Autism-associated Variants Research Articles

Predicting Intervention Use in Youth with Rare Variants in Autism-Associated Genes.

Specialized multidisciplinary supports are important for long-term outcomes for autistic youth. Although family and child factors predict service utilization in autism, little is known with respect to youth with rare, autism-associated genetic variants, who frequently have increased psychiatric, developmental, and behavioral needs. We investigate the impact of family factors on service utilization to determine whether caregiver (autistic features, education, income) and child (autistic features, sex, age, IQ, co-occurring conditions) factors predicted service type (e.g., speech, occupational, behavioral) and intensity (hours/year) among children with autism-associated variants (N = 125), some of whom also had a confirmed ASD diagnosis. Analyses revealed variability in the types of services used across a range of child demographic, behavioral, and mental health characteristics. Speech therapy was the most received service (87.2%). Importantly, behavior therapy was the least received service and post-hoc analyses revealed that use of this therapy was uniquely predicted by ASD diagnosis. However, once children received a particular service, there was largely comparable intensity of services, independent of caregiver and child factors. Findings suggest that demographic and clinical factors impact families' ability to obtain services, with less impact on the intensity of services received. The low receipt of therapies that specifically address core support needs in autism (i.e., behavior therapy) indicates more research is needed on the availability of these services for youth with autism-associated variants, particularly for those who do not meet criteria for an ASD diagnosis but do demonstrate elevated and impactful child autistic features as compared to the general population.

In silico Gene Set and Pathway Enrichment Analyses Highlight Involvement of Ion Transport in Cholinergic Pathways in Autism: Rationale for Nutritional Intervention.

Food is the primary human source of choline, an essential precursor to the neurotransmitter acetylcholine, which has a central role in signaling pathways that govern sensorimotor functions. Most Americans do not consume their recommended amount of dietary choline, and populations with neurodevelopmental conditions like autism spectrum disorder (ASD) may be particularly vulnerable to consequences of choline deficiency. This study aimed to identify a relationship between ASD and cholinergic signaling through gene set enrichment analysis and interrogation of existing database evidence to produce a systems biology model. In gene set enrichment analysis, two gene ontologies were identified as overlapping for autism-related and for cholinergic pathways-related functions, both involving ion transport regulation. Subsequent modeling of ion transport intensive cholinergic signaling pathways highlighted the importance of two genes with autism-associated variants: GABBR1, which codes for the gamma aminobutyric acid receptor (GABAB1), and KCNN2, which codes for calcium-activated, potassium ion transporting SK2 channels responsible for membrane repolarization after cholinergic binding/signal transmission events. Cholinergic signal transmission pathways related to these proteins were examined in the Pathway Studio environment. The ion transport ontological associations indicated feasibility of a dietary choline support as a low-risk therapeutic intervention capable of modulating cholinergic sensory signaling in autism. Further research at the intersection of dietary status and sensory function in autism is warranted.

Autism-Associated Variant in the SLC6A3 Gene Alters the Oral Microbiome and Metabolism in a Murine Model.

Background: Altered dopamine (DA) signaling has been associated with autism spectrum disorder (ASD), a neurodevelopmental condition estimated to impact 1 in 54 children in the United States. There is growing evidence for alterations in both gastrointestinal function and oral microbiome composition in ASD. Recent work suggests that rare variants of the SLC6A3 gene encoding the DA transporter (DAT) identified in individuals with ASD result in structural and functional changes to the DAT. One such recently identified de novo mutation is a threonine to methionine substitution at position 356 of the DAT (DAT T356M). The DAT T356M variant is associated with ASD-like phenotypes in mice homozygous for the mutation (DAT T356M+/+), including social deficits, hyperactivity, and impaired DA signaling. Here, we determine the impact of this altered DA signaling as it relates to altered oral microbiota, and metabolic and gastrointestinal dysfunction.Methods: In the DAT T356M+/+ mouse, we determine the oral microbiota composition, metabolic function, and gastrointestinal (GI) function. We examined oral microbiota by 16S RNA sequencing. We measured metabolic function by examining glucose tolerance and we probed gastrointestinal parameters by measuring fecal dimensions and weight.Results: In the DAT T356M+/+ mouse, we evaluate how altered DA signaling relates to metabolic dysfunction and altered oral microbiota. We demonstrate that male DAT T356M+/+ mice weigh less (Wild type (WT) = 26.48 ± 0.6405 g, DAT T356M+/+ = 24.14 ± 0.4083 g) and have decreased body fat (WT = 14.89 ± 0.6206%, DAT T356M+/+ = 12.72 ± 0.4160%). These mice display improved glucose handling (WT = 32.60 ± 0.3298 kcal/g, DAT T356M+/+ = 36.97 ± 0.4910 kcal/g), and an altered oral microbiota. We found a significant decrease in Fusobacterium abundance. The abundance of Fusobacterium was associated with improved glucose handling and decreased body fat.Conclusions: Our findings provide new insights into how DAT dysfunction may alter gastrointestinal function, composition of the oral microbiota, and metabolism. Our data suggest that impaired DA signaling in ASD is associated with a number of metabolic and gastrointestinal changes which are common in individuals with ASD.

