The epidemiology of autism spectrum disorders

Underdiagnosis and referral bias of autism in ethnic minorities

This study examined (1) the distribution of ethnic minorities among children referred to autism institutions and (2) referral bias in pediatric assessment of autism in ethnic minorities. It showed that compared to the known community prevalence, ethnic minorities were under-represented among 712 children referred to autism institutions. In addition, pediatricians (n = 81) more often referred to autism when judging clinical vignettes of European majority cases (Dutch) than vignettes including non-European minority cases (Moroccan or Turkish). However, when asked explicitly for ratings of the probability of autism, the effect of ethnic background on autism diagnosis disappeared. We conclude that the use of structured ratings may decrease the likelihood of ethnic bias in diagnostic decisions of autism.

Autism and the environment: challenges and opportunities for research

Autism spectrum disorder is a complex developmental disorder that dramatically affects the lives of patients and their families and the broader community. The causes of autism are unknown; however, evidence increasingly suggests that a complex interplay among environmental stressors, genetic mutations, and other biological factors likely plays a significant role in the development and/or progression of autism spectrum disorder. On April 18 and 19, 2007, the Institute of Medicine's Forum on Neuroscience and Nervous System Disorders hosted a workshop to provide a venue to bring together scientists; major sponsors of autism-related research; and members of the autism patient, family, and advocacy community to discuss the most promising and urgent scientific questions and opportunities. Broad participation by the autism community enriched the meeting significantly by contributing a valuable and personal perspective that is often missing from scientific meetings. It also began a much improved public-private partnership in which all stakeholders are represented. On the basis of the presentations and the discussions that followed, an array of important scientific opportunities were identified in 5 general categories: (1) opportunities to advance clinical research; (2) opportunities to enhance epidemiologic studies; (3) opportunities to improve the understanding of autism's pathology and etiology; (4) tools and infrastructure needs; and (5) opportunities for public-private partnerships. This workshop demonstrated that full public engagement can greatly enhance activities such as this workshop and its outcomes. Furthermore, we expect that this listing of scientific challenges, needs, and opportunities will help to frame a more comprehensive research agenda.

Parental psychiatric disorders associated with autism spectrum disorders in the offspring

OBJECTIVE

Autism is a developmental disorder defined by impaired social interaction, communication, and behavior. Causes and correlates of autism are largely unknown, but elevated frequencies of psychiatric disorders and distinct personality traits have been reported among the family members of individuals with autism. Linkage of data from Swedish registries was used to investigate whether hospitalization for psychiatric conditions was higher among parents of children with autism compared with control subjects.

METHODS

Data sources included the Swedish Medical Birth Register (child's birth), the Swedish Multi-Generation Register (linking parents to children), and Swedish Hospital Discharge Register (hospitalization records). Children born between 1977 and 2003 who had a hospitalization record indicating autism before 10 years of age (n = 1227) were matched with 30,693 control subjects from the Swedish Medical Birth Register by gender, year of birth, and hospital. Parent diagnoses were based on an inpatient hospital diagnostic evaluation and included schizophrenia, other nonaffective psychoses, affective disorders, neurotic and personality disorders and other nonpsychotic disorders, alcohol and drug addiction and abuse, and autism. Odds ratios and 95% confidence intervals were estimated by using conditional logistic regression, adjusted for child's age, gender, hospital of birth, parents' age, country of birth and socioeconomic status, and diagnosis of a mental disorder in the other parent.

RESULTS

Parents of children with autism were more likely to have been hospitalized for a mental disorder than parents of control subjects. Schizophrenia was more common among case mothers and fathers compared with respective control parents. Depression and personality disorders were more common among case mothers but not fathers. CONCLUSIONS; This large population study supports the potential for familial aggregation of psychiatric conditions that may provide leads for future investigations of heritable forms of autism.

Deferred and immediate imitation in regressive and early onset autism

Deferred imitation has long held a privileged position in early cognitive development, considered an early marker of representational thought with links to language development and symbolic processes. Children with autism have difficulties with several abilities generally thought to be related to deferred imitation: immediate imitation, language, and symbolic play. However, few studies have examined deferred imitation in early autism. The present study examined both deferred, spontaneous imitation and immediate, elicited imitation on a set of carefully matched tasks in 36 young children with autism: 16 with early onset autism, 20 with regressive autism and two contrast groups, younger typically developing children (n = 20) and age matched children with significant developmental delays (n = 21). Analyses of co-variance controlling for differences in verbal mental age revealed significant main effects for task, but no main effect of group and no interaction of task by group. Deferred imitation scores were lower than immediate imitation scores for all groups. Imitation performance was related to overall intellectual functioning for all groups, and there were moderate and significant relations between imitation in the immediate elicited condition and in the spontaneous deferred condition for all groups. Finally, there were no differences between onset subgroups in imitation scores, suggesting that the two share a similar phenotype involving both types of imitation.

Diagnosis of autism spectrum disorders in the first 3 years of life

Autism spectrum disorders (ASDs) are a class of neurodevelopmental disorders defined by qualitative impairments in social functioning and communication, often accompanied by repetitive and stereotyped patterns of behavior and interests. The term 'ASD' encompasses autism, pervasive developmental disorder not otherwise specified, and Asperger's syndrome. ASDs show etiologic heterogeneity, and there is no definitive medical test or cure for these conditions. Around 1 in 150 children have an ASD, with males being affected three to four times more frequently than females. The age at diagnosis of ASD ranges from 3 to 6 years, but there is increasing evidence that diagnosis in the second year of life is possible in some children. Early diagnosis will lead to earlier behavior-based intervention, which is associated with improvements in core areas, such as social functioning and communication. Early detection of-and intervention to treat-ASD is crucial because it is likely to lead to an improved outcome.

