Early lysosome defects precede neurodegeneration with amyloid-ß and tau aggregation in NHE6-null rat brain.

Loss-of-function mutations in the X-linked endosomal Na+/H+ exchanger 6 (NHE6) cause Christianson syndrome in males. Christianson syndrome involves endosome dysfunction leading to early cerebellar degeneration, as well as later-onset cortical and subcortical neurodegeneration, potentially including tau deposition as reported in post-mortem studies. In addition, there is reported evidence of modulation of amyloid-ß levels in experimental models wherein NHE6 expression was targeted. We have recently shown that loss of NHE6 causes defects in endosome maturation and trafficking underlying lysosome deficiency in primary mouse neurons in vitro. For in vivo studies, rat models may have an advantage over mouse models for the study of neurodegeneration, as rat brain can demonstrate robust deposition of endogenously-expressed amyloid-ß and tau in certain pathological states. Mouse models generally do not show the accumulation of insoluble, endogenously-expressed (non-transgenic) tau or amyloid-ß. Therefore, to study neurodegeneration in Christianson syndrome and the possibility of amyloid-ß and tau pathology, we generated an NHE6-null rat model of Christianson syndrome using CRISPR-Cas9 genome-editing. Here, we present the sequence of pathogenic events in neurodegenerating NHE6-null male rat brains across the lifespan. NHE6-null rats demonstrated an early and rapid loss of Purkinje cells in the cerebellum, as well as a more protracted neurodegenerative course in the cerebrum. In both the cerebellum and cerebrum, lysosome deficiency is an early pathogenic event, preceding autophagic dysfunction. Microglial and astrocyte activation also occur early. In the hippocampus and cortex, lysosome defects precede loss of pyramidal cells. Importantly, we subsequently observed biochemical and in situ evidence of both amyloid-ß and tau aggregation in the aged NHE6-null hippocampus and cortex (but not in the cerebellum). Tau deposition is widely distributed, including cortical and subcortical distributions. Interestingly, we observed tau deposition in both neurons and glia, as has been reported in Christianson syndrome post-mortem studies previously. In summary, this experimental model is among very few examples of a genetically modified animal that exhibits neurodegeneration with deposition of endogenously-expressed amyloid-ß and tau. This NHE6-null rat will serve as a new robust model for Christianson syndrome. Furthermore, these studies provide evidence for linkages between endolysosome dysfunction and neurodegeneration involving protein aggregations, including amyloid-ß and tau. Therefore these studies may provide insight into mechanisms of more common neurodegenerative disorders, including Alzheimer's disease and related dementias.

Excessive Laughter-like Vocalizations, Microcephaly, and Translational Outcomes in the Ube3a Deletion Rat Model of Angelman Syndrome.

Angelman syndrome (AS) is a rare genetic neurodevelopmental disorder characterized by intellectual disabilities, motor and balance deficits, impaired communication, and a happy, excitable demeanor with frequent laughter. We sought to elucidate a preclinical outcome measure in male and female rats that addressed communication abnormalities of AS and other neurodevelopmental disorders in which communication is atypical and/or lack of speech is a core feature. We discovered, and herein report for the first time, excessive laughter-like 50 kHz ultrasonic emissions in the Ube3amat-/pat+ rat model of AS, which suggests an excitable, playful demeanor and elevated positive affect, similar to the demeanor of individuals with AS. Also in line with the AS phenotype, Ube3amat-/pat+ rats demonstrated aberrant social interactions with a novel partner, distinctive gait abnormalities, impaired cognition, an underlying LTP deficit, and profound reductions in brain volume. These unique, robust phenotypes provide advantages compared with currently available mouse models and will be highly valuable as outcome measures in the evaluation of therapies for AS.SIGNIFICANCE STATEMENT Angelman syndrome (AS) is a severe neurogenetic disorder for which there is no cure, despite decades of research using mouse models. This study used a recently developed rat model of AS to delineate disease-relevant outcome measures to facilitate therapeutic development. We found the rat to be a strong model of AS, offering several advantages over mouse models by exhibiting numerous AS-relevant phenotypes, including overabundant laughter-like vocalizations, reduced hippocampal LTP, and volumetric anomalies across the brain. These findings are unconfounded by detrimental motor abilities and background strain, issues plaguing mouse models. This rat model represents an important advancement in the field of AS, and the outcome metrics reported herein will be central to the therapeutic pipeline.

Imprinting effects of UBE3A loss on synaptic gene networks and Wnt signaling pathways.

