The role of fragile X mental retardation protein in major mental disorders

An Update on Psychopharmacological Treatment of Autism Spectrum Disorder

While behavioral interventions remain the mainstay of treatment of autism spectrum disorder (ASD), several potential targeted treatments addressing the underlying neurophysiology of ASD have emerged in the last few years. These are promising for the potential to, in future, become part of the mainstay treatment in addressing the core symptoms of ASD. Although it is likely that the development of future targeted treatments will be influenced by the underlying heterogeneity in etiology, associated genetic mechanisms influencing ASD are likely to be the first targets of treatments and even gene therapy in the future for ASD. In this article, we provide a review of current psychopharmacological treatment in ASD including those used to address common comorbidities of the condition and upcoming new targeted approaches in autism management. Medications including metformin, arbaclofen, cannabidiol, oxytocin, bumetanide, lovastatin, trofinetide, and dietary supplements including sulforophane and N-acetylcysteine are discussed. Commonly used medications to address the comorbidities associated with ASD including atypical antipsychotics, serotoninergic agents, alpha-2 agonists, and stimulant medications are also reviewed. Targeted treatments in Fragile X syndrome (FXS), the most common genetic disorder leading to ASD, provide a model for new treatments that may be helpful for other forms of ASD. Appeared originally in Neurotherapeutics 2022; 19:248-262.

Variation of FMRP Expression in Peripheral Blood Mononuclear Cells from Individuals with Fragile X Syndrome

Fragile X syndrome (FXS) is the most common heritable cause of intellectual disability and autism spectrum disorder. The syndrome is often caused by greatly reduced or absent protein expression from the fragile X messenger ribonucleoprotein 1 (FMR1) gene due to expansion of a 5'-non-coding trinucleotide (CGG) element beyond 200 repeats (full mutation). To better understand the complex relationships among FMR1 allelotype, methylation status, mRNA expression, and FMR1 protein (FMRP) levels, FMRP was quantified in peripheral blood mononuclear cells for a large cohort of FXS (n = 154) and control (n = 139) individuals using time-resolved fluorescence resonance energy transfer. Considerable size and methylation mosaicism were observed among individuals with FXS, with FMRP detected only in the presence of such mosaicism. No sample with a minimum allele size greater than 273 CGG repeats had significant levels of FMRP. Additionally, an association was observed between FMR1 mRNA and FMRP levels in FXS samples, predominantly driven by those with the lowest FMRP values. This study underscores the complexity of FMR1 allelotypes and FMRP expression and prompts a reevaluation of FXS therapies aimed at reactivating large full mutation alleles that are likely not capable of producing sufficient FMRP to improve cognitive function.

Axonal and presynaptic FMRP: Localization, signal, and functional implications

Fragile X mental retardation protein (FMRP) binds a selected set of mRNAs and proteins to guide neural circuit assembly and regulate synaptic plasticity. Loss of FMRP is responsible for Fragile X syndrome, a neuropsychiatric disorder characterized with auditory processing problems and social difficulty. FMRP actions in synaptic formation, maturation, and plasticity are site-specific among the four compartments of a synapse: presynaptic and postsynaptic neurons, astrocytes, and extracellular matrix. This review summarizes advancements in understanding FMRP localization, signals, and functional roles in axons and presynaptic terminals.

Light in the Rational Treatment of Autism? Effects of Metformin on Steroid Hormones in a Patient with Polycystic Ovarian Syndrome (PCOS)