Advances in behavioral genetics: mouse models of autism

Autism is a neurodevelopmental syndrome with markedly high heritability. The diagnostic indicators of autism are core behavioral symptoms, rather than definitive neuropathological markers. Etiology is thought to involve complex, multigenic interactions and possible environmental contributions. In this review, we focus on genetic pathways with multiple members represented in autism candidate gene lists. Many of these pathways can also be impinged upon by environmental risk factors associated with the disorder. The mouse model system provides a method to experimentally manipulate candidate genes for autism susceptibility, and to use environmental challenges to drive aberrant gene expression and cell pathology early in development. Mouse models for fragile X syndrome, Rett syndrome and other disorders associated with autistic-like behavior have elucidated neuropathology that might underlie the autism phenotype, including abnormalities in synaptic plasticity. Mouse models have also been used to investigate the effects of alterations in signaling pathways on neuronal migration, neurotransmission and brain anatomy, relevant to findings in autistic populations. Advances have included the evaluation of mouse models with behavioral assays designed to reflect disease symptoms, including impaired social interaction, communication deficits and repetitive behaviors, and the symptom onset during the neonatal period. Research focusing on the effect of gene-by-gene interactions or genetic susceptibility to detrimental environmental challenges may further understanding of the complex etiology for autism.

The neurobiology of autism

Improving clinical tests are allowing us to more precisely classify autism spectrum disorders and diagnose them at earlier ages. This raises the possibility of earlier and potentially more effective therapeutic interventions. To fully capitalize on this opportunity, however, will require better understanding of the neurobiological changes underlying this devastating group of developmental disorders. It is becoming clear that the normal trajectory of neurodevelopment is altered in autism, with aberrations in brain growth, neuronal patterning and cortical connectivity. Changes to the structure and function of synapses and dendrites have also been strongly implicated in the pathology of autism by morphological, genetic and animal modeling studies. Finally, environmental factors are likely to interact with the underlying genetic profile, and foster the clinical heterogeneity seen in autism spectrum disorders. In this review we attempt to link the molecular pathways altered in autism to the neurodevelopmental and clinical changes that characterize the disease. We focus on signaling molecules such as neurotrophin, Reelin, PTEN and hepatocyte growth factor, neurotransmitters such as serotonin and glutamate, and synaptic proteins such as neurexin, SHANK and neuroligin. We also discuss evidence implicating oxidative stress, neuroglial activation and neuroimmunity in autism.

Autism: transient in utero hypothyroxinemia related to maternal flavonoid ingestion during pregnancy and to other environmental antithyroid agents

The incidence and prevalence of autism have increased during the past two decades. Despite comprehensive genetic studies the cause of autism remains unknown. This review emphasizes the potential importance of environmental factors in its causation. Alterations of cortical neuronal migration and cerebellar Purkinje cells have been observed in autism. Neuronal migration, via reelin regulation, requires triiodothyronine (T3) produced by deiodination of thyroxine (T4) by fetal brain deiodinases. Experimental animal models have shown that transient intrauterine deficits of thyroid hormones (as brief as 3 days) result in permanent alterations of cerebral cortical architecture reminiscent of those observed in brains of patients with autism. I postulate that early maternal hypothyroxinemia resulting in low T3 in the fetal brain during the period of neuronal cell migration (weeks 8-12 of pregnancy) may produce morphological brain changes leading to autism. Insufficient dietary iodine intake and a number of environmental antithyroid and goitrogenic agents can affect maternal thyroid function during pregnancy. The most common causes could include inhibition of deiodinases D2 or D3 from maternal ingestion of dietary flavonoids or from antithyroid environmental contaminants. Some plant isoflavonoids have profound effects on thyroid hormones and on the hypothalamus-pituitary axis. Genistein and daidzein from soy (Glycine max) inhibit thyroperoxidase that catalyzes iodination and thyroid hormone biosynthesis. Other plants with hypothyroid effects include pearl millet (Pennisetum glaucum) and fonio millet (Digitaria exilis); thiocyanate is found in Brassicae plants including cabbage, cauliflower, kale, rutabaga, and kohlrabi, as well as in tropical plants such as cassava, lima beans, linseed, bamboo shoots, and sweet potatoes. Tobacco smoke is also a source of thiocyanate. Environmental contaminants interfere with thyroid function including 60% of all herbicides, in particular 2,4-dichlorophenoxyacetic acid (2,4-D), acetochlor, aminotriazole, amitrole, bromoxynil, pendamethalin, mancozeb, and thioureas. Other antithyroid agents include polychlorinated biphenyls (PCBs), perchlorates, mercury, and coal derivatives such as resorcinol, phthalates, and anthracenes. A leading ecological study in Texas has correlated higher rates of autism in school districts affected by large environmental releases of mercury from industrial sources. Mercury is a well known antithyroid substance causing inhibition of deiodinases and thyroid peroxidase. The current surge of autism could be related to transient maternal hypothyroxinemia resulting from dietary and/or environmental exposure to antithyroid agents. Additional multidisciplinary epidemiological studies will be required to confirm this environmental hypothesis of autism.