1. Aoki Y, Abe O, Nippashi Y, Yamasue H. {{Comparison of white matter integrity between autism spectrum disorder subjects and typically developing individuals: a meta-analysis of diffusion tensor imaging tractography studies}}. {Mol Autism};2013 (Jul 22);4(1):25.
BACKGROUND: Aberrant brain connectivity, especially with long-distance underconnectivity, has been recognized as a candidate pathophysiology of autism spectrum disorders. However, a number of diffusion tensor imaging studies investigating people with autism spectrum disorders have yielded inconsistent results. METHODS: To test the long-distance underconnectivity hypothesis, we performed a systematic review and meta-analysis of diffusion tensor imaging studies in subjects with autism spectrum disorder. Diffusion tensor imaging studies comparing individuals with autism spectrum disorders with typically developing individuals were searched using MEDLINE, Web of Science and EMBASE from 1980 through 1 August 2012. Standardized mean differences were calculated as an effect size of the tracts. RESULTS: A comprehensive literature search identified 25 relevant diffusion tensor imaging studies comparing autism spectrum disorders and typical development with regions-of-interest methods. Among these, 14 studies examining regions of interest with suprathreshold sample sizes were included in the meta-analysis. A random-effects model demonstrated significant fractional anisotropy reductions in the corpus callosum (P = 0.023, n = 387 (autism spectrum disorders/typically developing individuals: 208/179)), left uncinate fasciculus (P = 0.011, n = 242 (117/125)), and left superior longitudinal fasciculus (P = 0.016, n = 182 (96/86)), and significant increases of mean diffusivity in the corpus callosum (P = 0.006, n = 254 (129/125)) and superior longitudinal fasciculus bilaterally (P = 0.031 and 0.011, left and right, respectively, n = 109 (51/58)), in subjects with autism spectrum disorders compared with typically developing individuals with no significant publication bias. CONCLUSION: The current meta-analysis of diffusion tensor imaging studies in subjects with autism spectrum disorders emphasizes important roles of the superior longitudinal fasciculus, uncinate fasciculus, and corpus callosum in the pathophysiology of autism spectrum disorders and supports the long-distance underconnectivity hypothesis.
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2. Ecker C, Ronan L, Feng Y, Daly E, Murphy C, Ginestet CE, Brammer M, Fletcher PC, Bullmore ET, Suckling J, Baron-Cohen S, Williams S, Loth E, Murphy DG. {{Intrinsic gray-matter connectivity of the brain in adults with autism spectrum disorder}}. {Proc Natl Acad Sci U S A};2013 (Jul 22)
Autism spectrum disorders (ASD) are a group of neurodevelopmental conditions that are accompanied by atypical brain connectivity. So far, in vivo evidence for atypical structural brain connectivity in ASD has mainly been based on neuroimaging studies of cortical white matter. However, genetic studies suggest that abnormal connectivity in ASD may also affect neural connections within the cortical gray matter. Such intrinsic gray-matter connections are inherently more difficult to describe in vivo but may be inferred from a variety of surface-based geometric features that can be measured using magnetic resonance imaging. Here, we present a neuroimaging study that examines the intrinsic cortico-cortical connectivity of the brain in ASD using measures of « cortical separation distances » to assess the global and local intrinsic « wiring costs » of the cortex (i.e., estimated length of horizontal connections required to wire the cortex within the cortical sheet). In a sample of 68 adults with ASD and matched controls, we observed significantly reduced intrinsic wiring costs of cortex in ASD, both globally and locally. Differences in global and local wiring cost were predominantly observed in fronto-temporal regions and also significantly predicted the severity of social and repetitive symptoms (respectively). Our study confirms that atypical cortico-cortical « connectivity » in ASD is not restricted to the development of white-matter connections but may also affect the intrinsic gray-matter architecture (and connectivity) within the cortical sheet. Thus, the atypical connectivity of the brain in ASD is complex, affecting both gray and white matter, and forms part of the core neural substrates underlying autistic symptoms.
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3. Huguet G, Ey E, Bourgeron T. {{The Genetic Landscapes of Autism Spectrum Disorders}}. {Annu Rev Genomics Hum Genet};2013 (Jul 22)
The autism spectrum disorders (ASD) are characterized by impairments in social interaction and stereotyped behaviors. For the majority of individuals with ASD, the causes of the disorder remain unknown; however, in up to 25% of cases, a genetic cause can be identified. Chromosomal rearrangements as well as rare and de novo copy-number variants are present in approximately 10-20% of individuals with ASD, compared with 1-2% in the general population and/or unaffected siblings. Rare and de novo coding-sequence mutations affecting neuronal genes have been also identified in approximately 5-10% of individuals with ASD. Common variants such as single-nucleotide polymorphisms seem to contribute to ASD susceptibility, but their effects appear to be small. Despite a heterogeneous genetic landscape, the genes implicated thus far-which are involved in chromatin remodeling, metabolism, mRNA translation, and synaptic function-seem to converge in common pathways affecting neuronal and synaptic homeostasis. Animal models developed to study these genes should lead to a better understanding of the diversity of the genetic landscapes of ASD. Expected final online publication date for the Annual Review of Genomics and Human Genetics Volume 14 is August 31, 2013. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
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4. Moss BG, Chugani DC. {{Increased Risk of Very Low Birth Weight, Rapid Postnatal Growth, and Autism in Underweight and Obese Mothers}}. {Am J Health Promot};2013 (Jul 22)
Abstract Purpose . To determine whether prepregnancy weight was associated with children’s birth weight, early physical growth, and autism diagnosis. Design . Early Childhood Longitudinal Study-Birth Cohort data. Setting . United States. Subjects . Representative sample of U.S. children followed from birth through kindergarten (n = 4800). Also, a subpopulation of the very low birth weight children was examined (n = 500). Measures . Maternal variables included age and prepregnancy body mass index. Changes in children’s height, weight, and head circumference between 9 months and 2 years were used as growth metrics. Children’s sex, age, birth weight, and reported autism were also considered. Analysis . Logistic and multinomial logistic models assessed the impact of prepregnancy weight on birth weight and children’s subsequent rate of physical growth and autism. Results . Children born to underweight or obese mothers had increased odds of very low birth weight. Very low birth weight was related to rapid height and weight growth and more than twice the likelihood to subsequently be diagnosed with autism. For the subgroup of very low birth weight children, rapid head growth was related to a fivefold increase in the odds of autism. After accounting for the impact birth weight and growth rates, we found prepregnancy weight indirectly impacted autism risk. Conclusion . Being underweight or obese during prepregnancy indirectly increased risk for autism from increased odds of low birth weight and accelerated postnatal growth.
