Drug development for neurodevelopmental disorders: lessons learned from fragile X syndrome

ErbB inhibition rescues nigral dopamine neuron hyperactivity and repetitive behaviors in a mouse model of fragile X syndrome

Repetitive stereotyped behaviors are core symptoms of autism spectrum disorders (ASD) and fragile X syndrome (FXS), the prevalent genetic cause of intellectual disability and autism. The nigrostriatal dopamine (DA) circuit rules movement and creation of habits and sequential behaviors; therefore, its dysregulation could promote autistic repetitive behaviors. Nevertheless, inspection of substantia nigra pars compacta (SNpc) DA neurons in ASD models has been overlooked and specific evidence of their altered activity in ASD and FXS is absent. Here, we show that hyperactivity of SNpc DA neurons is an early feature of FXS. The underlying mechanism relies on an interplay between metabotropic glutamate receptor 1 (mGluR1) and ErbB tyrosine kinases, receptors for the neurotrophic and differentiation factors known as neuregulins. Up-regulation of ErbB4 and ErbB2 in nigral DA neurons drives neuronal hyperactivity and repetitive behaviors of the FXS mouse, concurrently rescued by ErbB inhibition. In conclusion, beyond providing the first evidence that nigral DA neuron hyperactivity is a signature of FXS and nigral mGluR1 and ErbB4/2 play a relevant role in FXS etiology, we demonstrate that inhibiting ErbB is a valuable pharmacological approach to attenuate stereotyped repetitive behaviors, thus opening an avenue toward innovative therapies for ASD and FXS treatment.

Synaptic disturbance in neurodevelopmental disorders: Perspectives from fragile X and Rett syndromes

Neurodevelopmental disorders (NDDs) are often referred to as "synaptopathies" because many of their behavioral symptoms arise from impaired synaptic development and function. However, the mechanisms that connect synaptic dysfunction to neurological symptoms remain unclear, mainly due to the wide variety of genetic and environmental factors involved in these disorders. Fragile X syndrome and Rett syndrome, two extensively studied monogenic NDDs, provide a unique opportunity to explore these mechanisms at molecular, cellular, and synaptic levels. This review summarizes the current understanding of how synaptic alterations contribute to the neurological symptoms observed in fragile X and Rett syndromes. A comparison of findings from mouse models indicates that an imbalance in local and distal connectivity may serve as a common feature of both disorders.

A Blueprint for Translational Precision Medicine in Autism Spectrum Disorder and Related Neurogenetic Syndromes

Objectives: Despite growing knowledge of the underlying neurobiology of autism spectrum disorder (ASD) and related neurogenetic syndromes, treatment discovery has remained elusive. In this review, we provide a blueprint for translational precision medicine in ASD and related neurogenetic syndromes. Methods: The discovery of trofinetide for Rett syndrome (RTT) is described, and the role of nonmammalian, mammalian, and stem cell model systems in the identification of molecular targets and drug screening is discussed. We then provide a framework for translating preclinical findings to human clinical trials, including the role of biomarkers in selecting molecular targets and evaluating target engagement, and discuss how to leverage these findings for future ASD drug development. Results: Multiple preclinical model systems for ASD have been developed, each with tradeoffs with regard to suitability for high-throughput small molecule screening, conservation across species, and behavioral face validity. Future clinical trials should incorporate biomarkers and intermediate phenotypes to demonstrate target engagement. Factors that contributed to the approval of trofinetide for RTT included replicated findings in mouse models, a well-studied natural history of the syndrome, development of RTT-specific outcome measures, and strong engagement of the RTT family community. Conclusions: The translation of our growing understanding of the neurobiology of ASD to human drug discovery will require a precision medicine approach, including the use of multiple model systems for molecular target selection, evaluation of target engagement, and clinical trial design strategies that address heterogeneity, power, and the placebo response.

A human electrophysiological biomarker of Fragile X Syndrome is shared in V1 of Fmr1 KO mice and caused by loss of FMRP in cortical excitatory neurons

Predicting clinical therapeutic outcomes from preclinical animal studies remains an obstacle to developing treatments for neuropsychiatric disorders. Electrophysiological biomarkers analyzed consistently across species could bridge this divide. In humans, alpha oscillations in the resting state electroencephalogram (rsEEG) are altered in many disorders, but these disruptions have not yet been characterized in animal models. Here, we employ a uniform analytical method to show in males with fragile X syndrome (FXS) that the slowed alpha oscillations observed in adults are also present in children and in visual cortex of adult and juvenile Fmr1 -/y mice. We find that alpha-like oscillations in mice reflect the differential activity of two classes of inhibitory interneurons, but the phenotype is caused by deletion of Fmr1 specifically in cortical excitatory neurons. These results provide a framework for studying alpha oscillation disruptions across species, advance understanding of a critical rsEEG signature in the human brain and inform the cellular basis for a putative biomarker of FXS.

Untangling the Molecular Mechanisms Contributing to Autism Spectrum Disorder Using Stem Cells

Autism spectrum disorder (ASD) is a complex neuro developmental condition characterized by significant genetic and phenotypic variability, making diagnosis and treatment challenging. The heterogeneity of ASD-associated genetic variants and the absence of clear causal factors in many cases complicate personalized care. Traditional models, such as postmortem brain tissue and animal studies, have provided valuable insights but are limited in capturing the dynamic processes and human-specific aspects of ASD pathology. Recent advances in human induced pluripotent stem cell (iPSC) technology have transformed ASD research by enabling the generation of patient-derived neural cells in both two-dimensional cultures and three-dimensional brain organoid models. These models retain the donor's genetic background, allowing researchers to investigate disease-specific cellular and molecular mechanisms while identifying potential therapeutic targets tailored to individual patients. This commentary highlights how stem cell-based approaches are advancing our understanding of ASD and paving the way for more personalized diagnostic and therapeutic strategies.

Trinucleotide repeat expansion and RNA dysregulation in fragile X syndrome: emerging therapeutic approaches

Fragile X syndrome (FXS) is characterized by intellectual impairment caused by CGG repeat expansion in the FMR1 gene. When repeats exceed 200, they induce DNA methylation of the promoter and the repeat region, resulting in transcriptional silencing of the FMR1 gene and the subsequent loss of FMRP protein. In the past decade or so, research has focused on the role of FMRP as an RNA-binding protein involved in translation inhibition in the brain in FXS model mice, particularly by slowing or stalling ribosome translocation on mRNA. More recent advances have shown that FMRP has a profound role in RNA splicing, at least in some cases by modulating the translation of splicing factor mRNAs. In a surprise, the human FMR1 gene is transcribed in most cases even with a full CGG expansion. However, much of the FMR1 that is produced is misspliced, which can be corrected by splice-switching antisense oligonucleotide (ASO) administration. Other recent findings suggest that inhibition of multiple kinases can demethylate the FMR1 gene and induce the formation of an R-loop in the CGG repeat region, leading to contraction of the repeat and FMRP restoration. These insights are paving the way for possible future therapeutic approaches for this disorder. We highlight the importance of FMRP restoration by ASO-mediated splice switching or CGG repeat modulation as key advances that may lead to successful treatments for FXS.

The Aberrant Behavior Checklist for Fragile X Syndrome: A Qualitative Clinician Evaluation of Content Validity

Objective: The current intense period of drug development for fragile X syndrome (FXS) and other neurodevelopmental disorders (NDDs) indications has highlighted the importance of behavioral outcome measures with strong psychometric properties and specifically content validity. The Aberrant Behavior Checklist-Community Edition (ABC-C), which has successfully been applied to autism spectrum disorder drug trials, has been revised for FXS (ABCFX) and is widely used for both clinical and research purposes. Despite its strong psychometric validation, the ABCFX and its parent measure have not been subjected to qualitative content validity evaluations. The present study intended to fill this gap. Methods: Using two surveys administered sequentially and developed with guidance and review from the Food and Drug Administration (FDA), we asked 10 clinicians experienced in FXS and related NDDs to determine the adequacy of the ABCFX for assessing its behavioral constructs, its relevance to FXS, and its potential for detecting response to interventions. Various descriptive statistic parameters and ad hoc metrics were used to analyze categorical and Likert-like scale responses. Results: Experts considered that most items and all six ABCFX subscales indeed evaluated their explicit or implicit behavioral constructs. However, item and subscale specificity were relatively low (∼25%-30%). Relevance of items of the Hyperactivity subscale was relatively high while low for many items of the Socially Unresponsive/Lethargic subscale. These items were also considered of low responsiveness potential. Irritability, Hyperactivity, Stereotypy, and Social Avoidance were the subscales with the strongest profiles, although the experts estimated that Stereotypy items may not be that responsive to treatment. A novel Anxiety construct, representing mainly recently reported observable behaviors, contributed mainly by Irritability items, emerged as a potential measure. Conclusions: The present study demonstrated the overall adequacy of the ABCFX for its behavioral constructs, its relevance to FXS, and its potential for detecting response to treatment. It also showed that anxiety, a distinctive feature of FXS and other genetic NDDs, can also be measured by the ABCFX. These findings can help with the implementation and interpretation of the ABCFX, as well as with potential improvements to the measure in FXS and other NDDs.

