Autism is a severe neurobehavioral syndrome, arising largely as an inherited disorder, which can arise from several diseases. Despite recent advances in identifying some genes that can cause autism, its underlying neurological mechanisms are uncertain. Autism is best conceptualized by considering the neural systems that may be defective in autistic individuals. Recent advances in understanding neural systems that process sensory information, various types of memories and social and emotional behaviors are reviewed and compared with known abnormalities in autism. Then, specific genetic abnormalities that are linked with autism are examined. Synthesis of this information leads to a model that postulates that some forms of autism are caused by an increased ratio of excitation/inhibition in sensory, mnemonic, social and emotional systems. The model further postulates that the increased ratio of excitation/inhibition can be caused by combinatorial effects of genetic and environmental variables that impinge upon a given neural system. Furthermore, the model suggests potential therapeutic interventions.

https://onlinelibrary.wiley.com/doi/epdf/10.1034/j.1601-183X.2003.00037.x

Model of autism: increased ratio of excitation/inhibition in key neural systems

Autism is a neurodevelopmental disorder characterized by impaired communication and social interaction and may be accompanied by mental retardation and epilepsy. Its cause remains unknown, despite evidence that genetic, environmental, and immunological factors may play a role in its pathogenesis. To investigate whether immune-mediated mechanisms are involved in the pathogenesis of autism, we used immunocytochemistry, cytokine protein arrays, and enzyme-linked immunosorbent assays to study brain tissues and cerebrospinal fluid (CSF) from autistic patients and determined the magnitude of neuroglial and inflammatory reactions and their cytokine expression profiles. Brain tissues from cerebellum, midfrontal, and cingulate gyrus obtained at autopsy from 11 patients with autism were used for morphological studies. Fresh-frozen tissues available from seven patients and CSF from six living autistic patients were used for cytokine protein profiling. We demonstrate an active neuroinflammatory process in the cerebral cortex, white matter, and notably in cerebellum of autistic patients. Immunocytochemical studies showed marked activation of microglia and astroglia, and cytokine profiling indicated that macrophage chemoattractant protein (MCP)-1 and tumor growth factor-beta1, derived from neuroglia, were the most prevalent cytokines in brain tissues. CSF showed a unique proinflammatory profile of cytokines, including a marked increase in MCP-1. Our findings indicate that innate neuroimmune reactions play a pathogenic role in an undefined proportion of autistic patients, suggesting that future therapies might involve modifying neuroglial responses in the brain.

/pdf/neuroglial-activation-and-neuroinflammation-in-the-brain-of-34g5qush00.pdf

Neuroglial activation and neuroinflammation in the brain of patients with autism

Many studies have supported a genetic etiology for autism. Here we report mutations in two X-linked genes encoding neuroligins NLGN3 and NLGN4 in siblings with autism-spectrum disorders. These mutations affect cell-adhesion molecules localized at the synapse and suggest that a defect of synaptogenesis may predispose to autism.

https://www.hal.inserm.fr/inserm-00124744/document

Mutations of the X-linked genes encoding neuroligins NLGN3 and NLGN4 are associated with autism.

SHANK3 (also known as ProSAP2) regulates the structural organization of dendritic spines and is a binding partner of neuroligins; genes encoding neuroligins are mutated in autism and Asperger syndrome. Here, we report that a mutation of a single copy of SHANK3 on chromosome 22q13 can result in language and/or social communication disorders. These mutations concern only a small number of individuals, but they shed light on one gene dosage-sensitive synaptic pathway that is involved in autism spectrum disorders.

https://www.hal.inserm.fr/inserm-00126175/document

Mutations in the gene encoding the synaptic scaffolding protein SHANK3 are associated with autism spectrum disorders.

