed, as is the CAM literature in autism.

Blood levels of mercury are related to diagnosis of autism: a reanalysis of an important data set

The question of what is leading to the apparent increase in autism is of great importance. Like the link between aspirin and heart attack, even a small effect can have major health implications. If there is any link between autism and mercury, it is absolutely crucial that the first reports of the question are not falsely stating that no link occurs. We have reanalyzed the data set originally reported by Ip et al. in 2004 and have found that the original p value was in error and that a significant relation does exist between the blood levels of mercury and diagnosis of an autism spectrum disorder. Moreover, the hair sample analysis results offer some support for the idea that persons with autism may be less efficient and more variable at eliminating mercury from the blood.

Brief Report: Emerging Services for Children with Autism Spectrum Disorders in Hong Kong (1960–2004)

Early identification of autistic features in any child is important because there is potential for improvement by means of interventional, educational, or rehabilitative programs. Appropriate diagnosis of autism requires a dual-level approach--routine developmental surveillance and screening, and diagnosis and evaluation of autism. The historical emergence of a model of services for children with autism in Hong Kong arose because of increasing awareness, increasing prevalence, and pressure from parents and support groups. The university-based Autism Research Program at the University of Hong Kong serves as an example of an integrated center for research, teaching, and training in autism. The period from 1960 to 2004 is reviewed.

Mercury, lead, and zinc in baby teeth of children with autism versus controls

This study determined the level of mercury, lead, and zinc in baby teeth of children with autism spectrum disorder (n = 15, age 6.1 +/- 2.2 yr) and typically developing children (n = 11, age = 7 +/- 1.7 yr). Children with autism had significantly (2.1-fold) higher levels of mercury but similar levels of lead and similar levels of zinc. Children with autism also had significantly higher usage of oral antibiotics during their first 12 mo of life, and possibly higher usage of oral antibiotics during their first 36 mo of life. Baby teeth are a good measure of cumulative exposure to toxic metals during fetal development and early infancy, so this study suggests that children with autism had a higher body burden of mercury during fetal/infant development. Antibiotic use is known to almost completely inhibit excretion of mercury in rats due to alteration of gut flora. Thus, higher use of oral antibiotics in the children with autism may have reduced their ability to excrete mercury, and hence may partially explain the higher level in baby teeth. Higher usage of oral antibiotics in infancy may also partially explain the high incidence of chronic gastrointestinal problems in individuals with autism.

Autism and environmental influences: review and commentary

Progress has been slow in identifying pre- and post-natal environmental exposures that might trigger the features that characterize autism. During the past thirty years, research in the field of autism has been conducted in a setting in which diagnostic criteria for this condition have changed and broadened, and differences of opinion regarding diagnostic issues and diagnostic terminology continue. The documented prevalence of all forms of autism has increased steadily during this time, suggesting one or more environmental contributors. Not established, however, is whether an increasing incidence of autism is responsible for increasing prevalence. The increase in documented prevalence could result from expanding and changing case definitions and increased reporting due to increased awareness on the part of professionals who work with children and by the public. This review provides a background for the evolving story of autism and describes the research on the relation between autism and the environment, with a particular focus on some of the more recently proposed environmental triggers. Critical analysis of this body of scientific research in a historical framework helps to explain the often controversial nature of the proposed relations between autism and environmental factors, as well as to rationalize some of the pitfalls in research design and in the often questionable interpretation of data so obtained.

The safety of dental amalgam in children

The safety of mercury-containing dental amalgam has been hotly debated for well over a century. Dental exposures from mercury have been suggested as the cause of numerous diseases including multiple sclerosis, autism and many others. Known health effects of mercury exposure include CNS and renal damage. However, these effects have only been shown at occupational or higher levels of exposure, and have not been conclusively shown to be present at levels of mercury exposure consistent with that from dental amalgam fillings. The use of mercury amalgam fillings remains a state-of-the-art treatment for dental caries throughout the world. Although there have been a small number of peer-reviewed reports examining the health effects of dental mercury in children, only very recently have the only randomised, controlled clinical trials (two) of the safety of mercury amalgam been published. The purpose of this review is to discuss the scientific evidence on the safety of the use of mercury-containing dental amalgam as a treatment for dental caries.