Ubiquitin E3 ligase 3A (UBE3A) encodes an E3 ubiquitin ligase whose loss from the maternal allele causes the neurodevelopmental disorder Angelman syndrome (AS). Previous studies of UBE3A function have not examined full Ube3a deletion in mouse, the complexity of imprinted gene networks in brain nor the molecular basis of systems-level cognitive dysfunctions in AS. We therefore utilized a systems biology approach to elucidate how UBE3A loss impacts the early postnatal brain in a novel CRISPR/Cas9-engineered rat Angelman model of a complete Ube3a deletion. Strand-specific transcriptome analysis of offspring from maternally or paternally inherited Ube3a deletions revealed the expected parental expression patterns of Ube3a sense and antisense transcripts by postnatal day 2 (P2) in hypothalamus and day 9 (P9) in cortex, compared to wild-type littermates. The dependency of genome-wide effects on parent-of-origin, Ube3a genotype and time (P2 and P9) was investigated through transcriptome (RNA sequencing of cortex and hypothalamus) and methylome (whole-genome bisulfite sequencing of hypothalamus). Weighted gene co-expression and co-methylation network analyses identified co-regulated networks in maternally inherited Ube3a deletion offspring enriched in postnatal developmental processes including Wnt signaling, synaptic regulation, neuronal and glial functions, epigenetic regulation, ubiquitin, circadian entrainment and splicing. Furthermore, we showed that loss of the paternal Ube3a antisense transcript resulted in both unique and overlapping dysregulated gene pathways with maternal loss, predominantly at the level of differential methylation. Together, these results provide a holistic examination of the molecular impacts of UBE3A loss in brain, supporting the existence of interactive epigenetic networks between maternal and paternal transcripts at the Ube3a locus.

Neuronal overexpression of Ube3a isoform 2 causes behavioral impairments and neuroanatomical pathology relevant to 15q11.2-q13.3 duplication syndrome.

Maternally derived copy number gains of human chromosome 15q11.2-q13.3 (Dup15q syndrome or Dup15q) cause intellectual disability, epilepsy, developmental delay, hypotonia, speech impairments, and minor dysmorphic features. Dup15q syndrome is one of the most common and penetrant chromosomal abnormalities observed in individuals with autism spectrum disorder (ASD). Although ∼40 genes are located in the 15q11.2-q13.3 region, overexpression of the ubiquitin-protein E3A ligase (UBE3A) gene is thought to be the predominant molecular cause of the phenotypes observed in Dup15q syndrome. The UBE3A gene demonstrates maternal-specific expression in neurons and loss of maternal UBE3A causes Angelman syndrome, a neurodevelopmental disorder with some overlapping neurological features to Dup15q. To directly test the hypothesis that overexpression of UBE3A is an important underlying molecular cause of neurodevelopmental dysfunction, we developed and characterized a mouse overexpressing Ube3a isoform 2 in excitatory neurons. Ube3a isoform 2 is conserved between mouse and human and known to play key roles in neuronal function. Transgenic mice overexpressing Ube3a isoform 2 in excitatory forebrain neurons exhibited increased anxiety-like behaviors, learning impairments, and reduced seizure thresholds. However, these transgenic mice displayed normal social approach, social interactions, and repetitive motor stereotypies that are relevant to ASD. Reduced forebrain, hippocampus, striatum, amygdala, and cortical volume were also observed. Altogether, these findings show neuronal overexpression of Ube3a isoform 2 causes phenotypes translatable to neurodevelopmental disorders.

Unique Features of the Gut Microbiome Characterized in Animal Models of Angelman Syndrome.

A large subset of patients with Angelman syndrome (AS) suffer from concurrent gastrointestinal (GI) issues, including constipation, poor feeding, and reflux. AS is caused by the loss of ubiquitin ligase E3A (UBE3A) gene expression in the brain. Clinical features of AS, which include developmental delays, intellectual disability, microcephaly, and seizures, are primarily due to the deficient expression or function of the maternally inherited UBE3A allele. The association between neurodevelopmental delay and GI disorders is part of the increasing evidence suggesting a link between the brain and the gut microbiome via the microbiota-gut-brain axis. To investigate the associations between colonization of the gut microbiota in AS, we characterized the fecal microbiome in three animal models of AS involving maternal deletions of Ube3A, including mouse, rat, and pig, using 16S rRNA amplicon sequencing. Overall, we identified changes in bacterial abundance across all three animal models of AS. Specific bacterial groups were significantly increased across all animal models, including Lachnospiraceae Incertae sedis, Desulfovibrios sp., and Odoribacter, which have been correlated with neuropsychiatric disorders. Taken together, these findings suggest that specific changes to the local environment in the gut are driven by a Ube3a maternal deletion, unaffected by varying housing conditions, and are prominent and detectable across multiple small and large animal model species. These findings begin to uncover the underlying mechanistic causes of GI disorders in AS patients and provide future therapeutic options for AS patients. IMPORTANCE Angelman syndrome (AS)-associated gastrointestinal (GI) symptoms significantly impact quality of life in patients. In AS models in mouse, rat, and pig, AS animals showed impaired colonization of the gut microbiota compared to wild-type (healthy) control animals. Common changes in AS microbiomes across all three animal models may play a causal effect for GI symptoms and may help to identify ways to treat these comorbidities in patients in the future.