An iPSC model of fragile X syndrome reflects clinical phenotypes and reveals m 6 A- mediated epi-transcriptomic dysregulation underlying synaptic dysfunction

Fragile X syndrome (FXS), the leading genetic cause of intellectual disability, arises from FMR1 gene silencing and loss of the FMRP protein. N6-methyladenosine (m 6 A) is a prevalent mRNA modification essential for post-transcriptional regulation. FMRP is known to bind to and regulate the stability of m 6 A-containing transcripts. However, how loss of FMRP impacts on transcriptome-wide m 6 A modifications in FXS patients remains unknown. To answer this question, we generated cortical neurons differentiated from induced pluripotent stem cells (iPSC) derived from healthy subjects and FXS patients. In electrophysiology recordings, we validated that synaptic and neuronal network defects in iPSC-derived FXS neurons corresponded to the clinical EEG data of the patients from which the corresponding iPSC line was derived. In analysis of transcriptome-wide methylation, we show that FMRP deficiency led to increased translation of m 6 A writers, resulting in hypermethylation that primarily affecting synapse-associated transcripts and increased mRNA decay. Conversely, in the presence of an m 6 A writer inhibitor, synaptic defects in FXS neurons were rescued. Taken together, our findings uncover that an FMRP-dependent epi-transcriptomic mechanism contributes to FXS pathogenesis by disrupting m 6 A modifications in FXS, suggesting a promising avenue for m 6 A- targeted therapies.

Systematic Review: Fragile X Syndrome Across the Lifespan with a Focus on Genetics, Neurodevelopmental, Behavioral and Psychiatric Associations

BACKGROUND/OBJECTIVES

Fragile X syndrome (FXS) is one of the most common genetic causes of intellectual developmental disability and autism spectrum disorder (ASD), second only to Down's syndrome and associated with a broad range of neurodevelopmental, behavioral, and psychiatric challenges. FXS may be present in infants or young children with characteristic dysmorphic features, developmental delays, and behavioral challenges. The diagnosis of FXS is confirmed by the molecular genetic testing of the FMR1 gene encoding fragile X messenger RNA-binding protein (FMRP), involved in regulating the translation of multiple mRNAs which play a key role in neuronal development and synaptic plasticity. Understanding the genetic cause, pathophysiology, and natural history of FXS is crucial for identifying commonly associated comorbidities, instituting effective therapeutic interventions, and improving long-term outcomes.

METHODS

This systematic review employed a comprehensive literature search using multiple electronic databases including PubMed, Web of Science, and Scopus with keywords related to fragile X syndrome, lifespan, genetics, neurodevelopmental, behavioral, and psychiatric disorders.

RESULTS

FXS is associated with an increased risk for specific neurodevelopmental, or psychiatric disorders. Symptoms and challenges associated with FXS vary based on multiple factors, including genetic differences, age, sex, comorbid conditions, various environmental influences, the availability of support, and opportunities for therapeutic interventions. Knowledge of these associations helps guide caregivers and clinicians in identifying potentially treatable conditions that can help to improve the lives of affected patients and their families.

CONCLUSIONS

The focus of this article is to explore and describe the genetic underpinnings of FXS, identify associated developmental, behavioral, and psychiatric conditions over the lifespan, and provide a review of clinical features, therapeutic interventions including investigational treatments, and current research updates.

Role of peroxisome proliferator-activated receptors α and γ in mediating the beneficial effects of β-caryophyllene in a rat model of fragile X syndrome

β-Caryophyllene (BCP) is a naturally occurring sesquiterpene found in numerous plant species, including Cannabis sativa. BCP has shown a high safety profile and a wide range of biological functions, including beneficial effects in neurodegenerative and inflammatory diseases. Here, we used behavioral, pharmacological, and in-silico docking analyses to investigate the effects and mechanism of action of BCP in Fragile X Syndrome (FXS), the most common inherited cause of Autism Spectrum Disorder (ASD) and intellectual disability. To this aim, we used the recently validated Fmr1-Δexon 8 rat model of FXS, that is also a genetic rat model of ASD. Acute and repeated oral administration of BCP rescued the cognitive deficits displayed by Fmr1-Δexon 8 rats, without inducing tolerance after repeated administration. These beneficial effects were mediated by activation of hippocampal peroxisome proliferator-activated receptors (PPARs) α and γ, and were mimicked by the PPARα agonist Fenofibrate and the PPARγ agonist Pioglitazone. Conversely, CB2 cannabinoid receptors were not involved. Docking analyses further confirmed the ability of BCP to bind rat PPARs. Together, our findings demonstrate that hippocampal PPARs α and γ play a role in the cognitive deficits observed in a rat model of FXS, and provide first preclinical evidence about the efficacy and mechanism of action of BCP in neurodevelopmental disorders.

Discovery of MDI-114215: A Potent and Selective LIMK Inhibitor To Treat Fragile X Syndrome

LIMKs are serine/threonine and tyrosine kinases responsible for controlling cytoskeletal dynamics as key regulators of actin stability, ensuring synaptic health through normal synaptic bouton structure and function. However, LIMK1 overactivation results in abnormal dendritic synaptic development that characterizes the pathogenesis of Fragile X Syndrome (FXS). As a result, the development of LIMK inhibitors represents an emerging disease-modifying therapeutic approach for FXS. We report the discovery of MDI-114215 (85), a novel, potent allosteric dual-LIMK1/2 inhibitor that demonstrates exquisite kinome selectivity. 85 reduces phospho-cofilin in mouse brain slices and rescues impaired hippocampal long-term potentiation in brain slices from FXS mice. We also show that LIMK inhibitors are effective in reducing phospho-cofilin levels in iPSC neurons derived from FXS patients, demonstrating 85 to be a potential therapeutic candidate for FXS that could have broad application to neurological disorders or cancers caused by LIMK1/2 overactivation and actin instability.

Clinically-probed mechanisms of action in Fragile-X syndrome fail to normalize translational EEG phenotypes in Fmr1 knockout mice

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by Fragile X Messenger Ribonucleoprotein (FMRP) deficiency. Electroencephalogram (EEG) changes in FXS include alterations of oscillatory activity and responses to sensory stimuli, some of which have been back-translated into rodent models by knocking-out the Fragile X messenger ribonucleoprotein 1 gene (Fmr1-KO). However, the validity of these EEG phenotypes as objective biomarkers requires further investigation. Potential pharmacotherapies such as mGluR5 inhibitors (e.g. CTEP; 2-chloro-4-((2,5-dimethyl-1-(4-(trifluoromethoxy)phenyl)-1H-imidazole-4-yl)ethynyl)pyridine), GABABR agonists (e.g. arbaclofen) and δ-containing GABAAR agonists (e.g. gaboxadol) have not translated into clinical success despite rescuing many phenotypes in the Fmr1-KO model. Yet none of these treatments have been assessed on EEG phenotypes in the Fmr1-KO model. Therefore, we set out to discover new EEG phenotypes in Fmr1-KO mice, using "task-free" and auditory-evoked (AEPs) and visually-evoked potential (VEP) paradigms, and probe their modulation by CTEP, arbaclofen and gaboxadol, using within-subjects designs. First, we report Fmr1-KO-associated EEG abnormalities that closely resemble those observed in FXS, including elevated gamma-band power, reduced alpha/beta-band coherence, increased AEPs and delayed VEPs. Secondly, we found that pharmacological treatment, at best, only partially normalized EEG phenotypes. CTEP restored alpha/beta-band coherence and AEP amplitudes but failed to normalize gamma power and VEP latencies. Conversely, arbaclofen reduced gamma power but did not restore coherence or AEP amplitudes and further delayed VEPs. Gaboxadol did not normalize any EEG phenotypes. We conclude that these compounds have limited ability to normalize these EEG phenotypes.

Gut microbial 'TNFα-sphingolipids-steroid hormones' axis in children with autism spectrum disorder: an insight from meta-omics analysis

BACKGROUND

Autism spectrum disorder (ASD) is a persistent neurodevelopmental disorder affecting brains of children. Mounting evidences support the associations between gut microbial dysbiosis and ASD, whereas detailed mechanisms are still obscure.

METHODS

Here we probed the potential roles of gut microbiome in ASD using fecal metagenomics and metabolomics.

