FRAGILE-X-AND-AUTISM_37289

FRAGILE-X-AND-AUTISM_37289 - C H I L D H O O D D E V E LO P...

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PERSPECTIVE NATURE NEUROSCIENCE VOLUME 9 | NUMBER 10 | OCTOBER 2006 1221 CHILDHOOD DEVELOPMENTAL DISORDERS Fragile X syndrome and autism at the intersection of genetic and neural networks Autism, an entirely behavioral diagnosis with no largely understood etiologies and no population-wide biomarkers, contrasts with fragile X syndrome (FXS), a single-gene disorder with definite alterations of gene expression and neuronal morphology. Nevertheless, the behavioral overlap between autism and FXS suggests some overlapping mechanisms. Understanding how the single-gene alteration in FXS plays out within complex genetic and neural network processes may suggest targets for autism research and illustrate strategies for relating autism to more singular genetic syndromes. The diagnosis of autism depends on a ‘triad’ of deficits comprising impaired social interaction, impaired communication and restricted interests and repetitive behaviors. Although in some cases speech never develops fully or never develops at all, in other cases speech may be pres- ent but so inflexible and unresponsive to context that it is unusable in normally paced conversation. Speech is often limited to echolalia (par- roting of rote phrases or memorized scripts, or repetition of words just spoken by others), or confined to narrow topics of expertise where dis- course can proceed without conversational interplay. The communicative impairment extends also to nonverbal signals such as gaze, facial expres- sion and gesture. Social behaviors, too, are beset by a lack of flexibility and rapid coordination: children with autism do not coordinate atten- tion between objects of mutual interest and the other people who may be interested in them, often engage in ‘parallel play’ at the edge of a group rather than joining in cooperative play, and do not in general engage in pretend play. Intense and narrowly focused interests tend to concentrate on systems that operate deterministically and repeatably according to tractable sets of rules, and behavior often is marked by motor stereotypes and compulsive actions. In addition to these diagnos- tic components, sensory hypersensitivity and motor incoordination are common features. Autism is the extreme of a spectrum of abnormalities whose milder variants include Asperger syndrome, where language is intact but social and communicative inflexibility and restricted and repetitive interests and behaviors remain, and the ‘broader autism phenotype’ in which characteristic cognitive traits are present subclini- cally. The combination of this broad variation of phenotypes and a high rate of concordance in monozygotic twins suggests a large number of genetic and environmental biasing factors 1 . FXS, in contrast, is caused by the silencing of a single gene (
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This note was uploaded on 01/23/2011 for the course BCHS 4361 taught by Professor Echberg during the Spring '09 term at University of Houston.

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FRAGILE-X-AND-AUTISM_37289 - C H I L D H O O D D E V E LO P...

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