Gait as a quantitative translational outcome measure in Angelman syndrome.

Angelman syndrome (AS) is a genetic neurodevelopmental disorder characterized by developmental delay, lack of speech, seizures, intellectual disability, hypotonia, and motor coordination deficits. Motor abilities are an important outcome measure in AS as they comprise a broad repertoire of metrics including ataxia, hypotonia, delayed ambulation, crouched gait, and poor posture, and motor dysfunction affects nearly every individual with AS. Guided by collaborative work with AS clinicians studying gait, the goal of this study was to perform an in-depth gait analysis using the automated treadmill assay, DigiGait. Our hypothesis is that gait presents a strong opportunity for a reliable, quantitative, and translational metric that can serve to evaluate novel pharmacological, dietary, and genetic therapies. In this study, we used an automated gait analysis system, in addition to standard motor behavioral assays, to evaluate components of motor, exploration, coordination, balance, and gait impairments across the lifespan in an AS mouse model. Our study demonstrated marked global motoric deficits in AS mice, corroborating previous reports. Uniquely, this is the first report of nuanced aberrations in quantitative spatial and temporal components of gait in AS mice compared to sex- and age-matched wildtype littermates followed longitudinally using metrics that are analogous in AS individuals. Our findings contribute evidence toward the use of nuanced motor outcomes (i.e., gait) as valuable and translationally powerful metrics for therapeutic development for AS, as well as other genetic neurodevelopmental syndromes. LAY SUMMARY: Movement disorders affect nearly every individual with Angelman Syndrome (AS). The most common motor problems include spasticity, ataxia of gait (observed in the majority of ambulatory individuals), tremor, and muscle weakness. This report focused on quantifying various spatial and temporal aspects of gait as a reliable, translatable outcome measure in a preclinical AS model longitudinally across development. By increasing the number of translational, reliable, functional outcome measures in our wheelhouse, we will create more opportunities for identifying and advancing successful medical interventions.

Insulin-like growth factor-2 does not improve behavioral deficits in mouse and rat models of Angelman Syndrome.

BACKGROUND: Angelman Syndrome (AS) is a rare neurodevelopmental disorder for which there is currently no cure or effective therapeutic. Since the genetic cause of AS is known to be dysfunctional expression of the maternal allele of ubiquitin protein ligase E3A (UBE3A), several genetic animal models of AS have been developed. Both the Ube3a maternal deletion mouse and rat models of AS reliably demonstrate behavioral phenotypes of relevance to AS and therefore offer suitable in vivo systems in which to test potential therapeutics. One promising candidate treatment is insulin-like growth factor-2 (IGF-2), which has recently been shown to ameliorate behavioral deficits in the mouse model of AS and improve cognitive abilities across model systems. METHODS: We used both the Ube3a maternal deletion mouse and rat models of AS to evaluate the ability of IGF-2 to improve electrophysiological and behavioral outcomes. RESULTS: Acute systemic administration of IGF-2 had an effect on electrophysiological activity in the brain and on a metric of motor ability; however the effects were not enduring or extensive. Additional metrics of motor behavior, learning, ambulation, and coordination were unaffected and IGF-2 did not improve social communication, seizure threshold, or cognition. LIMITATIONS: The generalizability of these results to humans is difficult to predict and it remains possible that dosing schemes (i.e., chronic or subchronic dosing), routes, and/or post-treatment intervals other than that used herein may show more efficacy. CONCLUSIONS: Despite a few observed effects of IGF-2, our results taken together indicate that IGF-2 treatment does not profoundly improve behavioral deficits in mouse or rat models of AS. These findings shed cautionary light on the potential utility of acute systemic IGF-2 administration in the treatment of AS.