Background: Metformin is an effective treatment option for type 2 diabetes mellitus, and it is, to this day, the most prescribed oral antiglycaemic drug. Besides its effects mainly on mitochondrial activity, an off-label use came up as a pharmaceutical for subjects with a diagnosis of polycystic ovarian syndrome (PCOS) along with altered steroid hormone homeostasis. Besides these effects, even an influence on mood and social behavior was described, leading to the aim of this case report to elucidate the effects before versus after treatment with metformin on steroid hormones and social behavior. Methods: A female patient with diagnosed PCOS was analyzed three times for steroid hormone levels. The first analysis was performed before treatment; the second, after a period of 71 days with metformin at 2 × 500 mg; and the third, after a total of 144 days with metformin at 2 × 500 mg. Spot urine probes were taken in the morning for a combined gas chromatography−mass spectrometry (GC-MS), and the steroid levels were adjusted for creatinine excretion. A questionnaire on social behavior (Autism Spectrum Questionnaire) was administered before treatment and after 71 days. Results: A decrease in all the steroid hormones measured was detected after 71 and 144 days of treatment with metformin, being more pronounced after 144 days of treatment and highly significant (p < 0.001). Furthermore, in the untreated state, the class of corticosterone metabolites showed increased values compared to the female reference values for TH-11-DH-corticosterone, TH-corticosterone, and 5a-TH-corticosterone. In the class of estrogen metabolites, increased values compared to the reference values were detected for 17b-estradiol; in the class of 11-deoxycortisol metabolites, an increase in TH-11-deoxycortisol was detected. For the class of cortisol metabolites, increased values compared to the reference values were detected for cortisone, TH-cortisone, a-cortolone, b-cortolone, 20b-dihydrocortisone, cortisol, TH-cortisol, 5a-TH-cortisol, a-cortol, 20b-dihydrocortisol, and 6b-OH-cortisol. No increases in androgen metabolites were detected. Interestingly, weight decreased from 93.4 kg to 91.3 kg after 71 days and fell to 82.7 kg after 144 days of treatment. The skeletal muscle mass was 30.1 kg at the first visit, decreasing to 29.9 kg and to 27.5 kg. No significant difference in the social behavior score from baseline to after 71 days of treatment was detected. Discussion: Metformin improved the steroid hormone profiles from levels above the upper reference values to the middle of the reference values after 71 days and to the lower ends of the reference values after 144 days of treatment. This implies not only that metformin has an effect on steroid hormone levels, but in addition that the efficacy of the pharmaceutical seems to depend on the time interval from intake. To summarize, in this patient, steroid hormones were affected but social behavior was not. If no effect of metformin on social behavior exists, this must be supported by further cases.

Maternal Microbiota Modulate a Fragile X-like Syndrome in Offspring Mice

Maternal microbial dysbiosis has been implicated in adverse postnatal health conditions in offspring, such as obesity, cancer, and neurological disorders. We observed that the progeny of mice fed a Westernized diet (WD) with low fiber and extra fat exhibited higher frequencies of stereotypy, hyperactivity, cranial features and lower FMRP protein expression, similar to what is typically observed in Fragile X Syndrome (FXS) in humans. We hypothesized that gut dysbiosis and inflammation during pregnancy influenced the prenatal uterine environment, leading to abnormal phenotypes in offspring. We found that oral in utero supplementation with a beneficial anti-inflammatory probiotic microbe, Lactobacillus reuteri, was sufficient to inhibit FXS-like phenotypes in offspring mice. Cytokine profiles in the pregnant WD females showed that their circulating levels of pro-inflammatory cytokine interleukin (Il)-17 were increased relative to matched gravid mice and to those given supplementary L. reuteri probiotic. To test our hypothesis of prenatal contributions to this neurodevelopmental phenotype, we performed Caesarian (C-section) births using dissimilar foster mothers to eliminate effects of maternal microbiota transferred during vaginal delivery or nursing after birth. We found that foster-reared offspring still displayed a high frequency of these FXS-like features, indicating significant in utero contributions. In contrast, matched foster-reared progeny of L. reuteri-treated mothers did not exhibit the FXS-like typical features, supporting a key role for microbiota during pregnancy. Our findings suggest that diet-induced dysbiosis in the prenatal uterine environment is strongly associated with the incidence of this neurological phenotype in progeny but can be alleviated by addressing gut dysbiosis through probiotic supplementation.