RESULTS

Children with ASD were found to be associated with augmented serum cytokines milieu, especially TNFα. Metagenomic analysis generated 29 differential species and 18 dysregulated functional pathways such as Bifidobacterium bifidum, Segatella copri, and upregulated 'Sphingolipid metabolism' in children with ASD. Metabolomics revealed steroid hormone dysgenesis in children with ASD with lower abundances of metabolites such as estriol, estradiol and deoxycorticosterone. A three-way association analysis showed positive correlations between TNFα and microbial function potentials such as 'Bacterial toxins' and 'Lysosome', indicating the contribution of microbial dysbiosis to neuroinflammation. TNFα also correlated positively with 'Sphingolipid metabolism', which further showed negative correlations with metabolites estriol and deoxycorticosterone. Such results, in consistent with current findings, revealed the contribution of increased TNFα to upregulated sphingolipid metabolism, which further impaired steroid hormone biosynthesis.

CONCLUSION

Our study proposed the gut microbial 'TNFα-sphingolipids-steroid hormones' axis in children with ASD, which may provide new perspectives for developing gut microbiome-based treatments in the future.

Calcium Signalling in Neurological Disorders, with Insights from Miniature Fluorescence Microscopy

Neurological disorders (NDs), such as amyotrophic lateral sclerosis (ALS), Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD), and schizophrenia, represent a complex and multifaceted health challenge that affects millions of people around the world. Growing evidence suggests that disrupted neuronal calcium signalling contributes to the pathophysiology of NDs. Additionally, calcium functions as a ubiquitous second messenger involved in diverse cellular processes, from synaptic activity to intercellular communication, making it a potential therapeutic target. Recently, the development of the miniature fluorescence microscope (miniscope) enabled simultaneous recording of the spatiotemporal calcium activity from large neuronal ensembles in unrestrained animals, providing a novel method for studying NDs. In this review, we discuss the abnormalities observed in calcium signalling and its potential as a therapeutic target for NDs. Additionally, we highlight recent studies that utilise miniscope technology to investigate the alterations in calcium dynamics associated with NDs.

Results from a Double-Blind, Randomized, Placebo-Controlled, Single-Dose, Crossover Trial of Lovastatin or Minocycline in Fragile X Syndrome

Introduction: Treatment studies in FMR1 knockout rodent models have found that minocycline and lovastatin each improve synaptic, neurological, and behavioral functioning, and open-label chronic dosing studies in human patients with fragile X syndrome (FXS) have demonstrated modest clinical improvements. Findings from blinded studies are mixed, and there is a limited understanding of electrophysiological target engagement that would facilitate cross-species translational studies. Smaller-scale, acute (e.g., single-dose) drug studies may speed treatment identification by detecting subtle electrophysiological and behavioral changes. Materials and Methods: Twenty-nine participants with FXS (31% female) ages 15-45 years completed a randomized, double-blind, crossover study in which they received a single oral dose of 40 mg of lovastatin, 270 mg of minocycline, or placebo, with a 2-week washout period between dosing visits. Participants completed a comprehensive neuropsychological battery and three EEG paradigms (resting state; auditory chirp; auditory habituation) before and 4 hours after dosing. Results: No serious adverse events were reported, and both drugs were well-tolerated. Compared with placebo, there were no overall treatment effects for any outcomes, including EEG, but several modest drug responses varied as a function of sex and age. Lovastatin treatment was associated with improved spatial awareness in older participants and females compared with minocycline and placebo. Discussion: We show that single-dose drug studies are highly feasible in FXS and that patients with FXS can complete a range of EEG and behavioral tasks, many of which have been shown to be reliable and may therefore be sensitive to subtle drug target engagement. Conclusions: Acute single doses of lovastatin or minocycline did not lead to changes in electrophysiological or performance-based measures. This may be due to the limited effects of these drugs in human patients or limited acute effects relative to chronic dosing. However, the study design was further validated for use in neurodevelopmental populations.

Drug Treatments for Neurodevelopmental Disorders: Targeting Signaling Pathways and Homeostasis

PURPOSE OF THE REVIEW

Preclinical and clinical evidence support the notion that neurodevelopmental disorders (NDDs) are synaptic disorders, characterized by excitatory-inhibitory imbalance. Despite this, NDD drug development programs targeting glutamate or gamma-aminobutyric acid (GABA) receptors have been largely unsuccessful. Nonetheless, recent drug trials in Rett syndrome (RTT), fragile X syndrome (FXS), and other NDDs targeting other mechanisms have met their endpoints. The purpose of this review is to identify the basis of these successful studies.

RECENT FINDINGS

Despite increasing evidence of disruption in synaptic homeostasis, most genetic variants associated with NDDs implicate proteins involved in cell regulation and not in neurotransmission. Metabolic processes, in particular mitochondrial function, appear to play a role in NDD pathophysiology. NDDs are also characterized by distinctive cell signaling abnormalities, which link cellular and synaptic homeostasis. Recent successful trials in NDDs, including those of trofinetide, the first drug specifically approved for one of these disorders (i.e., RTT), implicate the targeting of downstream processes (i.e., signaling pathways) rather than neurotransmitter receptors. Recent positive drug studies in NDDs and their underlying mechanisms, in conjunction with new knowledge on the pathophysiology of these disorders, support the concept that targeting signaling and cellular and synaptic homeostasis may be a preferred approach for ameliorating synaptic abnormalities in many NDDs.

Ascorbic Acid Ameliorates Molecular and Developmental Defects in Human-Induced Pluripotent Stem Cell and Cerebral Organoid Models of Fragile X Syndrome

Fragile X Syndrome (FX) is the most common form of inherited cognitive impairment and falls under the broader category of Autism Spectrum Disorders (ASD). FX is caused by a CGG trinucleotide repeat expansion in the non-coding region of the X-linked Fragile X Messenger Ribonucleoprotein 1 (FMR1) gene, leading to its hypermethylation and epigenetic silencing. Animal models of FX rely on the deletion of the Fmr1 gene, which fails to replicate the epigenetic silencing mechanism of the FMR1 gene observed in human patients. Human stem cells carrying FX repeat expansions have provided a better understanding of the basis of epigenetic silencing of FMR1. Previous studies have found that 5-Azacytidine (5Azac) can reverse this methylation; however, 5Azac can be toxic, which may limit its therapeutic potential. Here, we show that the dietary factor Ascorbic Acid (AsA) can reduce DNA methylation in the FMR1 locus and lead to an increase in FMR1 gene expression in FX iPSCs and cerebral organoids. In addition, AsA treatment rescued neuronal gene expression and morphological defects observed in FX iPSC-derived cerebral organoids. Hence, we demonstrate that the dietary co-factor AsA can partially revert the molecular and morphological defects seen in human FX models in vitro. Our findings have implications for the development of novel therapies for FX in the future.

Neurophysiological effects of a combined treatment of lovastatin and minocycline in patients with fragile X syndrome: Ancillary results of the LOVAMIX randomized clinical trial

Fragile X syndrome (FXS) is the primary hereditary cause of intellectual disability and autism spectrum disorder. It is characterized by exacerbated neuronal excitability, and its correction is considered an objective measure of treatment response in animal models, a marker albeit rarely used in clinical trials. Here, we used an extensive transcranial magnetic stimulation (TMS) battery to assess the neurophysiological effects of a therapy combining two disease-modifying drugs, lovastatin (40 mg) and minocycline (100 mg), administered alone for 8 weeks and in combination for 12 weeks, in 19 patients (mean age of 23.58 ± 1.51) with FXS taking part in the LOVAmix trial. The TMS battery, which included the resting motor threshold, short-interval intracortical inhibition, long-interval intracortical inhibition, corticospinal silent period, and intracortical facilitation, was completed at baseline after 8 weeks of monotherapy (visit 2 of the clinical trial) and after 12 weeks of dual therapy (visit 4 of the clinical trial). Repeated measure ANOVAs were performed between baseline and visit 2 (monotherapy) and visit 3 (dual therapy) with interactions for which monotherapy the participants received when they began the clinical trial. Results showed that dual therapy was associated with reduced cortical excitability after 20 weeks. This was reflected by a significant increase in the resting-motor threshold after dual therapy compared to baseline. There was a tendency for enhanced short-intracortical inhibition, a marker of GABAa-mediated inhibition after 8 weeks of monotherapy compared to baseline. Together, these results suggest that a combined therapy of minocycline and lovastatin might act on the core neurophysiopathology of FXS. This trial was registered at clinicaltrials.gov (NCT02680379).

Oligodendroglia and myelin pathology in fragile X syndrome

Studies of the pathophysiology of fragile X syndrome (FXS) have predominantly focused on synaptic and neuronal disruptions in the disease. However, emerging studies highlight the consistency of white matter abnormalities in the disorder. Recent investigations using animal models of FXS have suggested a role for the fragile X translational regulator 1 protein (FMRP) in the development and function of oligodendrocytes, the myelinating cells of the central nervous system. These studies are starting to uncover FMRP's involvement in the regulation of myelin-related genes, such as myelin basic protein, and its influence on the maturation and functionality of oligodendrocyte precursor cells and oligodendrocytes. Here, we consider evidence of white matter abnormalities in FXS, review our current understanding of FMRP's role in oligodendrocyte development and function, and highlight gaps in our knowledge of the pathogenic mechanisms that may contribute to white matter abnormalities in FXS. Addressing these gaps may help identify new therapeutic strategies aimed at enhancing outcomes for individuals affected by FXS.