The Effects of Chronic Exposure to Ambient Traffic-Related Air Pollution on Alzheimer's Disease Phenotypes in Wildtype and Genetically Predisposed Male and Female Rats.

BACKGROUND: Epidemiological data link traffic-related air pollution (TRAP) to increased risk of Alzheimer's disease (AD). Preclinical data corroborating this association are largely from studies of male animals exposed acutely or subchronically to high levels of isolated fractions of TRAP. What remains unclear is whether chronic exposure to ambient TRAP modifies AD risk and the influence of sex on this interaction. OBJECTIVES: This study sought to assess effects of chronic exposure to ambient TRAP on the time to onset and severity of AD phenotypes in a preclinical model and to determine whether sex or genetic susceptibility influences outcomes. METHODS: Male and female TgF344-AD rats that express human AD risk genes and wildtype littermates were housed in a vivarium adjacent to a heavily trafficked tunnel in Northern California and exposed for up to 14 months to filtered air (FA) or TRAP drawn from the tunnel and delivered to animals unchanged in real time. Refractive particles in the brain and AD phenotypes were quantified in 3-, 6-, 10-, and 15-month-old animals using hyperspectral imaging, behavioral testing, and neuropathologic measures. RESULTS: Particulate matter (PM) concentrations in TRAP exposure chambers fluctuated with traffic flow but remained below 24-h PM with aerodynamic diameter less than or equal to 2.5 micrometers (PM2.5) U.S. National Ambient Air Quality Standards limits. Ultrafine PM was a predominant component of TRAP. Nano-sized refractive particles were detected in the hippocampus of TRAP animals. TRAP-exposed animals had more amyloid plaque deposition, higher hyperphosphorylated tau levels, more neuronal cell loss, and greater cognitive deficits in an age-, genotype-, and sex-dependent manner. TRAP-exposed animals also had more microglial cell activation, but not astrogliosis. DISCUSSION: These data demonstrate that chronic exposure to ambient TRAP promoted AD phenotypes in wildtype and genetically susceptible rats. TRAP effects varied according to age, sex, and genotype, suggesting that AD progression depends on complex interactions between environment and genetics. These findings suggest current PM2.5 regulations are insufficient to protect the aging brain. https://doi.org/10.1289/EHP8905.

Sex-specific acute and chronic neurotoxicity of acute diisopropylfluorophosphate (DFP)-intoxication in juvenile Sprague-Dawley rats.

Preclinical efforts to improve medical countermeasures against organophosphate (OP) chemical threat agents have largely focused on adult male models. However, age and sex have been shown to influence the neurotoxicity of repeated low-level OP exposure. Therefore, to determine the influence of sex and age on outcomes associated with acute OP intoxication, postnatal day 28 Sprague-Dawley male and female rats were exposed to the OP diisopropylfluorophosphate (DFP; 3.4 mg/kg, s.c.) or an equal volume of vehicle (∼80 µL saline, s.c.) followed by atropine sulfate (0.1 mg/kg, i.m.) and pralidoxime (2-PAM; 25 mg/kg, i.m.). Seizure activity was assessed during the first 4 h post-exposure using behavioral criteria and electroencephalographic (EEG) recordings. At 1 d post-exposure, acetylcholinesterase (AChE) activity was measured in cortical tissue, and at 1, 7, and 28 d post-exposure, brains were collected for neuropathologic analyses. At 1 month post-DFP, animals were analyzed for motor ability, learning and memory, and hippocampal neurogenesis. Acute DFP intoxication triggered more severe seizure behavior in males than females, which was supported by EEG recordings. DFP caused significant neurodegeneration and persistent microglial activation in numerous brain regions of both sexes, but astrogliosis occurred earlier and was more severe in males compared to females. DFP males and females exhibited pronounced memory deficits relative to sex-matched controls. In contrast, acute DFP intoxication altered hippocampal neurogenesis in males, but not females. These findings demonstrate that acute DFP intoxication triggers seizures in juvenile rats of both sexes, but the seizure severity varies by sex. Some, but not all, chronic neurotoxic outcomes also varied by sex. The spatiotemporal patterns of neurological damage suggest that microglial activation may be a more important factor than astrogliosis or altered neurogenesis in the pathogenesis of cognitive deficits in juvenile rats acutely intoxicated with OPs.

Translational outcomes relevant to neurodevelopmental disorders following early life exposure of rats to chlorpyrifos.