Environmental mercury contamination in China: sources and impacts

This review article focused on the current status of mercury (Hg) contamination in different ecological compartments in China, and their possible environmental and health impacts, focusing on some major cities. Mercury emission from non-ferrous metals smelting (especially zinc smelting), coal combustion and miscellaneous activities (of which battery and fluorescent lamp production and cement production are the largest), contributed about 45%, 38% and 17%, respectively, to the total Hg emission based on the data of 1999. Mercury contamination is widespread in different ecological compartments such as atmosphere, soil and water. There is evidence showing bioaccumulation and biomagnification of Hg in aquatic food chains, with higher concentrations detected in carnivorous fish. In terms of human exposure to Hg, fish consumption is the major exposure pathway for residents living in coastal cities such as Hong Kong, but inhalation may be another major source, affecting human health in areas with severe atmospheric Hg, such as Guiyang City (Guizhou Province). The first case study indicated that after closure of the acetic acid plant 20 years at Songyuan City (Jilin Province), 16.7% of residents' hair still contained Hg concentration in excess of 1 mg/kg (the reference dosage value, RfD set by USEPA). The second case study indicated that the male residents of Hong Kong who consumed more than four or more meals of fish per week tended to contain higher Hg in their hair, which was linked to their subfertility. There is also increasing evidence showing that skin disorders and autism in Hong Kong children are related to their high Hg body loadings (hair, blood and urine), through prenatal methyl Hg exposure. There seems to be an urgent need to identify the sources of Hg, speciation and concentrations in different ecological compartments, which may lead to high body loadings in human beings. Adverse health effects of residents living in places with a higher background level of Hg, due to long-term exposure to chronic levels of Hg through oral intake should not be overlooked.

Pervasive developmental disorders in Montreal, Quebec, Canada: prevalence and links with immunizations

BACKGROUND

The prevalence of pervasive developmental disorders has increased in recent years. Links with the measles component of the measles-mumps-rubella vaccine and the cumulative exposure to thimerosal through other vaccines have been postulated.

OBJECTIVES

The purpose of this work was to estimate the pervasive developmental disorder prevalence in Montreal, Canada, in cohorts born from 1987 to 1998 and evaluate the relationship of trends in pervasive developmental disorder rates with: (1) changes in cumulative exposure to ethylmercury (thimerosal) occurring through modifications in the immunization schedule of young children and (2) trends in measles-mumps-rubella vaccination use rates and the introduction of a 2-measles-mumps-rubella dosing schedule during the study period.

METHODS

We surveyed 27749 children born from 1987 to 1998 attending 55 schools from the largest Anglophone school board. Children with pervasive developmental disorders were identified by a special needs team. The cumulative exposure by age 2 years to thimerosal was calculated for 1987-1998 birth cohorts. Ethylmercury exposure ranged from medium (100-125 microg) from 1987 to 1991 to high (200-225 microg) from 1992 to 1995 to nil from 1996 onwards when thimerosal was entirely discontinued. Measles-mumps-rubella coverage for each birth cohort was estimated through surveys of vaccination rates. The immunization schedule included a measles-mumps-rubella single dose at 12 months of age up to 1995, and a second measles-mumps-rubella dose at 18 months of age was added on after 1996.

RESULTS

We found 180 children (82.8% males) with a pervasive developmental disorder diagnosis who attended the surveyed schools, yielding a prevalence for pervasive developmental disorder of 64.9 per 10000. The prevalence for specific pervasive developmental disorder subtypes were, for autistic disorder: 21.6 of 10000; for pervasive developmental disorder not otherwise specified: 32.8 of 10000; and for Asperger syndrome: 10.1 of 10000. A statistically significant linear increase in pervasive developmental disorder prevalence was noted during the study period. The prevalence of pervasive developmental disorder in thimerosal-free birth cohorts was significantly higher than that in thimerosal-exposed cohorts (82.7 of 10000 vs 59.5 of 10000). Using logistic regression models of the prevalence data, we found no significant effect of thimerosal exposure used either as a continuous or a categorical variable. Thus, thimerosal exposure was unrelated to the increasing trend in pervasive developmental disorder prevalence. These results were robust when additional analyses were performed to address possible limitations because of the ecological nature of the data and to evaluate potential effects of misclassification on exposure or diagnosis. Measles-mumps-rubella vaccination coverage averaged 93% during the study interval with a statistically significant decreasing trend from 96.1% in the older birth cohorts (1988-89) to approximately 92.4% in younger birth cohorts (1996-1998). Thus, pervasive developmental disorder rates significantly increased when measles-mumps-rubella vaccination uptake rates significantly decreased. In addition, pervasive developmental disorder prevalence increased at the same rate before and after the introduction in 1996 of the second measles-mumps-rubella dose, suggesting no increased risk of pervasive developmental disorder associated with a 2-measles-mumps-rubella dosing schedule before age 2 years. Results held true when additional analyses were performed to test for the potential effects of misclassification on exposure or diagnostic status. Thus, no relationship was found between pervasive developmental disorder rates and 1- or 2-dose measles-mumps-rubella immunization schedule.

