Childhood Disintegrative Disorder: Distinction From Autistic Disorder and Predictors of Outcome
ABSTRACT Childhood disintegrative disorder, a rare, relentlessly progressive neurologic disorder, first described by Heller in 1908, remains a condition of great interest. It has long been debated whether it is a discrete disorder or simply a late-onset variant of childhood autism. We have studied 6 cases of childhood disintegrative disorder, collected over 8 years, and followed for 2.5 to 22 years (mean 8.6 years). Childhood disintegrative disorder begins later in life than autism, and following a period of entirely normal development; the regression is more global and more severe than in autism; seizures are more frequent than in autism, yet demonstrable organicity in childhood disintegrative disorder is decidedly rare. Lastly, the prognosis is usually much worse than in autism, but in those cases with neither seizures nor epileptiform activity on electroencephalography (EEG), the outcome may be more favorable. Childhood disintegrative disorder should be viewed as a condition distinct from childhood autism.
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- "Two assumptions of the hypothesis need supporting evidence and further computational models: the assumption that long-range connectivity (necessary to explain the behavioural phenotype in ASD) is any more vulnerable to pruning than short-range connectivity; and the assumption that there are individual differences in the onset and rate of pruning that explain variations in ASD trajectories but do not manifest in marked differences in typical development. Further work is required, for instance, to consider possible variations in timing of developmental regression, and whether the proposed sources of variation could account for the late-occurring regression observed in childhood disintegrative disorder (Rosman & Bergia, 2013). The over-pruning hypothesis stems from a high-level artificial neural network model, but further clarification is needed in translating to a more general hypothesis that can be tested through neuroscientific or behavioural data. "
ABSTRACT: This article outlines the over-pruning hypothesis of autism. The hypothesis originates in a neurocomputational model of the regressive sub-type (Thomas, Knowland & Karmiloff-Smith, 2011a, 2011b). Here we develop a more general version of the over-pruning hypothesis to address heterogeneity in the timing of manifestation of ASD, including new computer simulations which reconcile the different observed developmental trajectories (early onset, late onset, regression) via a single underlying atypical mechanism; and which show how unaffected siblings of individuals with ASD may differ from controls either by inheriting a milder version of the pathological mechanism or by co-inheriting the risk factors without the pathological mechanism. The proposed atypical mechanism involves overly aggressive synaptic pruning in infancy and early childhood, an exaggeration of a normal phase of brain development. We show how the hypothesis generates novel predictions that differ from existing theories of ASD including that (1) the first few months of development in ASD will be indistinguishable from typical, and (2) the earliest atypicalities in ASD will be sensory and motor rather than social. Both predictions gain cautious support from emerging longitudinal studies of infants at-risk of ASD. We review evidence consistent with the over-pruning hypothesis, its relation to other current theories (including C. Frith's under-pruning proposal; C. Frith, 2003, 2004), as well as inconsistent data and current limitations. The hypothesis situates causal accounts of ASD within a framework of protective and risk factors (Newschaffer et al., 2012); clarifies different versions of the broader autism phenotype (i.e. the implication of observed similarities between individuals with autism and their family members); and integrates data from multiple disciplines, including behavioural studies, neuroscience studies, genetics, and intervention studies. © 2015 John Wiley & Sons Ltd.Developmental Science 04/2015; DOI:10.1111/desc.12303 · 3.89 Impact Factor
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ABSTRACT: In humans, brain connectivity implements a system for language and communication that spans from basic pre-linguistic social abilities shared with non-human primates to syntactic and pragmatic functions particular to our species. The arcuate fasciculus is a central connection in this architecture, linking regions devoted to formal aspects of language with regions involved in intentional and social communication. Here, we outline a new anatomical model of communication that incorporates previous neurofunctional accounts of language with recent advances in tractography and neuropragmatics. The model consists of five levels, from the representation of informative actions and communicative intentions, to lexical/semantic processing, syntactic analysis, and pragmatic integration. The structure of the model is hierarchical in relation to developmental and evolutionary trajectories and it may help interpreting clinico-anatomical correlation in communication disorders.Current Opinion in Neurobiology 08/2014; 28C:165-171. DOI:10.1016/j.conb.2014.07.018 · 6.77 Impact Factor
- 12/2014; DOI:10.5350/DAJPN2014270411