Time to give up on a single explanation of autism

Francesca Happé, Angelica Ronald and Robert Plomin are at the Institute of Psychiatry, Kings College London, De Crispigny Park, London SE5 8AF, UK.
Nature Neuroscience (Impact Factor: 16.1). 11/2006; 9(10):1218-20. DOI: 10.1038/nn1770
Source: PubMed


We argue that there will be no single (genetic or cognitive) cause for the diverse symptoms defining autism. We present recent evidence of behavioral fractionation of social impairment, communication difficulties and rigid and repetitive behaviors. Twin data suggest largely nonoverlapping genes acting on each of these traits. At the cognitive level, too, attempts at a single explanation for the symptoms of autism have failed. Implications for research and treatment are discussed.

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    • "Besides the common dogma that genetic components are the basis for ASD, there is not a single responsible gene(s) that has been definitively linked to ASD as the causative factor (Berg and Geschwind, 2012;Griswold et al., 2015;Happé et al., 2006;Tammimies et al., 2015). As a matter of fact more than 1000 genes or SNPs have been linked to ASD (Berg and Geschwind, 2012;Griswold et al., 2015;Happé et al., 2006;Tammimies et al., 2015). However, there are several epigenetic factors that have been identified to be possible co-factors in ASD etiology (Dumas and Sikela, 2009;Fraga et al., 2005;Kim and State, 2014;Tammimies et al., 2015). "
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    ABSTRACT: Autism spectrum disorders (ASD) are highly heterogeneous developmental conditions characterized by deficits in social interaction, verbal and nonverbal communication, and obsessive/stereotyped patterns of behavior and repetitive movements. Social interaction impairments are the most characteristic deficits in ASD. There is also evidence of impoverished language and empathy, a profound inability to use standard nonverbal behaviors (eye contact, affective expression) to regulate social interactions with others, difficulties in showing empathy, failure to share enjoyment, interests and achievements with others, and a lack of social and emotional reciprocity. In developed countries, it is now reported that 1%–1.5% of children have ASD, and in the US 2015 CDC reports that approximately one in 45 children suffer from ASD. Despite the intense research focus on ASD in the last decade, the underlying etiology remains unknown. Genetic research involving twins and family studies strongly supports a significant contribution of environmental factors in addition to genetic factors in ASD etiology. A comprehensive literature search has implicated several environmental factors associated with the development of ASD. These include pesticides, phthalates, polychlorinated biphenyls, solvents, air pollutants, fragrances, glyphosate and heavy metals, especially aluminum used in vaccines as adjuvant. Importantly, the majority of these toxicants are some of the most common ingredients in cosmetics and herbicides to which almost all of us are regularly exposed to in the form of fragrances, face makeup, cologne, air fresheners, food flavors, detergents, insecticides and herbicides. In this review we describe various scientific data to show the role of environmental factors in ASD.
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    • "It should be recognised, of course, that differences in ToM are not all there is to ASD. The defining symptoms of rigid and repetitive activity and interests are not well explained by ToM deficits, and elsewhere I have suggested that ASD may be better conceptualized as a compound of different and 'fractionable' cognitive characteristics (Happé et al. 2006; Brunsdon & Happé, 2014), including differences (rather than deficits) in cognitive style that predispose to talent in areas where detail-focus is advantageous (Happé & Vital 2009). These other aspects of ASD, and recent theories proposing a single explanation for social and nonsocial features (e.g. "

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    • "Although ASD is a heterogeneous diagnosis with diverse etiologies (Happé et al., 2006; Tuchman et al., 2009), early failures in neuronal genesis, maturation, and migration have been proposed as a root pathological mechanism (Casanova and Casanova, 2014; Ecker and Murphy, 2014). This hypothesis is supported by high rates of developmental malformations in people with ASD on post-mortem neuropathological evaluations (Casanova et al., 2013; Stoner et al., 2014; Wegiel et al., 2010, 2012). "
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    ABSTRACT: Malformations of cortical development are found at higher rates in autism spectrum disorder (ASD) than in healthy controls on postmortem neuropathological evaluation but are more variably observed on visual review of in-vivo MRI brain scans. This may be due to the visually elusive nature of many malformations on MRI. Here, we utilize a quantitative approach to determine whether a volumetric measure of heterotopic gray matter in the white matter is elevated in people with ASD, relative to typically developing controls (TDC). Data from a primary sample of 48 children/young adults with ASD and 48 age-, and gender-matched TDCs, selected from the Autism Brain Imaging Data Exchange (ABIDE) open-access database, were analyzed to compare groups on (1) blinded review of high-resolution T1-weighted research sequences; and (2) quantitative measurement of white matter hypointensity (WMH) volume calculated from the same T1-weighted scans. Groupwise WMH volume comparisons were repeated in an independent, multi-site sample (80 ASD/80 TDC), also selected from ABIDE. Visual review resulted in equivalent proportions of imaging abnormalities in the ASD and TDC group. However, quantitative analysis revealed elevated periventricular and deep subcortical WMH volumes in ASD. This finding was replicated in the independent, multi-site sample. Periventricular WMH volume was not associated with age but was associated with greater restricted repetitive behaviors on both parent-reported and clinician-rated assessment inventories. Thus, findings demonstrate that periventricular WMH volume is elevated in ASD and associated with a higher degree of repetitive behaviors and restricted interests. Although the etiology of focal WMH clusters is unknown, the absence of age effects suggests that they may reflect a static anomaly.
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