Abstract
Autism spectrum disorder (ASD) is a heterogeneous condition affecting an individual’s ability to communicate and socialize and often presents with repetitive movements or behaviors. It tends to be severe with less than 10% achieving independent living with a marked variation in the progression of the condition. To date, the literature supports a multifactorial model with the largest, most detailed twin study demonstrating strong environmental contribution to the development of the condition. Here, we present a brief review of the neurological, immunological, and autonomic abnormalities in ASD focusing on the causative roles of environmental agents and abnormal gut microbiota. We present a working hypothesis attempting to bring together the influence of environment on the abnormal neurological, immunological, and neuroimmunological functions and we explain in brief how such pathophysiology can lead to, and/or exacerbate ASD symptomatology. At present, there is a lack of consistent findings relating to the neurobiology of autism. Whilst we postulate such variable findings may reflect the marked heterogeneity in clinical presentation and as such the variable findings may be of pathophysiological relevance, more research into the neurobiology of autism is necessary before establishing a working hypothesis. Both the literature review and hypothesis presented here explore possible neurobiological explanations with an emphasis of environmental etiologies and are presented with this bias.
Highlights
Autism spectrum disorder (ASD) is a neurodevelopmental disorder of unknown etiology
Supporting these findings, cancer mortality rates are higher in ASD [20], and the only identified risk factor for mortality associated with the recent H1N1 outbreak was developmental delay [30]
The theory of clostridia involvement was postulated by Bolte in 1998 who suggested that clostridia toxin adversely affected neurotransmitter function that could result in neurobehavioral changes presenting as autism [68]
Summary
Autism spectrum disorder (ASD) is a neurodevelopmental disorder of unknown etiology. Recent evidence suggests a strong environmental component [1] and persistent neuroinflammation [2,3,4,5]. Research efforts have focused more on the genetic aspects of ASD than on environmental factors over the previous 15 years [8]. A recent twin study published in July 2011 was well-designed with a substantial statistical power. The study concluded: autism has substantial environmental factors, and the environmental factors were of more significance than genetic factors [1]. Since its discovery in the late 1930s, autism has gradually become the diagnosis of choice It has replaced and superseded childhood schizophrenia and feeblemindedness and has encompassed within the spectrum, a host of neurodevelopmental disorders [for review see Ref. We briefly discuss the pertinent literature concerning the frequently reported abnormal www.frontiersin.org
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