Autism spectrum disorder in the fragile X premutation state: possible mechanisms and implications

There is increasing recognition of the heterogeneity of origin of cases of autism spectrum disorder (ASD) with multiple forms of ASD having been identified over the decades. Among these, a genetic etiology can be identified in 20-40% of cases when a full genetic work-up is completed. The Fragile X premutation state (characterized by the presence of 55-200 CGG repeats in the FMR1 gene) is a relatively newly identified disease state that has since been associated with several disorders including fragile X-associated tremor ataxia syndrome (FXTAS), fragile X-associated primary ovarian insufficiency (FXPOI) and most recently, fragile X-associated neurodevelopmental disorders (FXAND) which commonly includes anxiety and depression. In addition to these associated disorders, extant literature and clinical observations have suggested an association between the premutation state and ASD. In this paper, we review the literature pertinent to this and discuss possible molecular mechanisms that may explain this association. This includes lowered levels of the FMR1 Protein (FMRP), GABA deficits, mitochondrial dysfunction and secondary genetic abnormalities that is seen in premutation carriers as well as their increased vulnerability to environmental stressors. Understanding these mechanisms can facilitate development of targeted treatment for specific sub-groups of ASD and premutation disorders in future.

The Fragile X Protein Disordered Regions Bind a Novel RNA Target

The fragile X proteins (FXPs) are a family of RNA-binding proteins that regulate mRNA translation to promote proper neural development and cognition in mammals. Of particular interest to researchers is the fragile X mental retardation protein (FMRP), as its absence leads to a neurodevelopmental disorder: fragile X syndrome (FXS), the leading monogenetic cause of autism spectrum disorders. A primary focus of research has been to determine mRNA targets of the FXPs in vivo through pull-down techniques, and to validate them through in vitro binding studies; another approach has been to perform in vitro selection experiments to identify RNA sequence and structural targets. These mRNA targets can be further investigated as potential targets for FXS therapeutics. The most established RNA structural target of this family of proteins is the G-quadruplex. In this article, we report a 99 nucleotide RNA target that is bound by all three FXPs with nanomolar equilibrium constants. Furthermore, we determined that the last 102 amino acids of FMRP, which includes the RGG motif, were necessary and sufficient to bind this RNA target. To the best of our knowledge, this is one of only a few examples of non-G-quadruplex, non-homopolymer RNAs bound by the RGG motif/C-termini of FMRP.

An Update on Psychopharmacological Treatment of Autism Spectrum Disorder

While behavioral interventions remain the mainstay of treatment of autism spectrum disorder (ASD), several potential targeted treatments addressing the underlying neurophysiology of ASD have emerged in the last few years. These are promising for the potential to, in future, become part of the mainstay treatment in addressing the core symptoms of ASD. Although it is likely that the development of future targeted treatments will be influenced by the underlying heterogeneity in etiology, associated genetic mechanisms influencing ASD are likely to be the first targets of treatments and even gene therapy in the future for ASD. In this article, we provide a review of current psychopharmacological treatment in ASD including those used to address common comorbidities of the condition and upcoming new targeted approaches in autism management. Medications including metformin, arbaclofen, cannabidiol, oxytocin, bumetanide, lovastatin, trofinetide, and dietary supplements including sulforophane and N-acetylcysteine are discussed. Commonly used medications to address the comorbidities associated with ASD including atypical antipsychotics, serotoninergic agents, alpha-2 agonists, and stimulant medications are also reviewed. Targeted treatments in Fragile X syndrome (FXS), the most common genetic disorder leading to ASD, provide a model for new treatments that may be helpful for other forms of ASD.