Deficits in social interaction are important early markers for autism and related neurodevelopmental disorders with strong genetic components. Standardized behavioral assays that measure the preference of mice for initiating social interactions with novel conspecifics would be of great value for mutant mouse models of autism. We developed a new procedure to assess sociability and the preference for social novelty in mice. To quantitate sociability, each mouse was scored on measures of exploration in a central habituated area, a side chamber containing an unfamiliar conspecific (stranger 1) in a wire cage, or an empty side chamber. In a secondary test, preference for social novelty was quantitated by presenting the test mouse with a choice between the first, now-familiar, conspecific (stranger 1) in one side chamber, and a second unfamiliar mouse (stranger 2) in the other side chamber. Parameters scored included time spent in each chamber and number of entries into the chambers. Five inbred strains of mice were tested, C57BL/6J, DBA/2J, FVB/NJ, A/J and B6129PF2/J hybrids. Four strains showed significant levels of sociability (spend- ing more time in the chamber containing stranger 1 than in the empty chamber) and a preference for social novelty (spending more time in the chamber containing stranger 2 than in the chamber containing the now-familiar stranger 1). These social preferences were observed in both male and female mice, and in juveniles and adults. The exception was A/J, a strain that demonstrated a preference for the central chamber. Results are discussed in terms of potential applications of the new methods, and the proper controls for the interpretation of social behavior data, including assays for health, relevant sensory abilities and motor functions. This new standardized procedure to quantitate sociability and preference for social novelty in mice provides a method to assess tendencies for social avoidance in mouse models of autism.

https://onlinelibrary.wiley.com/doi/epdf/10.1111/j.1601-1848.2004.00076.x

Sociability and preference for social novelty in five inbred strains: an approach to assess autistic-like behavior in mice

Since autism was first recognized as a disorder in 1943, speculation about its aetiology has ranged from biological to psychological and back again. After twin studies during the 1970s and 1980s yielded unequivocal evidence for a genetic component, aetiological research in autism began to focus primarily on uncovering the genetic mechanisms involved. The identification of chromosomal abnormalities and Mendelian syndromes among individuals with autism, in conjunction with data from genome screens and candidate-gene studies, has helped to refine the view of the complex genetics that underlies autism spectrum conditions.

Genetics of autism: complex aetiology for a heterogeneous disorder.

While the primary language deficit in autism has been thought to be pragmatic, and in specific language impairment (SLI) structural, recent research suggests phenomenological and possibly genetic overlap between the two syndromes. To compare communicative competence in parents of children with autism, SLI, and down syndrome (DS), we used a modified pragmatic rating scale (PRS-M). Videotapes of conversational interviews with 47 autism, 47 SLI, and 21 DS parents were scored blind to group membership. Autism and SLI parents had significantly lower communication abilities than DS parents. Fifteen percent of the autism and SLI parents showed severe deficits. Our results suggest that impaired communication is part of the broader autism phenotype and a broader SLI phenotype, especially among male family members.

Communicative Competence in Parents of Children with Autism and Parents of Children with Specific Language Impairment

Reports of a relatively high prevalence of absolute pitch (AP) in autistic disorder suggest that AP is associated with some of the distinctive cognitive and social characteristics seen in autism spectrum disorders. Accordingly we examined cognition, personality, social behavior, and language in 13 musicians with strictly defined AP (APS) and 33 musician controls (MC) without AP using standardized interviews and tests previously applied to identify the broad autism phenotype seen in the relatives of autistic probands. These included the Pragmatic Rating Scale (PRS) (social aspects of language) the Personality Assessment Schedule (PAS) (rigidity, aloofness, anxiety/worry, hypersensitivity), and WAIS performance subtests (PIQ). On the basis of their behavior in the interviews, subjects were classified as socially eccentric, somewhat eccentric, or not eccentric. Forty-six percent of the APS, but only 15% of the MC, were classified as socially eccentric (p < .03). APS but not MC showed higher scores on block design than on the other PIQ tests (p < .06), a PIQ pattern seen in autism spectrum disorders. Although APS and MC did not differ significantly on other measures it is of note that APS mean scores on the PRS and PAS (5.69, 4.92) were almost twice as high as those for the MC (3.03, 2.45). Thus, musicians with AP show some of the personality, language, and cognitive features associated with autism. Piecemeal information processing, of which AP is an extreme and rare example, is characteristic of autism and may be associated as well with subclinical variants in language and behavior. We speculate that the gene or genes that underlie AP may be among the genes that contribute to autism.

Beth Rosen-Sheidley

Papers

Genetics of autism: complex aetiology for a heterogeneous disorder.

Communicative Competence in Parents of Children with Autism and Parents of Children with Specific Language Impairment

Autism-related language, personality, and cognition in people with absolute pitch: results of a preliminary study.