CONCLUSIONS

The prevalence of pervasive developmental disorder in Montreal was high, increasing in recent birth cohorts as found in most countries. Factors accounting for the increase include a broadening of diagnostic concepts and criteria, increased awareness and, therefore, better identification of children with pervasive developmental disorders in communities and epidemiologic surveys, and improved access to services. The findings ruled out an association between pervasive developmental disorder and either high levels of ethylmercury exposure comparable with those experienced in the United States in the 1990s or 1- or 2-dose measles-mumps-rubella vaccinations.

The contribution of diagnostic substitution to the growing administrative prevalence of autism in US special education

OBJECTIVE

Growing administrative prevalence of autism has stirred public controversy and concern. The extent to which increases in the administrative prevalence of autism have been associated with corresponding decreases in the use of other diagnostic categories is unknown. The main objective of this study was to examine the relationship between the rising administrative prevalence of autism in US special education and changes in the use of other classification categories.

METHODS

The main outcome measure was the administrative prevalence of autism among children ages 6 to 11 in US special education. Analysis involved estimating multilevel regression models of time-series data on the prevalence of disabilities among children in US special education from 1984 to 2003.

RESULTS

The average administrative prevalence of autism among children increased from 0.6 to 3.1 per 1000 from 1994 to 2003. By 2003, only 17 states had a special education prevalence of autism that was within the range of recent epidemiological estimates. During the same period, the prevalence of mental retardation and learning disabilities declined by 2.8 and 8.3 per 1000, respectively. Higher autism prevalence was significantly associated with corresponding declines in the prevalence of mental retardation and learning disabilities. The declining prevalence of mental retardation and learning disabilities from 1994 to 2003 represented a significant downward deflection in their preexisting trajectories of prevalence from 1984 to 1993. California was one of a handful of states that did not clearly follow this pattern.

CONCLUSIONS

Prevalence findings from special education data do not support the claim of an autism epidemic because the administrative prevalence figures for most states are well below epidemiological estimates. The growing administrative prevalence of autism from 1994 to 2003 was associated with corresponding declines in the usage of other diagnostic categories.

Developmental neurotoxicology

The developing brain has a distinctive set of characteristics that make it unusually sensitive to damage by toxic agents. Mechanistic understanding of the vulnerability of the immature nervous system to various chemicals is important from a preventive perspective but has also frequently given us new insights into maturation of neural circuitry. This review examines some of the developmental consequences of contact with various exogenous agents, including metals, solvents, pharmaceuticals, and natural products. This review emphasizes how subtle suboptimal brain function rather than acute toxicity can be a consequence of chemical exposures occurring during ontogenesis. The rate of brain aging may be influenced by events taking place in embryogenesis, following a prolonged asymptomatic period. The potential for appearance of adverse effects after prolonged latent periods is underscored.

Environmental mercury exposure in children: South China's experience

BACKGROUND

Environmental mercury levels significantly increased in the past decades following its increase in industrial applications. In spite of an increasing concern on the potential harmful effects of mercury on children, there is no reported data for the Chinese population. The relationship between dietary habit and environmental mercury exposure in Chinese children was studied.

METHODS

The hair and blood mercury levels of Chinese children aged above 3 years in 2000 March to September, were studied. Sociodemographic data, dietary habits of the past 6 months, and other risk factors for environmental mercury exposure were collected. Those children with blood mercury levels above the toxic range (i.e. > 45 nmol/L) and their family members were further evaluated and their blood and hair mercury levels were monitored before and after Fishing-Moratorium period (June to August 2000) in South China Sea.

RESULTS

Altogether, 137 Chinese children (mean age, 7.2 years) were recruited. The mean hair mercury level was 2.2 p.p.m and the mean blood mercury level was 17.6 nmol/L. There was a strong correlation (r = 0.88) between hair and blood mercury levels in our cohort. Frequency of fish consumption correlated with hair (r = 0.51) and blood (r = 0.54) mercury levels. For those children who consumed fish more than 3 times/week, hair and blood mercury levels were twice as high as those who consumed fish l-3 times/week and threefold of those who never consumed fish. Five children and 12 family members had toxic blood mercury levels. Their blood (P < 0.0001) and hair (P = 0.02) mercury levels dropped significantly after reducing fish consumption during Fishing-Moratorium period.

CONCLUSION

Both blood and hair (i.e. Tissue) mercury levels of children in Hong Kong was elevated and correlated with the frequency of fish consumption.