Psychotropic Drug Treatment Patterns in Persons with Fragile X Syndrome

Objective: Psychiatric comorbidity is common in fragile X syndrome (FXS) and often addressed through pharmacological management. Here we examine data in the Fragile X Online Registry With Accessible Research Database (FORWARD) to characterize specific symptoms being treated with psychotropic medication, patterns of medication use, as well as the influence of gender, intellectual disability (ID), age, and autism spectrum disorder (ASD) diagnosis. Methods: Data were drawn from the 975 participants who have a completed clinician form. We explored the frequency of psychotropic medication use for the following symptom clusters: attention, hyperactivity, anxiety, hypersensitivity, obsessive-compulsive disorder (OCD), mood swings, irritability/agitation, aggression, and self-injury (IAAS). Results: A majority of participants (617 or 63.3%) were taking a psychotropic medication, including investigational drugs. Medications were often targeting multiple symptoms. Psychotropic medication use was more common in males, adolescents, and those with comorbid ID and ASD. Anxiety was the most frequently targeted symptom, followed by attention-deficit/hyperactivity disorder symptoms and IAAS. Selective serotonin reuptake inhibitors (SSRIs) were the most frequently prescribed medication class among all patients (n = 266, 43%), followed by stimulants (n = 235, 38%), each with no gender difference. Antipsychotics were the third most frequently prescribed medication class (n = 205, 33%), and were more frequently prescribed to males and those with ID and ASD. Conclusions: Anxiety, attention and hyperactivity were the most common symptom targets for psychopharmacologic intervention in FXS. Our results support clinical knowledge that males with comorbid ASD and ID have a more severe presentation requiring more intervention including medications. These results highlight the need for examination of symptom overlap and interaction.

FMRP Levels in Human Peripheral Blood Leukocytes Correlates with Intellectual Disability

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability. FXS is an X-linked, neurodevelopmental disorder caused by a CGG trinucleotide repeat expansion in the 5′ untranslated region (UTR) of the Fragile X Mental Retardation gene, FMR1. Greater than 200 CGG repeats results in epigenetic silencing of the gene leading to the deficiency or absence of Fragile X mental retardation protein (FMRP). The loss of FMRP is considered the root cause of FXS. The relationship between neurological function and FMRP expression in peripheral blood mononuclear cells (PBMCs) has not been well established. Assays to detect and measure FMR1 and FMRP have been described; however, none are sufficiently sensitive, precise, or quantitative to properly characterize the relationships between cognitive ability and CGG repeat number, FMR1 mRNA expression, or FMRP expression measured in PBMCs. To address these limitations, two novel immunoassays were developed and optimized, an electro-chemiluminescence immunoassay and a multiparameter flow cytometry assay. Both assays were performed on PMBCs isolated from 27 study participants with FMR1 CGG repeats ranging from normal to full mutation. After correcting for methylation, a significant positive correlation between CGG repeat number and FMR1 mRNA expression levels and a significant negative correlation between FMRP levels and CGG repeat expansion was observed. Importantly, a high positive correlation was observed between intellectual quotient (IQ) and FMRP expression measured in PBMCs.

A white paper on a neurodevelopmental framework for drug discovery in autism and other neurodevelopmental disorders

In the last decade there has been a revolution in terms of genetic findings in neurodevelopmental disorders (NDDs), with many discoveries critical for understanding their aetiology and pathophysiology. Clinical trials in single-gene disorders such as fragile X syndrome highlight the challenges of investigating new drug targets in NDDs. Incorporating a developmental perspective into the process of drug development for NDDs could help to overcome some of the current difficulties in identifying and testing new treatments. This paper provides a summary of the proceedings of the 'New Frontiers Meeting' on neurodevelopmental disorders organised by the European College of Neuropsychopharmacology in conjunction with the Innovative Medicines Initiative-sponsored AIMS-2-TRIALS consortium. It brought together experts in developmental genetics, autism, NDDs, and clinical trials from academia and industry, regulators, patient and family associations, and other stakeholders. The meeting sought to provide a platform for focused communication on scientific insights, challenges, and methodologies that might be applicable to the development of CNS treatments from a neurodevelopmental perspective. Multidisciplinary translational consortia to develop basic and clinical research in parallel could be pivotal to advance knowledge in the field. Although implementation of clinical trials for NDDs in paediatric populations is widely acknowledged as essential, safety concerns should guide each aspect of their design. Industry and academia should join forces to improve knowledge of the biology of brain development, identify the optimal timing of interventions, and translate these findings into new drugs, allowing for the needs of users and families, with support from regulatory agencies.