Nanoplatform-Based In Vivo Gene Delivery Systems for Cancer Therapy

Gene therapy uses modern molecular biology methods to repair disease-causing genes. As a burgeoning therapeutic, it has been widely applied for cancer therapy. Since 1989, there have been numerous clinical gene therapy cases worldwide. However, a few are successful. The main challenge of clinical gene therapy is the lack of efficient and safe vectors. Although viral vectors show high transfection efficiency, their application is still limited by immune rejection and packaging capacity. Therefore, the development of non-viral vectors is overwhelming. Nanoplatform-based non-viral vectors become a hotspot in gene therapy. The reasons are mainly as follows. 1) Non-viral vectors can be engineered to be uptaken by specific types of cells or tissues, providing effective targeting capability. 2) Non-viral vectors can protect goods that need to be delivered from degradation. 3) Nanoparticles can transport large-sized cargo such as CRISPR/Cas9 plasmids and nucleoprotein complexes. 4) Nanoparticles are highly biosafe, and they are not mutagenic in themselves compared to viral vectors. 5) Nanoparticles are easy to scale preparation, which is conducive to clinical conversion and application. Here, an overview of the categories of nanoplatform-based non-viral gene vectors, the limitations on their development, and their applications in cancer therapy.

Phenotypic analysis of multielectrode array EEG biomarkers in developing and adult male Fmr1 KO mice

Fragile X Syndrome (FXS) is a leading known genetic cause of intellectual disability with symptoms that include increased anxiety and social and sensory processing deficits. Recent electroencephalographic (EEG) studies in humans with FXS have identified neural oscillation deficits that include increased resting state gamma power, increased amplitude of auditory evoked potentials, and reduced phase locking of sound-evoked gamma oscillations. Similar EEG phenotypes are present in mouse models of FXS, but very little is known about the development of such abnormal responses. In the current study, we employed a 30-channel mouse multielectrode array (MEA) system to record and analyze resting and stimulus-evoked EEG signals in male P21 and P91 WT and Fmr1 KO mice. This led to several novel findings. First, P91, but not P21, Fmr1 KO mice have significantly increased resting EEG power in the low- and high-gamma frequency bands. Second, both P21 and P91 Fmr1 KO mice have markedly attenuated inter-trial phase coherence (ITPC) to spectrotemporally dynamic auditory stimuli as well as to 40 Hz and 80 Hz auditory steady-state response (ASSR) stimuli. This suggests abnormal temporal processing from early development that may lead to abnormal speech and language function in FXS. Third, we found hemispheric asymmetry of fast temporal processing in the mouse auditory cortex in WT but not Fmr1 KO mice. Together, these findings define a set of EEG phenotypes in young and adult mice that can serve as translational targets for genetic and pharmacological manipulation in phenotypic rescue studies.

Clinical Characteristics, Developmental Trajectory, and Caregiver Burden of Patients With Creatine Transporter Deficiency (SLC6A8)

BACKGROUND AND OBJECTIVES

Creatine transporter deficiency (CTD) is a rare X-linked genetic disorder characterized by intellectual disability (ID). We evaluated the clinical characteristics and trajectory of patients with CTD and the impact of the disease on caregivers to identify relevant endpoints for future therapeutic trials.

METHODS

As part of a French National Research Program, patients with CTD were included based on (1) a pathogenic SLC6A8 variant and (2) ID and/or autism spectrum disorder. Families and patients were referred by the physician who ordered the genetic analysis through Reference Centers of ID from rare causes and inherited metabolic diseases. After we informed the patients and their parents/guardians about the study, all of them gave written consent and were included. A control group of age-matched and sex-matched patients with Fragile X syndrome was also included. Physical examination, neuropsychological assessments, and caregiver impact were assessed. All data were analyzed using R software.

RESULTS

Thirty-one patients (27 male, 4 female) were included (25/31 aged 18 years or younger). Most of the patients (71%) had symptoms at <24 months of age. The mean age at diagnosis was 6.5 years. Epilepsy occurred in 45% (mean age at onset: 8 years). Early-onset behavioral disorder occurred in 82%. Developmental trajectory was consistently delayed (fine and gross motor skills, language, and communication/sociability). Half of the patients with CTD had axial hypotonia during the first year of life. All patients were able to walk without help, but 7/31 had ataxia and only 14/31 could walk tandem gait. Most of them had abnormal fine motor skills (27/31), and most of them had language impairment (30/31), but 12/23 male patients (52.2%) completed the Peabody Picture Vocabulary Test. Approximately half (14/31) had slender build. Most of them needed nursing care (20/31), generally 1-4 h/d. Adaptive assessment (Vineland) confirmed that male patients with CTD had moderate-to-severe ID. Most caregivers (79%) were at risk of burnout, as shown by Caregiver Burden Inventory (CBI) > 36 (significantly higher than for patients with Fragile X syndrome) with a high burden of time dependence.

DISCUSSION

In addition to clinical endpoints, such as the assessment of epilepsy and the developmental trajectory of the patient, the Vineland scale, PPVT5, and CBI are of particular interest as outcome measures for future trials.

TRIAL REGISTRATION INFORMATION

ANSM Registration Number 2010-A00327-32.

Tackling myelin deficits in neurodevelopmental disorders using drug delivery systems

Interest in myelin and its roles in almost all brain functions has been greatly increasing in recent years, leading to countless new studies on myelination, as a dominant process in the development of cognitive functions. Here, we explore the unique role myelin plays in the central nervous system and specifically discuss the results of altered myelination in neurodevelopmental disorders. We present parallel developmental trajectories involving myelination that correlate with the onset of cognitive impairment in neurodevelopmental disorders and discuss the key challenges in the treatment of these chronic disorders. Recent developments in drug repurposing and nano/micro particle-based therapies are reviewed as a possible pathway to circumvent some of the main hurdles associated with early intervention, including patient's adherence and compliance, side effects, relapse, and faster route to possible treatment of these disorders. The strategy of drug encapsulation overcomes drug solubility and metabolism, with the possibility of drug targeting to a specific compartment, reducing side effects upon systemic administration.

Challenges in developing therapies in fragile X syndrome: how the FXLEARN trial can guide research

Fragile X syndrome (FXS), the most common inherited cause of intellectual disability and the single-gene cause of autism, is caused by decreased expression of the fragile X messenger ribonucleoprotein protein (FMRP), a ribosomal-associated RNA-binding protein involved in translational repression. Extensive preclinical work in several FXS animal models supported the therapeutic potential of decreasing metabotropic glutamate receptor (mGluR) signaling to correct translation of proteins related to synaptic plasticity; however, multiple clinical trials failed to show conclusive evidence of efficacy. In this issue of the JCI, Berry-Kravis and colleagues conducted the FXLEARN clinical trial to address experimental design concerns from previous trials. Unfortunately, despite treatment of young children with combined pharmacological and learning interventions for a prolonged period, no efficacy of blocking mGluR activity was observed. Future systematic evaluation of potential therapeutic approaches should evaluate consistency between human and animal pathophysiological mechanisms, utilize innovative clinical trial design from FXLEARN, and incorporate translatable biomarkers.

Intermittent Hypobaric Hypoxia Ameliorates Autistic-Like Phenotypes in Mice

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by persistent deficits in social communication and stereotyped behaviors. Although major advances in basic research on autism have been achieved in the past decade, and behavioral interventions can mitigate the difficulties that individuals with autism experience, little is known about the many fundamental issues of the interventions, and no specific medication has demonstrated efficiency for the core symptoms of ASD. Intermittent hypobaric hypoxia (IHH) is characterized by repeated exposure to lowered atmospheric pressure and oxygen levels, which triggers multiple physiological adaptations in the body. Here, using two mouse models of ASD, male Shank3B -/- and Fmr1 -/y mice, we found that IHH training at an altitude of 5,000 m for 4 h per day, for 14 consecutive days, ameliorated autistic-like behaviors. Moreover, IHH training enhanced hypoxia inducible factor (HIF) 1α in the dorsal raphe nucleus (DRN) and activated the DRN serotonergic neurons. Infusion of cobalt chloride into the DRN, to mimic IHH in increasing HIF1α expression or genetically knockdown PHD2 to upregulate HIF1α expression in the DRN serotonergic neurons, alleviated autistic-like behaviors in Shank3B -/- mice. In contrast, downregulation of HIF1α in DRN serotonergic neurons induced compulsive behaviors. Furthermore, upregulating HIF1α in DRN serotonergic neurons increased the firing rates of these neurons, whereas downregulation of HIF1α in DRN serotonergic neurons decreased their firing rates. These findings suggest that IHH activated DRN serotonergic neurons via upregulation of HIF1α, and thus ameliorated autistic-like phenotypes, providing a novel therapeutic option for ASD.