BACKGROUND: Neurodevelopmental disorders (NDDs), including intellectual disability, attention deficit hyperactivity disorder (ADHD), and autism spectrum disorder (ASD), are pervasive, lifelong disorders for which pharmacological interventions are not readily available. Substantial increases in the prevalence of NDDs over a relatively short period may not be attributed solely to genetic factors and/or improved diagnostic criteria. There is now a consensus that multiple genetic loci combined with environmental risk factors during critical periods of neurodevelopment influence NDD susceptibility and symptom severity. Organophosphorus (OP) pesticides have been identified as potential environmental risk factors. Epidemiological studies suggest that children exposed prenatally to the OP pesticide chlorpyrifos (CPF) have significant mental and motor delays and strong positive associations for the development of a clinical diagnosis of intellectual delay or disability, ADHD, or ASD. METHODS: We tested the hypothesis that developmental CPF exposure impairs behavior relevant to NDD phenotypes (i.e., deficits in social communication and repetitive, restricted behavior). Male and female rat pups were exposed to CPF at 0.1, 0.3, or 1.0 mg/kg (s.c.) from postnatal days 1-4. RESULTS: These CPF doses did not significantly inhibit acetylcholinesterase activity in the blood or brain but significantly impaired pup ultrasonic vocalizations (USV) in both sexes. Social communication in juveniles via positive affiliative 50-kHz USV playback was absent in females exposed to CPF at 0.3 mg/kg and 1.0 mg/kg. In contrast, this CPF exposure paradigm had no significant effect on gross locomotor abilities or contextual and cued fear memory. Ex vivo magnetic resonance imaging largely found no differences between the CPF-exposed rats and the corresponding vehicle controls using strict false discovery correction; however, there were interesting trends in females in the 0.3 mg/kg dose group. CONCLUSIONS: This work generated and characterized a rat model of developmental CPF exposure that exhibits adverse behavioral phenotypes resulting from perinatal exposures at levels that did not significantly inhibit acetylcholinesterase activity in the brain or blood. These data suggest that current regulations regarding safe levels of CPF need to be reconsidered.

Developmental exposure to near roadway pollution produces behavioral phenotypes relevant to neurodevelopmental disorders in juvenile rats.

Epidemiological studies consistently implicate traffic-related air pollution (TRAP) and/or proximity to heavily trafficked roads as risk factors for developmental delays and neurodevelopmental disorders (NDDs); however, there are limited preclinical data demonstrating a causal relationship. To test the effects of TRAP, pregnant rat dams were transported to a vivarium adjacent to a major freeway tunnel system in northern California where they were exposed to TRAP drawn directly from the face of the tunnel or filtered air (FA). Offspring remained housed under the exposure condition into which they were born and were tested in a variety of behavioral assays between postnatal day 4 and 50. To assess the effects of near roadway exposure, offspring of dams housed in a standard research vivarium were tested at the laboratory. An additional group of dams was transported halfway to the facility and then back to the laboratory to control for the effect of potential transport stress. Near roadway exposure delayed growth and development of psychomotor reflexes and elicited abnormal activity in open field locomotion. Near roadway exposure also reduced isolation-induced 40-kHz pup ultrasonic vocalizations, with the TRAP group having the lowest number of call emissions. TRAP affected some components of social communication, evidenced by reduced neonatal pup ultrasonic calling and altered juvenile reciprocal social interactions. These findings confirm that living in close proximity to highly trafficked roadways during early life alters neurodevelopment.

Generation of a Novel Rat Model of Angelman Syndrome with a Complete Ube3a Gene Deletion.

Angelman syndrome (AS) is a rare genetic disorder characterized by severe intellectual disability, seizures, lack of speech, and ataxia. The gene responsible for AS was identified as Ube3a and it encodes for E6AP, an E3 ubiquitin ligase. Currently, there is very little known about E6AP's mechanism of action in vivo or how the lack of this protein in neurons may contribute to the AS phenotype. Elucidating the mechanistic action of E6AP would enhance our understanding of AS and drive current research into new avenues that could lead to novel therapeutic approaches that target E6AP's various functions. To facilitate the study of AS, we have generated a novel rat model in which we deleted the rat Ube3a gene using CRISPR. The AS rat phenotypically mirrors human AS with loss of Ube3a expression in the brain and deficits in motor coordination as well as learning and memory. This model offers a new avenue for the study of AS. Autism Res 2020, 13: 397-409. © 2020 International Society for Autism Research,Wiley Periodicals, Inc. LAY SUMMARY: Angelman syndrome (AS) is a rare genetic disorder characterized by severe intellectual disability, seizures, difficulty speaking, and ataxia. The gene responsible for AS was identified as UBE3A, yet very little is known about its function in vivo or how the lack of this protein in neurons may contribute to the AS phenotype. To facilitate the study of AS, we have generated a novel rat model in which we deleted the rat Ube3a gene using CRISPR. The AS rat mirrors human AS with loss of Ube3a expression in the brain and deficits in motor coordination as well as learning and memory. This model offers a new avenue for the study of AS.