Lithium as a possible therapeutic strategy for Cornelia de Lange syndrome

Cornelia de Lange Syndrome (CdLS) is a rare developmental disorder affecting a multitude of organs including the central nervous system, inducing a variable neurodevelopmental delay. CdLS malformations derive from the deregulation of developmental pathways, inclusive of the canonical WNT pathway. We have evaluated MRI anomalies and behavioral and neurological clinical manifestations in CdLS patients. Importantly, we observed in our cohort a significant association between behavioral disturbance and structural abnormalities in brain structures of hindbrain embryonic origin. Considering the cumulative evidence on the cohesin-WNT-hindbrain shaping cascade, we have explored possible ameliorative effects of chemical activation of the canonical WNT pathway with lithium chloride in different models: (I) Drosophila melanogaster CdLS model showing a significant rescue of mushroom bodies morphology in the adult flies; (II) mouse neural stem cells restoring physiological levels in proliferation rate and differentiation capabilities toward the neuronal lineage; (III) lymphoblastoid cell lines from CdLS patients and healthy donors restoring cellular proliferation rate and inducing the expression of CyclinD1. This work supports a role for WNT-pathway regulation of CdLS brain and behavioral abnormalities and a consistent phenotype rescue by lithium in experimental models.

Neuroimaging Insight Into Fragile X-Associated Neuropsychiatric Disorders: Literature Review

FMR1 premutation is defined by 55-200 CGG repeats in the Fragile X Mental Retardation 1 (FMR1) gene. FMR1 premutation carriers are at risk of developing a neurodegenerative disease called fragile X-associated tremor/ataxia syndrome (FXTAS) and Fragile X-associated primary ovarian insufficiency (FXPOI) in adulthood. In the last years an increasingly board spectrum of clinical manifestations including psychiatric disorders have been described as occurring at a greater frequency among FMR1 premutation carriers. Herein, we reviewed the neuroimaging findings reported in relation with psychiatric symptomatology in adult FMR1 premutation carriers. A structured electronic literature search was conducted on FMR1 premutation and neuroimaging yielding a total of 3,229 articles examined. Of these, 7 articles were analyzed and are included in this review. The results showed that the main radiological findings among adult FMR1 premutation carriers presenting neuropsychiatric disorders were found on the amygdala and hippocampus, being the functional abnormalities more consistent and the volumetric changes more inconsistent among studies. From a molecular perspective, CGG repeat size, FMR1 mRNA and FMRP levels have been investigated in relation with the neuroimaging findings. Based on the published results, FMRP might play a key role in the pathophysiology of the psychiatric symptoms described among FMR1 premutation carriers. However, additional studies including further probes of brain function and a broader scope of psychiatric symptom measurement are required in order to obtain a comprehensive landscape of the neuropsychiatric phenotype associated with the FMR1 premutation.

A Genotype-Phenotype Study of High-Resolution FMR1 Nucleic Acid and Protein Analyses in Fragile X Patients with Neurobehavioral Assessments

Fragile X syndrome (FXS) is caused by silencing of the FMR1 gene, which encodes a protein with a critical role in synaptic plasticity. The molecular abnormality underlying FMR1 silencing, CGG repeat expansion, is well characterized; however, delineation of the pathway from DNA to RNA to protein using biosamples from well characterized patients with FXS is limited. Since FXS is a common and prototypical genetic disorder associated with intellectual disability (ID) and autism spectrum disorder (ASD), a comprehensive assessment of the FMR1 DNA-RNA-protein pathway and its correlations with the neurobehavioral phenotype is a priority. We applied nine sensitive and quantitative assays evaluating FMR1 DNA, RNA, and FMRP parameters to a reference set of cell lines representing the range of FMR1 expansions. We then used the most informative of these assays on blood and buccal specimens from cohorts of patients with different FMR1 expansions, with emphasis on those with FXS (N = 42 total, N = 31 with FMRP measurements). The group with FMRP data was also evaluated comprehensively in terms of its neurobehavioral profile, which allowed molecular-neurobehavioral correlations. FMR1 CGG repeat expansions, methylation levels, and FMRP levels, in both cell lines and blood samples, were consistent with findings of previous FMR1 genomic and protein studies. They also demonstrated a high level of agreement between blood and buccal specimens. These assays further corroborated previous reports of the relatively high prevalence of methylation mosaicism (slightly over 50% of the samples). Molecular-neurobehavioral correlations confirmed the inverse relationship between overall severity of the FXS phenotype and decrease in FMRP levels (N = 26 males, mean 4.2 ± 3.3 pg FMRP/ng genomic DNA). Other intriguing findings included a significant relationship between the diagnosis of FXS with ASD and two-fold lower levels of FMRP (mean 2.8 ± 1.3 pg FMRP/ng genomic DNA, p = 0.04), in particular observed in younger age- and IQ-adjusted males (mean age 6.9 ± 0.9 years with mean 3.2 ± 1.2 pg FMRP/ng genomic DNA, 57% with severe ASD), compared to FXS without ASD. Those with severe ID had even lower FMRP levels independent of ASD status in the male-only subset. The results underscore the link between FMR1 expansion, gene methylation, and FMRP deficit. The association between FMRP deficiency and overall severity of the neurobehavioral phenotype invites follow up studies in larger patient cohorts. They would be valuable to confirm and potentially extend our initial findings of the relationship between ASD and other neurobehavioral features and the magnitude of FMRP deficit. Molecular profiling of individuals with FXS may have important implications in research and clinical practice.