Characterising the behaviours in most severe and least severe emotional outbursts in young people

Emotional outbursts are displays of intense, challenging behaviour and are prevalent in individuals with neurodevelopmental disorders. Outbursts present a danger to individuals and their carers and are cited as reasons for referral to mental health services. However, it is currently unclear how the characteristics of outbursts may determine their severity. Carers (n = 214) of individuals aged between 6 and 25 and experiencing outbursts at least once per month completed the Emotional Outburst Questionnaire. Questionnaire items were used to compare behaviours observed in most severe and least severe outbursts through quantitative and content analyses of open ended data. Signs of physiological arousal and aggression were seen significantly more in most severe outbursts compared to least severe outbursts. Least severe outbursts were seen more frequently, but most severe outbursts were reported to have a longer duration, be at a higher intensity, and have a longer recovery time. Additionally, associations were found between reduced eye contact and most severe outbursts, as well as expression of suicidal ideation and most severe outbursts. Certain behaviours, notably forms of aggression and physiological arousal, are associated with most severe outbursts. Findings of this study may allow future work examining cross-disorder differences in outbursts to inform targeted interventions aiming to reduce outburst severity and impact. Additionally, identification of such outburst characteristics could aid in measurement of outburst severity, which would allow for more reliable and valid studies on outburst interventions.

Latent Class Analysis Identifies Distinctive Behavioral Subtypes in Children with Fragile X Syndrome

Fragile X syndrome (FXS) is characterized by variable neurobehavioral abnormalities, which leads to difficulties in developing and evaluating treatments and in determining accurate prognosis. We employed a pediatric cross-sectional sample (1,072 males, 338 females) from FORWARD, a clinic-based natural history study, to identify behavioral subtypes by latent class analysis. Input included co-occurring behavioral conditions, sleep and sensory problems, autistic behavior scales (SCQ, SRS-2), and the Aberrant Behavior Checklist revised for FXS (ABCFX). A 5-class solution yielded the most clinically meaningful, pharmacotherapy independent behavioral groups with distinctive SCQ, SRS-2, and ABCFX profiles, and adequate non-overlap (≥ 71%): "Mild" (31%), "Moderate without Social Impairment" (32%), "Moderate with Social Impairment" (7%), "Moderate with Disruptive Behavior" (20%), and "Severe" (9%). Our findings support FXS subtyping, for improving clinical management and therapeutic development.

Caregiver-reported outcomes with real-world use of cannabidiol in Lennox-Gastaut syndrome and Dravet syndrome from the BECOME survey

PURPOSE

Plant-derived highly purified cannabidiol (CBD) reduced the frequency of seizures associated with Lennox-Gastaut syndrome (LGS) and Dravet syndrome (DS) and improved the overall condition of patients in placebo-controlled phase 3 clinical trials. Anecdotal reports also suggest a positive effect on nonseizure outcomes. In this study, we aimed to identify, through a caregiver survey which nonseizure outcomes were most likely to change in these patients.

METHODS

The BEhavior, COgnition, and More with Epidiolex® (BECOME) was a 20-minute, cross-sectional, online survey that was developed with extensive input from caregivers, healthcare professionals, and epilepsy researchers, and was based on questions from validated measures and previously published caregiver reports. US-based caregivers (from Jazz Pharmaceuticals patient/caregiver database) of people with LGS or DS who were treated with CBD (Epidiolex®, 100 mg/mL oral solution) for ≥3 months were asked to compare the past month to the period before CBD initiation and rate their impression of changes using symmetrical Likert scales.

RESULTS

A total of 498 caregivers (97% parents) of patients with LGS (80%) or DS (20%) completed the survey. Mean (range) age of patients was 16 (1-73) years, and 52% were male. Patients were taking a median CBD dose of 14 mg/kg/d and median 4 concomitant antiseizure medications. A large proportion of respondents reported improvements in ≥1 survey question for all nonseizure-related domains: alertness, cognition, and executive function (85%); emotional functioning (82%); language and communication (79% in nonverbal patients and 74% in verbal); activities of daily living (51%); sleep (51%); and physical functioning (46%). Respondents reported improvements in seizure-related domains, including overall seizure frequency (85%), overall seizure severity (76%), seizure-free days per week for ≥1 seizure type (67%), and seizure freedom during the past month (16%). The majority of respondents who reported reduction in seizure frequency also reported improvements in nonseizure outcomes domains (51-80%). However, improvements in nonseizure outcomes (18-56%) were also reported in patients who either had no change or worsening of seizure frequency.

CONCLUSIONS

This survey characterized and quantified caregiver impression of changes in the seizure and nonseizure outcomes in patients taking add-on CBD treatment. Overall, 93% of caregivers reported planning to continue CBD treatment, primarily because of reduced seizure burden but also because of improvements in nonseizure-related outcomes. Despite the limitations that are associated with a retrospective survey-based study design, these results support further evaluation of the effect of CBD treatment on nonseizure outcomes among patients with LGS or DS.

Pharmacological management of fragile X syndrome: a systematic review and narrative summary of the current evidence

INTRODUCTION

Fragile X syndrome (FXS) is the most common inherited cause of Intellectual Disability. There is a broad phenotype that includes deficits in cognition and behavioral changes, alongside physical characteristics. Phenotype depends upon the level of mutation in the FMR1 (fragile X messenger ribonucleoprotein 1) gene. The molecular understanding of the impact of the FMR1 gene mutation provides an opportunity to target treatment not only at symptoms but also on a molecular level.

METHODS

We conducted a systematic review to provide an up-to-date narrative summary of the current evidence for pharmacological treatment in FXS. The review was restricted to randomized, blinded, placebo-controlled trials.

RESULTS

The outcomes from these studies are discussed and the level of evidence assessed against validated criteria. The initial search identified 2377 articles, of which 16 were included in the final analysis.

CONCLUSION

Based on this review to date there is limited data to support any specific pharmacological treatments, although the data for cannabinoids are encouraging in those with FXS and in future developments in gene therapy may provide the answer to the search for precision medicine. Treatment must be person-centered and consider the combination of medical, genetic, cognitive, and emotional challenges.

A novel combination treatment for fragile X syndrome predicted using computational methods

Fragile X syndrome is a neurodevelopmental disorder caused by silencing of the fragile X messenger ribonucleotide gene. Patients display a wide spectrum of symptoms ranging from intellectual and learning disabilities to behavioural challenges including autism spectrum disorder. In addition to this, patients also display a diversity of symptoms due to mosaicism. These factors make fragile X syndrome a difficult syndrome to manage and suggest that a single targeted therapeutic approach cannot address all the symptoms. To this end, we utilized Healx's data-driven drug discovery platform to identify a treatment strategy to address the wide range of diverse symptoms among patients. Computational methods identified the combination of ibudilast and gaboxadol as a treatment for several pathophysiological targets that could potentially reverse multiple symptoms associated with fragile X syndrome. Ibudilast is an approved broad-spectrum phosphodiesterase inhibitor, selective against both phosphodiesterase 4 and phosphodiesterase 10, and has demonstrated to have several beneficial effects in the brain. Gaboxadol is a GABAA receptor agonist, selective against the delta subunit, which has previously displayed encouraging results in a fragile X syndrome clinical trial. Alterations in GABA and cyclic adenosine monophosphate metabolism have long since been associated with the pathophysiology of fragile X syndrome; however, targeting both pathways simultaneously has never been investigated. Both drugs have a good safety and tolerability profile in the clinic making them attractive candidates for repurposing. We set out to explore whether the combination of ibudilast and gaboxadol could demonstrate therapeutic efficacy in a fragile X syndrome mouse model. We found that daily treatment with ibudilast significantly enhanced the ability of fragile X syndrome mice to perform a number of different cognitive assays while gaboxadol treatment improved behaviours such as hyperactivity, aggression, stereotypy and anxiety. Importantly, when ibudilast and gaboxadol were co-administered, the cognitive deficits as well as the aforementioned behaviours were rescued. Moreover, this combination treatment showed no evidence of tolerance, and no adverse effects were reported following chronic dosing. This work demonstrates for the first time that by targeting multiple pathways, with a combination treatment, we were able to rescue more phenotypes in a fragile X syndrome mouse model than either ibudilast or gaboxadol could achieve as monotherapies. This combination treatment approach holds promise for addressing the wide spectrum of diverse symptoms in this heterogeneous patient population and may have therapeutic potential for idiopathic autism.

EEG Biomarkers for Autism: Rational, Support, and the Qualification Process

In this chapter, we highlight the advantages, progress, and pending challenges of developing electroencephalography (EEG) and event-related potential (ERP) biomarkers for use in autism spectrum disorder (ASD). We describe reasons why global efforts towards precision treatment in ASD are utilizing EEG indices to quantify biological mechanisms. We overview common sensory processing and attention biomarkers and provide translational examples examining the genetic etiology of autism across animal models and human subgroups. We describe human-specific social biomarkers related to face perception, a complex social cognitive process that may prove informative of autistic social behaviors. Lastly, we discuss outstanding considerations for quantifying EEG biomarkers, the challenges associated with rigor and reproducibility, contexts of future use, and propose opportunities for combinatory multidimensional biomarkers.