Developmental social communication deficits in the Shank3 rat model of phelan-mcdermid syndrome and autism spectrum disorder.

Mutations in the SHANK3 gene have been discovered in autism spectrum disorder (ASD), and the intellectual disability, Phelan-McDermid Syndrome. This study leveraged a new rat model of Shank3 deficiency to assess complex behavioral phenomena, unique to rats, which display a richer social behavior repertoire than mice. Uniquely detectable emissions of ultrasonic vocalizations (USV) in rats serve as situation-dependent affective signals and accomplish important communicative functions. We report, for the first time, a call and response acoustic playback assay of bidirectional social communication in juvenile Shank3 rats. Interestingly, we found that Shank3-deficient null males did not demonstrate the enhanced social approach behavior typically exhibited following playback of pro-social USV. Concomitantly, we discovered that emission of USV in response to playback was not genotype-dependent and emitted response calls were divergent in meaning. This is the first report of these socially relevant responses using a genetic model of ASD. A comprehensive and empirical analysis of vigorous play during juvenile reciprocal social interactions further revealed fewer bouts and reduced durations of time spent playing by multiple key parameters, including reduced anogenital sniffing and allogrooming. We further discovered that male null Shank3-deficient pups emitted fewer isolation-induced USV than Shank3 wildtype controls. Postnatal whole brain anatomical phenotyping was applied to visualize anatomical substrates that underlie developmental phenotypes. The data presented here lend support for the important role of Shank3 in social communication, the core symptom domain of ASD. By increasing the number of in vivo functional outcome measures, we improved the likelihood for identifying and moving forward with medical interventions. Autism Res 2018, 11: 587-601. © 2018 International Society for Autism Research, Wiley Periodicals, Inc. LAY SUMMARY: Clinically relevant outcomes are required to demonstrate the utility of therapeutics. We introduce findings in a rat model, and assess the impact of mutations in Shank3, an autism risk gene. We found that males with deficient expression of Shank3 did not demonstrate typical responses in a bi-directional social communication test and that social interaction was lower on key parameters. Outcome measures reported herein extend earlier results in mice and capture responses to acoustic calls, which is analogous to measuring receptive and expressive communication.

Touchscreen learning deficits and normal social approach behavior in the Shank3B model of Phelan-McDermid Syndrome and autism.

SHANK3 is a synaptic scaffolding protein localized in the postsynaptic density and has a crucial role in synaptogenesis and neural physiology. Deletions and point mutations in SHANK3 cause Phelan-McDermid Syndrome (PMS), and have also been implicated in autism spectrum disorder (ASD) and intellectual disabilities, leading to the hypothesis that reduced SHANK3 expression impairs basic brain functions that are important for social communication and cognition. Several mouse models of Shank3 deletions have been generated, varying in the specific domain deleted. Here we report impairments in cognitive function in mice heterozygous for exon 13-16 (coding for the PDZ domain) deletion. The touchscreen pairwise discrimination task was chosen by virtue of its: (a) conceptual and technical similarities to the Cambridge Neuropsychological Test Automated Battery (CANTAB) and NIH Toolbox Cognition Battery used for testing cognitive functions in humans, (b) minimal demand on motor abilities, and (c) capability to measure many aspects of learning and memory and complex cognitive functions, including cognitive flexibility. The similarity between our mouse tasks and human cognitive assays means a high translational validity in future intervention studies using preclinical models. Our study revealed that Shank3B heterozygous mice (+/-) were slower to reach criterion in the pairwise visual discrimination task, and exhibited trends toward making more errors (first trial errors) and more correction errors than wildtype mice (+/+). Open field activity was normal in +/-, ruling out hypo- or hyperactivity as potential confounds in the touchscreen test. Sociability in the three chamber test was also normal in both +/+ and +/-. These results indicate a deficit in discrimination learning in the Shank3B model of PMS and ASD, suggesting that this mouse model is a useful preclinical tool for studying neurobiological mechanisms behind cognitive impairments in PMS and ASD. The current findings are the starting point for our future research in which we will investigate multiple domains of cognition and explore pharmacological interventions.