Dynamics of the fragile X mental retardation protein correlates with cellular and synaptic properties in primary auditory neurons following afferent deprivation

Afferent activity dynamically regulates neuronal properties and connectivity in the central nervous system. The Fragile X mental retardation protein (FMRP) is an RNA-binding protein that regulates cellular and synaptic properties in an activity-dependent manner. Whether and how FMRP level and localization are regulated by afferent input remains sparsely examined and how such regulation is associated with neuronal response to changes in sensory input is unknown. We characterized changes in FMRP level and localization in the chicken nucleus magnocellularis (NM), a primary cochlear nucleus, following afferent deprivation by unilateral cochlea removal. We observed rapid (within 2 hr) aggregation of FMRP immunoreactivity into large granular structures in a subset of deafferented NM neurons. Neurons that exhibited persistent FMRP aggregation at 12-24 hr eventually lost cytoplasmic Nissl substance, indicating cell death. A week later, FMRP expression in surviving neurons regained its homeostasis, with a slightly reduced immunostaining intensity and enhanced heterogeneity. Correlation analyses under the homeostatic status (7-14 days) revealed that neurons expressing relatively more FMRP had a higher capability of maintaining cell body size and ribosomal activity, as well as a better ability to detach inactive presynaptic terminals. Additionally, the intensity of an inhibitory postsynaptic protein, gephyrin, was reduced following deafferentation and was positively correlated with FMRP intensity, implicating an involvement of FMRP in synaptic dynamics in response to reduced afferent inputs. Collectively, this study demonstrates that afferent input regulates FMRP expression and localization in ways associated with multiple types of neuronal responses and synaptic rearrangements.

Association between IQ and FMR1 protein (FMRP) across the spectrum of CGG repeat expansions

Fragile X syndrome, the leading heritable form of intellectual disability, is caused by hypermethylation and transcriptional silencing of large (CGG) repeat expansions (> 200 repeats) in the 5′ untranslated region of the fragile X mental retardation 1 (FMR1) gene. As a consequence of FMR1 gene silencing, there is little or no production of FMR1 protein (FMRP), an important element in normal synaptic function. Although the absence of FMRP has long been known to be responsible for the cognitive impairment in fragile X syndrome, the relationship between FMRP level and cognitive ability (IQ) is only imprecisely understood. To address this issue, a high-throughput, fluorescence resonance energy transfer (FRET) assay has been used to quantify FMRP levels in dermal fibroblasts, and the relationship between FMRP and IQ measures was assessed by statistical analysis in a cohort of 184 individuals with CGG-repeat lengths spanning normal (< 45 CGGs) to full mutation (> 200 CGGs) repeat ranges in fibroblasts. The principal findings of the current study are twofold: i) For those with normal CGG repeats, IQ is no longer sensitive to further increases in FMRP above an FMRP threshold of ~70% of the mean FMRP level; below this threshold, IQ decreases steeply with further decreases in FMRP; and ii) For the current cohort, a mean IQ of 85 (lower bound for the normal IQ range) is attained for FMRP levels that are only ~35% of the mean FMRP level among normal CGG-repeat controls. The current results should help guide expectations for efforts to induce FMR1 gene activity and for the levels of cognitive function expected for a given range of FMRP levels.

