Autism or autisms? The clinical manifestations and classification of autism spectrum disorders
Urbach, Jonathan Aaron
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Individuals with Autism Spectrum Disorders (autistic disorder, Asperger's disorder, childhood disintegrative disorder, and pervasive developmental disorder - not otherwise specified) are a very heterogeneous group. The disorders on the spectrum are behaviorally defined (according to the American Psychiatric Association's Diagnostic and Statistical Manual-IV, Text Revision) with specific behaviors falling within categories. For autistic disorder, the categories reflect the core deficits of social interaction, communication, and restricted or repetitive behaviors or interests ("CDC- Autism Spectrum Disorder (ASDs)- NCBDDD," n.d.). The behaviors that fall within these categories have been carefully researched and described in order to allow for uniformity in diagnosis and the discussion of causality in research. The diagnosis of Autism Spectrum Disorders (ASD) relies on established thresholds within these categories, with the clinician responsible for characterizing and counting the number of behaviors that are present and in which category they fall. Other associated symptoms (low IQ, language impairments, epilepsy, and others) are often present, and while not diagnostic of ASD, can contribute much to the phenotypic heterogeneity. As a result, individuals who exhibit different behavioral symptoms might be diagnostically indistinguishable. This thesis is intended to be a critical review of the current state of autism research. In the different sections (Phenotype, Epidemiology, Genetics, Cellular/Molecular Mechanisms, Neural Circuits, and Therapeutics), the discussion is focused on what has been firmly established in the field. In many cases, what is known about autism leads to a better understanding of how to subdivide the population. Genetics, for instance, can divide autism into syndromic or idiopathic cases (those associated with a comorbid genetic condition such as Rett's Syndrome or Fragile X and those that have no apparent genetic etiology, respectively). Epidemiology research has shown that a host of chemical, social, and emotional exposures are correlated with varied risks of developing autism (leading to possible distinctions between autism caused by teratogens or autism caused by other mechanisms). Molecular research has revealed a subset of autistic individuals who have various causes of synaptic dysfunction, and within this group there have been certain proteins implicated, offering additional points of differentiation between individuals. The study of therapeutics, however, has largely left the population as a whole in research. As a result, the comparisons (based on mean differences between controls and ASD subjects) are not fine-grained enough to show benefits within certain subgroups of ASD individuals. What the research shows is that the autism spectrum can (and should) be subdivided. Establishing multiple well-defined "autisms" allows for much more targeted research. The first step is creating clear boundaries to the spectrum, and the proposed revisions to the Fifth Edition of the Diagnostic and Statistical Manual is intended to do just this (collapsing the spectrum disorders into one diagnosis with a streamlined set of common behavioral features). The answer to the "autism or autisms?" questions is both: once the spectrum is clearly distinguished from the non-spectrum, research will establish the points at which autism should be subdivided. Homogeneous subgroups (however they are defined) will allow for more robust study of the underlying pathophysiology and possible treatment options.
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