Group I and group II metabotropic glutamate receptors are upregulated in the synapses of infant rats prenatally exposed to valproic acid

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental disorder characterized by impaired social interaction and restricted/stereotyped behavior. Prenatal exposure to valproic acid (VPA) is associated with an increased risk of developing ASD in humans and autistic-like behaviors in rodents. Increasing evidence indicates that dysfunctions of glutamate receptors at synapses are associated with ASD. In the VPA rat model, an involvement of glutamate receptors in autism-like phenotypes has been suggested; however, few studies were carried out on metabotropic glutamate (mGlu) receptors.

OBJECTIVES

We examined the protein expression levels of group I (mGlu1 and mGlu5) and group II (mGlu2/3) mGlu receptors in rats prenatally exposed to VPA and evaluated the effect of mGlu receptor modulation on an early autism-like phenotype in these animals.

METHODS

We used western blotting analysis on synaptosomes obtained from forebrain of control and VPA rats at different ages (postnatal day P13, 35, 90) and carried out ultrasonic vocalization (USV) emission test in infant control and VPA rats.

RESULTS

The expression levels of all these receptors were significantly increased in infant VPA rats. No changes were detected in adolescent and adult rats. An acute treatment with the preferential mGlu2/3 antagonist, LY341495, attenuated the impairment in the USV emission in VPA rats. No effect was observed after a treatment with the mGlu5 selective antagonist, MTEP.

CONCLUSIONS

Our findings demonstrate that the expression of group I and group II mGlu receptors is upregulated at synapses of infant VPA rats and suggest that mGlu2/3 receptor modulation may have a therapeutic potential in ASD.

Restoring prefrontal cortical excitation-inhibition balance with cannabidiol ameliorates neurobehavioral abnormalities in a mouse model of neurodevelopmental disorders

Maternal immune activation (MIA) resulting from viral infections during pregnancy is linked to increased rates of neurodevelopmental disorders in offspring. However, the mechanisms underlying MIA-induced neurobehavioral abnormalities remain unclear. Here, we used a poly (I:C)-induced MIA mouse model to demonstrate the presence of multiple behavioral deficits in male offspring. Through RNA sequencing (RNA-seq), we identified significant upregulation of genes involved in axonogenesis, synaptogenesis, and glutamatergic synaptic neurotransmission in the mPFC of MIA mice. Electrophysiological analyses further revealed an excitatory-inhibitory (E/I) synaptic imbalance in mPFC pyramidal neurons, leading to hyperactivity in this brain region. Cannabidiol (CBD) effectively alleviated the behavioral abnormalities observed in MIA offspring by reducing glutamatergic transmission and enhancing GABAergic neurotransmission of mPFC pyramidal neurons. Activation of GPR55 by lipid lysophosphatidylinositol (LPI), an endogenous GPR55 agonist, specifically in the mPFC of healthy animals led to MIA-associated behavioral phenotypes, which CBD could effectively reverse. Moreover, we found that a GPR55 antagonist can mimic CBD's beneficial effects, indicating that CBD's therapeutic effects are mediated via the LPI-GPR55 signaling pathway. Therefore, we identified mPFC as a primary node of a neural network that mediates MIA-induced behavioral abnormalities in offspring. Our work provides insights into the mechanisms underlying the developmental consequences of MIA and identifies CBD as a promising therapeutic approach to alleviate these effects.

Hyperexcitability in the Olfactory Bulb and Impaired Fine Odor Discrimination in the Fmr1 KO Mouse Model of Fragile X Syndrome

Fragile X syndrome (FXS) is the single most common monogenetic cause of autism spectrum disorders (ASDs) in humans. FXS is caused by loss of expression of the fragile X mental retardation protein (FMRP), an mRNA-binding protein encoded on the X chromosome involved in suppressing protein translation. Sensory processing deficits have been a major focus of studies of FXS in both humans and rodent models of FXS, but olfactory deficits remain poorly understood. Here, we conducted experiments in wild-type (WT) and Fmr1 knock-out (KO; Fmr1-/y ) mice (males) that lack expression of the gene encoding FMRP to assess olfactory circuit and behavioral abnormalities. In patch-clamp recordings conducted in slices of the olfactory bulb, output mitral cells (MCs) in Fmr1 KO mice displayed greatly enhanced excitation under baseline conditions, as evidenced by a much higher rate of occurrence of spontaneous network-level events known as long-lasting depolarizations (LLDs). The higher probability of spontaneous LLDs (sLLDs), which appeared to be because of a decrease in GABAergic synaptic inhibition in glomeruli leading to more feedforward excitation, caused a reduction in the reliability of stimulation-evoked responses in MCs. In addition, in a go/no-go operant discrimination paradigm, we found that Fmr1 KO mice displayed impaired discrimination of odors in difficult tasks that involved odor mixtures but not altered discrimination of monomolecular odors. We suggest that the Fmr1 KO-induced reduction in MC response reliability is one plausible mechanism for the impaired fine odor discrimination.SIGNIFICANCE STATEMENT Fragile X syndrome (FXS) in humans is associated with a range of debilitating deficits including aberrant sensory processing. One sensory system that has received comparatively little attention in studies in animal models of FXS is olfaction. Here, we report the first comprehensive physiological analysis of circuit defects in the olfactory bulb in the commonly-used Fmr1 knock-out (KO) mouse model of FXS. Our studies indicate that Fmr1 KO alters the local excitation/inhibition balance in the bulb, similar to what Fmr1 KO does in other brain circuits, but through a novel mechanism that involves enhanced feedforward excitation. Furthermore, Fmr1 KO mice display behavioral impairments in fine odor discrimination, an effect that may be explained by changes in neural response reliability.

Ultrasonic vocalization phenotypes in the Ts65Dn and Dp(16)1Yey mouse models of Down syndrome

Down syndrome (DS) is a developmental disorder associated with a high incidence of challenges in vocal communication. DS can involve medical co-morbidities and structural social factors that may impact communication outcomes, which can present difficulties for the study of vocal communication challenges. Mouse models of DS may be used to study vocal communication differences associated with this syndrome and allow for greater control and consistency of environmental factors. Prior work has demonstrated differences in ultrasonic vocalization (USV) of the Ts65Dn mouse model of DS at a young adult age, however it is not known how USV characteristics are manifested at mature ages. Given that the aging process and age-related co-morbidities may also impact communication in DS, addressing this gap in knowledge may be of value for efforts to understand communication difficulties in DS across the lifespan. The current study hypothesized that the Ts65Dn and Dp(16)1Yey mouse models of DS would demonstrate differences in multiple measures of USV communication at a mature adult age of 5 months.

METHODS

Ts65Dn mice (n = 16) and euploid controls (n = 19), as well as Dp(16)1Yey mice (n = 20) and wild-type controls (n = 22), were evaluated at 5 months of age for USV production using a mating paradigm. Video footage of USV sessions were analyzed to quantify social behaviors of male mice during USV testing sessions. USV recordings were analyzed using Deepsqueak software to identify 10 vocalization types, which were quantified for 11 acoustic measures.

RESULTS

Ts65Dn, but not Dp(16)1Yey, showed significantly lower proportions of USVs classified as Step Up, Short, and Frequency Steps, and significantly higher proportions of USVs classified as Inverted U, than euploid controls. Both Ts65Dn and Dp(16)1Yey groups had significantly greater values for power and tonality for USVs than respective control groups. While Ts65Dn showed lower frequencies than controls, Dp(16)1Yey showed higher frequencies than controls. Finally, Ts65Dn showed reductions in a measure of complexity for some call types. No significant differences between genotype groups were identified in analysis of behaviors during testing sessions.

CONCLUSION

While both Ts65Dn and Dp(16)1Yey show significant differences in USV measures at 5 months of age, of the two models, Ts65Dn shows a relatively greater numbers of differences. Characterization of communication phenotypes in mouse models of DS may be helpful in laying the foundation for future translational advances in the area of communication difficulties associated with DS.

iBehavior-a preliminary proof of concept study of a smartphone-based tool for the assessment of behavior change in neurodevelopmental disabilities

Purpose

The purpose of the present study was to describe the content and function of iBehavior, a smartphone-based caregiver-report electronic ecological momentary assessment (eEMA) tool developed to assess and track behavior change in people with intellectual and developmental disabilities (IDDs), and to examine its preliminary validity.

Methods

Ten parents of children (ages of 5-17 years) with IDDs (n = 7 with fragile X syndrome; n = 3 with Down syndrome) rated their child's behavior (aggression and irritability, avoidant and fearful behavior, restricted and repetitive behavior and interests, and social initiation) using iBehavior once daily for 14 days. At the conclusion of the 14-day observation period, parents completed traditional rating scales as validation measures, as well as a user feedback survey.