Lmtk3-KO Mice Display a Range of Behavioral Abnormalities and Have an Impairment in GluA1 Trafficking

Accumulating evidence suggests that glutamatergic signaling and synaptic plasticity underlie one of a number of ways psychiatric disorders appear. The present study reveals a possible mechanism by which this occurs, through highlighting the importance of LMTK3, in the brain. Behavioral analysis of Lmtk3-KO mice revealed a number of abnormalities that have been linked to psychiatric disease such as hyper-sociability, PPI deficits and cognitive dysfunction. Treatment with clozapine suppressed these behavioral changes in Lmtk3-KO mice. As synaptic dysfunction is implicated in human psychiatric disease, we analyzed the LTP of Lmtk3-KO mice and found that induction is severely impaired. Further investigation revealed abnormalities in GluA1 trafficking after AMPA stimulation in Lmtk3-KO neurons, along with a reduction in GluA1 expression in the post-synaptic density. Therefore, we hypothesize that LMTK3 is an important factor involved in the trafficking of GluA1 during LTP, and that disruption of this pathway contributes to the appearance of behavior associated with human psychiatric disease in mice.

Are FXR Family Proteins Integrators of Dopamine Signaling and Glutamatergic Neurotransmission in Mental Illnesses?

Dopamine receptors and related signaling pathways have long been implicated in pathophysiology and treatment of mental illnesses, including schizophrenia and bipolar disorder. Dopamine signaling may impact neuronal activity by modulation of glutamate neurotransmission. Recent evidence indicates a direct and/or indirect involvement of fragile X-related family proteins (FXR) in the regulation and mediation of dopamine receptor functions. FXRs consists of fragile X mental retardation protein 1 (Fmr1/FMRP) and its autosomal homologs Fxr1 and Fxr2. These RNA-binding proteins are enriched in the brain. Loss of function mutation in human FMR1 is the major genetic contributor to Fragile X mental retardation syndrome. Therefore, the role of FXR proteins has mostly been studied in the context of autism spectrum disorders. However, recent genome-wide association studies have linked this family to schizophrenia, bipolar disorders, and mood regulation pointing toward a broader involvement in mental illnesses. FXR family proteins play an important role in the regulation of glutamate-mediated neuronal activity and plasticity. Here, we discuss the brain-specific functions of FXR family proteins by focusing on the regulation of dopamine receptor functions, ionotropic glutamate receptors-mediated synaptic plasticity and contribution to mental illnesses. Based on recent evidence, we propose that FXR proteins are potential integrators of dopamine signaling and ionotropic glutamate transmission.

Spectral and temporal properties of calls reveal deficits in ultrasonic vocalizations of adult Fmr1 knockout mice

The Fmr1 knockout (KO) mouse has commonly been used to investigate communication impairments, one of the key diagnostic symptoms observed in Fragile X syndrome (FXS) and Autism spectrum disorder (ASD). Many studies have found alterations in ultrasonic vocalizations (USVs) in neonatal Fmr1 KO mice, however, there is limited research investigating whether these deficits continue into adulthood. In the present study, we examine differences in female urine-induced ultrasonic vocalizations, scent marking behavior, odor discrimination, and open field activity in adult male Fmr1 KO and wildtype (WT) mice. Overall, we found extensive alterations between genotypes in both spectral and temporal properties of ultrasonic vocalizations. There was no difference in the average number of calls emitted by both genotypes, however, Fmr1 KO mice emitted calls of a higher frequency, decreased amplitude, and shorter duration than WT mice. Spectrographic analyses revealed statistically significant differences between genotypes in the types of calls emitted. Contrastingly, we found no differences in scent marking behavior, a form of social communication, or in odor discrimination and activity levels of the mice. The results corroborate previous studies emphasizing the importance of qualitative differences observed in vocalization behavior of Fmr1 KO mice, rather than quantitative measurements such as number of calls emitted. Overall, the study confirms the presence of abnormalities in vocalization behavior in adult Fmr1 KO mice that we believe are consistent with communication deficits seen in the syndrome.