Autism-associated variants of neuroligin 4X impair synaptogenic activity by various molecular mechanisms

BackgroundSeveral genetic alterations, including point mutations and copy number variations in NLGN genes, have been associated with psychiatric disorders, such as autism spectrum disorder (ASD) and X-linked mental retardation (XLMR). NLGN genes encode neuroligin (NL) proteins, which are adhesion molecules that are important for proper synaptic formation and maturation. Previously, we and others found that the expression level of murine NL1 is regulated by proteolytic processing in a synaptic activity-dependent manner.MethodsIn this study, we analyzed the effects of missense variants associated with ASD and XLMR on the metabolism and function of NL4X, a protein which is encoded by the NLGN4X gene and is expressed only in humans, using cultured cells, primary neurons from rodents, and human induced pluripotent stem cell-derived neurons.ResultsNL4X was found to undergo proteolytic processing in human neuronal cells. Almost all NL4X variants caused a substantial decrease in the levels of mature NL4X and its synaptogenic activity in a heterologous culture system. Intriguingly, the L593F variant of NL4X accelerated the proteolysis of mature NL4X proteins located on the cell surface. In contrast, other variants decreased the cell-surface trafficking of NL4X. Notably, protease inhibitors as well as chemical chaperones rescued the expression of mature NL4X.LimitationsOur study did not reveal whether these dysfunctional phenotypes occurred in individuals carrying NLGN4X variant. Moreover, though these pathological mechanisms could be exploited as potential drug targets for ASD, it remains unclear whether these compounds would have beneficial effects on ASD model animals and patients.ConclusionsThese data suggest that reduced amounts of the functional NL4X protein on the cell surface is a common mechanism by which point mutants of the NL4X protein cause psychiatric disorders, although different molecular mechanisms are thought to be involved. Furthermore, these results highlight that the precision medicine approach based on genetic and cell biological analyses is important for the development of therapeutics for psychiatric disorders.

Journal Digest: Home Environment; Postpartum Mental Illness; Placebo in Psychedelic Study; Single Gene Mutation; Topiramate

Journal Digest: Home Environment; Postpartum Mental Illness; Placebo in Psychedelic Study; Single Gene Mutation; Topiramate

A Cluster of Autism-Associated Variants on X-Linked NLGN4X Functionally Resemble NLGN4Y

Autism spectrum disorder (ASD) is more prevalent in males; however, the etiology for this sex bias is not well understood. Many mutations on X-linked cell adhesion molecule NLGN4X result in ASD or intellectual disability. NLGN4X is part of an X-Y pair, with NLGN4Y sharing ∼97% sequence homology. Using biochemistry, electrophysiology, and imaging, we show that NLGN4Y displays severe deficits in maturation, surface expression, and synaptogenesis regulated by one amino acid difference with NLGN4X. Furthermore, we identify a cluster of ASD-associated mutations surrounding the critical amino acid in NLGN4X, and these mutations phenocopy NLGN4Y. We show that NLGN4Y cannot compensate for the functional deficits observed in ASD-associated NLGN4X mutations. Altogether, our data reveal a potential pathogenic mechanism for male bias in NLGN4X-associated ASD.