Results

Across the 140 possible observations, 8 were skipped, leading to a 94% response rate over 10 participants' observation periods. Participants also completed 100% of items for each of their logged observations. Parent ratings using iBehavior showed emerging evidence of convergent validity among domains with traditional rating scales including the Behavior Rating Inventory of Executive Function 2 (BRIEF-2), and Aberrant Behavior Checklist-Community (ABC-C). iBehavior was feasible in the sample, and parent feedback indicated high overall satisfaction.

Conclusion

Results of the present pilot study indicate successful implementation and preliminary feasibility and validity of an eEMA tool for use as a behavioral outcome measure in IDDs.

The Psychedelic N,N-Dipropyltryptamine Prevents Seizures in a Mouse Model of Fragile X Syndrome via a Mechanism that Appears Independent of Serotonin and Sigma1 Receptors

The serotonergic psychedelic psilocybin shows efficacy in treating neuropsychiatric disorders, though the mechanism(s) underlying its therapeutic effects remain unclear. We show that a similar psychedelic tryptamine, N,N-dipropyltryptamine (DPT), completely prevents audiogenic seizures (AGS) in an Fmr1 knockout mouse model of fragile X syndrome at a 10 mg/kg dose but not at lower doses (3 or 5.6 mg/kg). Despite showing in vitro that DPT is a serotonin 5-HT2A, 5-HT1B, and 5-HT1A receptor agonist (with that rank order of functional potency, determined with TRUPATH Gα/βγ biosensors), pretreatment with selective inhibitors of 5-HT2A/2C, 5-HT1B, or 5-HT1A receptors did not block DPT's antiepileptic effects; a pan-serotonin receptor antagonist was also ineffective. Because 5-HT1A receptor activation blocks AGS in Fmr1 knockout mice, we performed a dose-response experiment to evaluate DPT's engagement of 5-HT1A receptors in vivo. DPT elicited 5-HT1A-dependent effects only at doses greater than 10 mg/kg, further supporting that DPT's antiepileptic effects were not 5-HT1A-mediated. We also observed that the selective sigma1 receptor antagonist, NE-100, did not impact DPT's antiepileptic effects, suggesting DPT engagement of sigma1 receptors was not a crucial mechanism. Separately, we observed that DPT and NE-100 at high doses caused convulsions on their own that were qualitatively distinct from AGS. In conclusion, DPT dose-dependently blocked AGS in Fmr1 knockout mice, but neither serotonin nor sigma1 receptor antagonists prevented this action. Thus, DPT might have neurotherapeutic effects independent of its serotonergic psychedelic properties. However, DPT also caused seizures at high doses, showing that DPT has complex dose-dependent in vivo polypharmacology.

Modeling SHANK3-associated autism spectrum disorder in Beagle dogs via CRISPR/Cas9 gene editing

Despite intensive studies in modeling neuropsychiatric disorders especially autism spectrum disorder (ASD) in animals, many challenges remain. Genetic mutant mice have contributed substantially to the current understanding of the molecular and neural circuit mechanisms underlying ASD. However, the translational value of ASD mouse models in preclinical studies is limited to certain aspects of the disease due to the apparent differences in brain and behavior between rodents and humans. Non-human primates have been used to model ASD in recent years. However, a low reproduction rate due to a long reproductive cycle and a single birth per pregnancy, and an extremely high cost prohibit a wide use of them in preclinical studies. Canine model is an appealing alternative because of its complex and effective dog-human social interactions. In contrast to non-human primates, dog has comparable drug metabolism as humans and a high reproduction rate. In this study, we aimed to model ASD in experimental dogs by manipulating the Shank3 gene as SHANK3 mutations are one of most replicated genetic defects identified from ASD patients. Using CRISPR/Cas9 gene editing, we successfully generated and characterized multiple lines of Beagle Shank3 (bShank3) mutants that have been propagated for a few generations. We developed and validated a battery of behavioral assays that can be used in controlled experimental setting for mutant dogs. bShank3 mutants exhibited distinct and robust social behavior deficits including social withdrawal and reduced social interactions with humans, and heightened anxiety in different experimental settings (n = 27 for wild-type controls and n = 44 for mutants). We demonstrate the feasibility of producing a large number of mutant animals in a reasonable time frame. The robust and unique behavioral findings support the validity and value of a canine model to investigate the pathophysiology and develop treatments for ASD and potentially other psychiatric disorders.

Effects of AFQ056 on language learning in fragile X syndrome

BACKGROUNDFXLEARN, the first-ever large multisite trial of effects of disease-targeted pharmacotherapy on learning, was designed to explore a paradigm for measuring effects of mechanism-targeted treatment in fragile X syndrome (FXS). In FXLEARN, the effects of metabotropic glutamate receptor type 5 (mGluR5) negative allosteric modulator (NAM) AFQ056 on language learning were evaluated in 3- to 6-year-old children with FXS, expected to have more learning plasticity than adults, for whom prior trials of mGluR5 NAMs have failed.METHODSAfter a 4-month single-blind placebo lead-in, participants were randomized 1:1 to AFQ056 or placebo, with 2 months of dose optimization to the maximum tolerated dose, then 6 months of treatment during which a language-learning intervention was implemented for both groups. The primary outcome was a centrally scored videotaped communication measure, the Weighted Communication Scale (WCS). Secondary outcomes were objective performance-based and parent-reported cognitive and language measures.RESULTSFXLEARN enrolled 110 participants, randomized 99, and had 91 who completed the placebo-controlled period. Although both groups made language progress and there were no safety issues, the change in WCS score during the placebo-controlled period was not significantly different between the AFQ056 and placebo-treated groups, nor were there any significant between-group differences in change in any secondary measures.CONCLUSIONDespite the large body of evidence supporting use of mGluR5 NAMs in animal models of FXS, this study suggests that this mechanism of action does not translate into benefit for the human FXS population and that better strategies are needed to determine which mechanisms will translate from preclinical models to humans in genetic neurodevelopmental disorders.TRIAL REGISTRATIONClincalTrials.gov NCT02920892.FUNDING SOURCESNeuroNEXT network NIH grants U01NS096767, U24NS107200, U24NS107209, U01NS077323, U24NS107183, U24NS107168, U24NS107128, U24NS107199, U24NS107198, U24NS107166, U10NS077368, U01NS077366, U24NS107205, U01NS077179, and U01NS077352; NIH grant P50HD103526; and Novartis IIT grant AFQ056X2201T for provision of AFQ056.

Neurodevelopment and early pharmacological interventions in Fragile X Syndrome

Fragile X Syndrome (FXS) is a neurodevelopmental disorder and the leading monogenic cause of autism and intellectual disability. For years, several efforts have been made to develop an effective therapeutic approach to phenotypically rescue patients from the disorder, with some even advancing to late phases of clinical trials. Unfortunately, none of these attempts have completely succeeded, bringing urgency to further expand and refocus research on FXS therapeutics. FXS arises at early stages of postnatal development due to the mutation and transcriptional silencing of the Fragile X Messenger Ribonucleoprotein 1 gene (FMR1) and consequent loss of the Fragile X Messenger Ribonucleoprotein (FMRP) expression. Importantly, FMRP expression is critical for the normal adult nervous system function, particularly during specific windows of embryogenic and early postnatal development. Cellular proliferation, migration, morphology, axonal guidance, synapse formation, and in general, neuronal network establishment and maturation are abnormally regulated in FXS, underlying the cognitive and behavioral phenotypes of the disorder. In this review, we highlight the relevance of therapeutically intervening during critical time points of development, such as early postnatal periods in infants and young children and discuss past and current clinical trials in FXS and their potential to specifically target those periods. We also discuss potential benefits, limitations, and disadvantages of these pharmacological tools based on preclinical and clinical research.

Blunted type-5 metabotropic glutamate receptor-mediated polyphosphoinositide hydrolysis in two mouse models of monogenic autism

The involvement of the mGlu5 receptors in the pathophysiology of several forms of monogenic autism has been supported by numerous studies following the seminal observation that mGlu5 receptor-dependent long-term depression was enhanced in the hippocampus of mice modeling the fragile-X syndrome (FXS). Surprisingly, there are no studies examining the canonical signal transduction pathway activated by mGlu5 receptors (i.e. polyphosphoinositide - PI - hydrolysis) in mouse models of autism. We have developed a method for in vivo assessment of PI hydrolysis based on systemic injection of lithium chloride followed by treatment with the selective mGlu5 receptor PAM, VU0360172, and measurement of endogenous inositolmonophosphate (InsP) in brain tissue. Here, we report that mGlu5 receptor-mediated PI hydrolysis was blunted in the cerebral cortex, hippocampus, and corpus striatum of Ube3a^m-/p+ mice modeling Angelman syndrome (AS), and in the cerebral cortex and hippocampus of fmr1 knockout mice modeling FXS. In vivo mGlu5 receptor-mediated stimulation of Akt on threonine 308 was also blunted in the hippocampus of FXS mice. These changes were associated with a significant increase in cortical and striatal Homer1 levels and striatal mGlu5 receptor and Gαq levels in AS mice, and with a reduction in cortical mGlu5 receptor and hippocampal Gαq levels, and an increase in cortical phospholipase-Cβ and hippocampal Homer1 levels in FXS mice. This is the first evidence that the canonical transduction pathway activated by mGlu5 receptors is down-regulated in brain regions of mice modeling monogenic autism.

