Pathogenesis of autism: a patchwork of genetic causes

The expanding genomic landscape of autism: discovering the 'forest' beyond the 'trees'

Autism spectrum disorders are neurodevelopmental disorders characterized by significant deficits in reciprocal social interactions, impaired communication and restricted, repetitive behaviors. As autism spectrum disorders are among the most heritable of neuropsychiatric disorders, much of autism research has focused on the search for genetic variants in protein-coding genes (i.e., the 'trees'). However, no single gene can account for more than 1% of the cases of autism spectrum disorders. Yet, genome-wide association studies have often identified statistically significant associations of genetic variations in regions of DNA that do not code for proteins (i.e., intergenic regions). There is increasing evidence that such noncoding regions are actively transcribed and may participate in the regulation of genes, including genes on different chromosomes. This article summarizes evidence that suggests that the research spotlight needs to be expanded to encompass far-reaching gene-regulatory mechanisms that include a variety of epigenetic modifications, as well as noncoding RNA (i.e., the 'forest'). Given that noncoding RNA represents over 90% of the transcripts in most cells, we may be observing just the 'tip of the iceberg' or the 'edge of the forest' in the genomic landscape of autism.

Animal model of autism induced by prenatal exposure to valproate: altered glutamate metabolism in the hippocampus

Autism spectrum disorders (ASD) are characterized by deficits in social interaction, language and communication impairments and repetitive and stereotyped behaviors, with involvement of several areas of the central nervous system (CNS), including hippocampus. Although neurons have been the target of most studies reported in the literature, recently, considerable attention has been centered upon the functionality and plasticity of glial cells, particularly astrocytes. These cells participate in normal brain development and also in neuropathological processes. The present work investigated hippocampi from 15 (P15) and 120 (P120) days old male rats prenatally exposed to valproic acid (VPA) as an animal model of autism. Herein, we analyzed astrocytic parameters such as glutamate transporters and glutamate uptake, glutamine synthetase (GS) activity and glutathione (GSH) content. In the VPA group glutamate uptake was unchanged at P15 and increased 160% at P120; the protein expression of GLAST did not change neither in P15 nor in P120, while GLT1 decreased 40% at P15 and increased 92% at P120; GS activity increased 43% at P15 and decreased 28% at P120; GSH content was unaltered at P15 and had a 27% increase at P120. These data highlight that the astrocytic clearance and destination of glutamate in the synaptic cleft might be altered in autism, pointing out important aspects to be considered from both pathophysiologic and pharmacological approaches in ASD.

GABAergic activity in autism spectrum disorders: an investigation of cortical inhibition via transcranial magnetic stimulation

Mounting evidence suggests a possible role for γ-aminobutyric acid (GABA) in the neuropathophysiology of autism spectrum disorders (ASD), but the extent of this impairment is unclear. A non-invasive, in vivo measure of GABA involves transcranial magnetic stimulation (TMS) of the primary motor cortex to probe cortical inhibition. Individuals diagnosed with ASD (high-functioning autism or Asperger's disorder) (n = 36 [28 male]; mean age: 26.00 years) and a group of healthy individuals (n = 34 [23 male]; mean age: 26.21 years) (matched for age, gender, and cognitive function) were administered motor cortical TMS paradigms putatively measuring activity at GABAA and GABAB receptors (i.e., short and long interval paired pulse TMS, cortical silent period). All cortical inhibition paradigms yielded no difference between ASD and control groups. There was, however, evidence for short interval cortical inhibition (SICI) deficits among those ASD participants who had experienced early language delay, suggesting that GABA may be implicated in an ASD subtype. The current findings do not support a broad role for GABA in the neuropathophysiology of ASD, but provide further indication that GABAA could be involved in ASD where there is a delay in language acquisition. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Virtual conversation partner for adults with autism

Autistic Spectrum Disorder (ASD) is notable for severely impaired reciprocal social interaction skills relative to language and intellectual abilities, presenting a major barrier to social integration and vocational success. Evidence-based interventions to address these needs are lacking. We report on the development of a small, prototype conversation simulation to teach conversational skills to adolescents and adults with ASD and average to superior intellectual abilities. We also report on a test of the feasibility and acceptability of the simulation approach with a sample of the target population. The simulation engages the user in a virtual conversation with an on-screen partner whose reactions provide naturalistic feedback geared to the appropriateness of the learner's response choices. The prototype simulation, which provides for up to 12 potentially unique multi-turn conversations, was used over a period of 2 weeks by 16 adolescents and adults who then rated statements about the system on a linear scale of 1 (disagreement) to 5 (high agreement). The participants highly endorsed the majority of positive statements about the quality and credibility of the interaction and the virtual conversation partner. In contrast, agreement with positive statements about instructional features external to the conversation was moderate. Unexpectedly, most participants strongly agreed that using the simulation had been helpful to them. Further development and testing in the context of a controlled study with randomized assignment to control and experimental groups are needed to determine whether this approach is effective in improving real-world pragmatic language behavior of high-functioning adults with ASD.