180 Analysis of a Hyperfunctional Autism-Associated Variant, Knockout, and Inhibition of the Serotonin Reuptake Transporter (SERT) in Mice Reveals That Enteric Nervous System Development, Gastrointestinal Motility, and Mucosal Homeostasis Are Highly Dependent on 5-HT, SERT, and 5-HT4 Receptors

180 Analysis of a Hyperfunctional Autism-Associated Variant, Knockout, and Inhibition of the Serotonin Reuptake Transporter (SERT) in Mice Reveals That Enteric Nervous System Development, Gastrointestinal Motility, and Mucosal Homeostasis Are Highly Dependent on 5-HT, SERT, and 5-HT4 Receptors

Does reverse transport of dopamine play a role in autism?

genetic variants affecting the reverse transport of DA might influence the risk of common, sporadic forms of autism remains open. It is now widely accepted that rare genetic variants could play an important role in susceptibility to common diseases. In light of Cartier et al.'s results, major resequencing efforts of the SLC6A3 and STX1A genes should be undertaken in large cohorts of individuals with autism, with significant insights into disease biology likely from these results. Another interesting implication of the work by Cartier and colleagues lies in unraveling the therapeutic potential of DA reverse transport in autism. Starting from the observation that rare autism-causing variants are associated with inhibition of reverse transport of DA, it could be hypothesized that psychostimulants may serve as a potential therapeutic aid in autism. Notably, not only have psychostimulants been suggested to be effective for ADHD-like symptoms in autism spectrumdisorderindividuals,buttheprevalenceratesoftheiruseinautism

Rare Autism-Associated Variants Implicate Syntaxin 1 (STX1 R26Q) Phosphorylation and the Dopamine Transporter (hDAT R51W) in Dopamine Neurotransmission and Behaviors

BackgroundSyntaxin 1 (STX1) is a presynaptic plasma membrane protein that coordinates synaptic vesicle fusion. STX1 also regulates the function of neurotransmitter transporters, including the dopamine (DA) transporter (DAT). The DAT is a membrane protein that controls DA homeostasis through the high-affinity re-uptake of synaptically released DA. MethodsWe adopt newly developed animal models and state-of-the-art biophysical techniques to determine the contribution of the identified gene variants to impairments in DA neurotransmission observed in autism spectrum disorder (ASD). OutcomesHere, we characterize two independent autism-associated variants in the genes that encode STX1 and the DAT. We demonstrate that each variant dramatically alters DAT function. We identify molecular mechanisms that converge to inhibit reverse transport of DA and DA-associated behaviors. These mechanisms involve decreased phosphorylation of STX1 at Ser14 mediated by casein kinase 2 as well as a reduction in STX1/DAT interaction. These findings point to STX1/DAT interactions and STX1 phosphorylation as key regulators of DA homeostasis. InterpretationWe determine the molecular identity and the impact of these variants with the intent of defining DA dysfunction and associated behaviors as possible complications of ASD.

Functional evaluation of autism-associated mutations in NHE9.

SummaryNHE9 (SLC9A9) is an endosomal cation/proton antiporter with orthologs in yeast and bacteria. Rare, missense substitutions in NHE9 are genetically linked with autism, but have not been functionally evaluated. Here we use evolutionary conservation analysis to build a model-structure of NHE9 based on the crystal structure of bacterial NhaA and use it to screen autism-associated variants in the human population first by phenotype complementation in yeast, followed by functional analysis in primary cortical astrocytes from mouse. NHE9-GFP localizes to recycling endosomes where it significantly alkalinizes luminal pH, elevates uptake of transferrin and the neurotransmitter glutamate, and stabilizes surface expression of transferrin receptor and GLAST transporter. In contrast, autism associated variants L236S, S438P and V176I lack function in astrocytes. Thus, we establish a neurobiological cell model of a candidate gene in autism. Loss of function mutations in NHE9 may contribute to autistic phenotype by modulating synaptic membrane protein expression and neurotransmitter clearance.

An Autism-Associated Variant of Epac2 Reveals a Role for Ras/Epac2 Signaling in Controlling Basal Dendrite Maintenance in Mice

Author SummaryA fundamental feature of a neuron is the morphology of its dendrites, which are the processes that receive and integrate synaptic signals from other neurons. Neurons in the mammalian cortex exhibit two distinct dendritic arbors: apical dendrites, which extend far from the cell body, and basal dendrites, which elaborate locally around the cell body. After development, neurons must actively maintain each of these dendritic arbors to sustain their specific connectivity. Because several neurological and neurodevelopmental disorders are associated with disruptions in dendritic morphology, it is crucial to understand the molecular mechanisms that regulate the process of active maintenance of dendritic arbors. We find that disruption of a particular molecular pathway, the Ras-Epac2 pathway, can result in dramatic simplification of basal, but not apical, dendritic arbors in both cultured neurons and in the intact mouse brain. We show that a mutant form of Epac2, identified in patients with autism, also impairs basal dendrite maintenance and disrupts its interaction with Ras. Our findings suggest that specific molecular pathways can regulate distinct dendritic regions, and that disease-related mutations can inform our understanding of the molecules that regulate important biological processes.