Site-specific R-loops induce CGG repeat contraction and fragile X gene reactivation

Here, we describe an approach to correct the genetic defect in fragile X syndrome (FXS) via recruitment of endogenous repair mechanisms. A leading cause of autism spectrum disorders, FXS results from epigenetic silencing of FMR1 due to a congenital trinucleotide (CGG) repeat expansion. By investigating conditions favorable to FMR1 reactivation, we find MEK and BRAF inhibitors that induce a strong repeat contraction and full FMR1 reactivation in cellular models. We trace the mechanism to DNA demethylation and site-specific R-loops, which are necessary and sufficient for repeat contraction. A positive feedback cycle comprising demethylation, de novo FMR1 transcription, and R-loop formation results in the recruitment of endogenous DNA repair mechanisms that then drive excision of the long CGG repeat. Repeat contraction is specific to FMR1 and restores the production of FMRP protein. Our study therefore identifies a potential method of treating FXS in the future.

Updates on the Physiopathology of Group I Metabotropic Glutamate Receptors (mGluRI)-Dependent Long-Term Depression

Group I metabotropic glutamate receptors (mGluRI), including mGluR1 and mGluR5 subtypes, modulate essential brain functions by affecting neuronal excitability, intracellular calcium dynamics, protein synthesis, dendritic spine formation, and synaptic transmission and plasticity. Nowadays, it is well appreciated that the mGluRI-dependent long-term depression (LTD) of glutamatergic synaptic transmission (mGluRI-LTD) is a key mechanism by which mGluRI shapes connectivity in various cerebral circuitries, directing complex brain functions and behaviors, and that it is deranged in several neurological and psychiatric illnesses, including neurodevelopmental disorders, neurodegenerative diseases, and psychopathologies. Here, we will provide an updated overview of the physiopathology of mGluRI-LTD, by describing mechanisms of induction and regulation by endogenous mGluRI interactors, as well as functional physiological implications and pathological deviations.

Expressive language sampling and outcome measures for treatment trials in fragile X and down syndromes: composite scores and psychometric properties

The lack of psychometrically sound outcome measures has been a barrier to evaluating the efficacy of treatments proposed for core symptoms of intellectual disability (ID). Research on Expressive Language Sampling (ELS) procedures suggest it is a promising approach to measuring treatment efficacy. ELS entails collecting samples of a participant's talk in interactions with an examiner that are naturalistic but sufficiently structured to ensure consistency and limit examiner effects on the language produced. In this study, we extended previous research on ELS by analyzing an existing dataset to determine whether psychometrically adequate composite scores reflecting multiple dimensions of language can be derived from ELS procedures administered to 6- to 23-year-olds with fragile X syndrome (n = 80) or Down syndrome (n = 78). Data came from ELS conversation and narration procedures administered twice in a 4-week test-retest interval. We found that several composites emerged from variables indexing syntax, vocabulary, planning processes, speech articulation, and talkativeness, although there were some differences in the composites for the two syndromes. Evidence of strong test-retest reliability and construct validity of two of three composites were obtained for each syndrome. Situations in which the composite scores would be useful in evaluating treatment efficacy are outlined.

Trofinetide for the treatment of Rett syndrome: a randomized phase 3 study

Rett syndrome is a rare, genetic neurodevelopmental disorder. Trofinetide is a synthetic analog of glycine-proline-glutamate, the N-terminal tripeptide of the insulin-like growth factor 1 protein, and has demonstrated clinical benefit in phase 2 studies in Rett syndrome. In this phase 3 study ( https://clinicaltrials.gov identifier NCT04181723 ), females with Rett syndrome received twice-daily oral trofinetide (n = 93) or placebo (n = 94) for 12 weeks. For the coprimary efficacy endpoints, least squares mean (LSM) change from baseline to week 12 in the Rett Syndrome Behaviour Questionnaire for trofinetide versus placebo was -4.9 versus -1.7 (P = 0.0175; Cohen's d effect size, 0.37), and LSM Clinical Global Impression-Improvement at week 12 was 3.5 versus 3.8 (P = 0.0030; effect size, 0.47). For the key secondary efficacy endpoint, LSM change from baseline to week 12 in the Communication and Symbolic Behavior Scales Developmental Profile Infant-Toddler Checklist Social Composite score was -0.1 versus -1.1 (P = 0.0064; effect size, 0.43). Common treatment-emergent adverse events included diarrhea (80.6% for trofinetide versus 19.1% for placebo), which was mostly mild to moderate in severity. Significant improvement for trofinetide compared with placebo was observed for the coprimary efficacy endpoints, suggesting that trofinetide provides benefit in treating the core symptoms of Rett syndrome.

Electroencephalographic (EEG) Biomarkers in Genetic Neurodevelopmental Disorders

Collectively, neurodevelopmental disorders are highly prevalent, but more than a third of neurodevelopmental disorders have an identifiable genetic etiology, each of which is individually rare. The genes associated with neurodevelopmental disorders are often involved in early brain development, neuronal signaling, or synaptic plasticity. Novel treatments for many genetic neurodevelopmental disorders are being developed, but disease-relevant clinical outcome assessments and biomarkers are limited. Electroencephalography (EEG) is a promising noninvasive potential biomarker of brain function. It has been used extensively in epileptic disorders, but its application in neurodevelopmental disorders needs further investigation. In this review, we explore the use of EEG in 3 of the most prevalent genetic neurodevelopmental disorders-Angelman syndrome, Rett syndrome, and fragile X syndrome. Quantitative analyses of EEGs, such as power spectral analysis or measures of connectivity, can quantify EEG signatures seen on qualitative review and potentially correlate with phenotypes. In both Angelman syndrome and Rett syndrome, increased delta power on spectral analysis has correlated with clinical markers of disease severity including developmental disability and seizure burden, whereas spectral power analysis on EEG in fragile X syndrome tends to demonstrate abnormalities in gamma power. Further studies are needed to establish reliable relationships between quantitative EEG biomarkers and clinical phenotypes in rare genetic neurodevelopmental disorders.

iBehavior - A Smartphone-Based Ecological Momentary Assessment Tool for the Assessment of Behavior Change in Neurodevelopmental Disorders

The purpose of the present study was to describe the content and function of iBehavior, a smartphone-based caregiver-report electronic ecological momentary assessment (eEMA) tool developed to assess and track behavior change in people with intellectual and developmental disabilities (IDDs), and to examine its preliminary validity. Ten parents of children (ages of 5-17 years) with IDDs (n = 7 with fragile X syndrome; n = 3 with Down syndrome) rated their child's behavior (aggression and irritability, avoidant and fearful behavior, restricted and repetitive behavior and interests, and social initiation) using iBehavior once daily for 14 days. At the conclusion of the 14-day observation period, parents completed traditional rating scales as validation measures, as well as a user feedback survey. Parent ratings using iBehavior showed emerging evidence of convergent validity among domains with traditional rating scales including the Behavior Rating Inventory of Executive Function 2 (BRIEF-2), Aberrant Behavior Checklist - Community (ABC-C), and Conners 3. iBehavior was feasible in our sample, and parent feedback indicated high overall satisfaction. Results of the present pilot study indicate successful implementation and preliminary feasibility and validity of an eEMA tool for use as a behavioral outcome measure in IDDs.

Deregulation of ER-mitochondria contact formation and mitochondrial calcium homeostasis mediated by VDAC in fragile X syndrome

Loss of fragile X messenger ribonucleoprotein (FMRP) causes fragile X syndrome (FXS), the most prevalent form of inherited intellectual disability. Here, we show that FMRP interacts with the voltage-dependent anion channel (VDAC) to regulate the formation and function of endoplasmic reticulum (ER)-mitochondria contact sites (ERMCSs), structures that are critical for mitochondrial calcium (mito-Ca2+) homeostasis. FMRP-deficient cells feature excessive ERMCS formation and ER-to-mitochondria Ca2+ transfer. Genetic and pharmacological inhibition of VDAC or other ERMCS components restored synaptic structure, function, and plasticity and rescued locomotion and cognitive deficits of the Drosophila dFmr1 mutant. Expressing FMRP C-terminal domain (FMRP-C), which confers FMRP-VDAC interaction, rescued the ERMCS formation and mito-Ca2+ homeostasis defects in FXS patient iPSC-derived neurons and locomotion and cognitive deficits in Fmr1 knockout mice. These results identify altered ERMCS formation and mito-Ca2+ homeostasis as contributors to FXS and offer potential therapeutic targets.