Genetic Consideration of Schizotypal Traits: A Review

Schizotypal traits are of interest and importance in their own right and also have theoretical and clinical associations with schizophrenia. These traits comprise attenuated psychotic symptoms, social withdrawal, reduced cognitive capacity, and affective dysregulation. The link between schizotypal traits and psychotic disorders has long since been debated. The status of knowledge at this point is such schizotypal traits are a risk for psychotic disorders, but in and of themselves only confer liability, with other risk factors needing to be present before a transition to psychosis occurs. Investigation of schizotypal traits also has the possibility to inform clinical and research pursuits concerning those who do not make a transition to psychotic disorders. A growing body of literature has investigated the genetic underpinnings of schizotypal traits. Here, we review association, family studies and describe genetic disorders where the expression of schizotypal traits has been investigated. We conducted a thorough review of the existing literature, with multiple search engines, references, and linked articles being searched for relevance to the current review. All articles and book chapters in English were sourced and reviewed for inclusion. Family studies demonstrate that schizotypal traits are elevated with increasing genetic proximity to schizophrenia and some chromosomal regions have been associated with schizotypy. Genes associated with schizophrenia have provided the initial start point for the investigation of candidate genes for schizotypal traits; neurobiological pathways of significance have guided selection of genes of interest. Given the chromosomal regions associated with schizophrenia, some genetic disorders have also considered the expression of schizotypal traits. Genetic disorders considered all comprise a profile of cognitive deficits and over representation of psychotic disorders compared to the general population. We conclude that genetic variations associated with schizotypal traits require further investigation, perhaps with targeted phenotypes narrowed to assist in refining the clinical end point of significance.

Challenges in understanding psychiatric disorders and developing therapeutics: a role for zebrafish

The treatment of psychiatric disorders presents three major challenges to the research and clinical community: defining a genotype associated with a disorder, characterizing the molecular pathology of each disorder and developing new therapies. This Review addresses how cellular and animal systems can help to meet these challenges, with an emphasis on the role of the zebrafish. Genetic changes account for a large proportion of psychiatric disorders and, as gene variants that predispose to psychiatric disease are beginning to be identified in patients, these are tractable for study in cellular and animal systems. Defining cellular and molecular criteria associated with each disorder will help to uncover causal physiological changes in patients and will lead to more objective diagnostic criteria. These criteria should also define co-morbid pathologies within the nervous system or in other organ systems. The definition of genotypes and of any associated pathophysiology is integral to the development of new therapies. Cell culture-based approaches can address these challenges by identifying cellular pathology and by high-throughput screening of gene variants and potential therapeutics. Whole-animal systems can define the broadest function of disorder-associated gene variants and the organismal impact of candidate medications. Given its evolutionary conservation with humans and its experimental tractability, the zebrafish offers several advantages to psychiatric disorder research. These include assays ranging from molecular to behavioural, and capability for chemical screening. There is optimism that the multiple approaches discussed here will link together effectively to provide new diagnostics and treatments for psychiatric patients.

Summary: In this review, we discuss strengths and limitations of prevalent laboratory models that are used for understanding psychiatric disorders and developing therapeutics, with emphasis on the zebrafish.

Fragile X Mental Retardation Protein expression in the retina is regulated by light

Fragile X Mental Retardation Protein (FMRP) is a RNA-binding protein that modulates protein synthesis at the synapse and its function is regulated by glutamate. The retina is the first structure that participates in vision, and uses glutamate to transduce electromagnetic signals from light to electrochemical signals to neurons. FMRP has been previously detected in the retina, but its localization has not been studied yet. In this work, our objectives were to describe the localization of FMRP in the retina, to determine whether different exposure to dark or light stimulus alters FMRP expression in the retina, and to compare the pattern in two different species, the mouse and chick. We found that both FMRP mRNA and protein are expressed in the retina. By immunohistochemistry analysis we found that both mouse and chick present similar FMRP expression localized mainly in both plexiform layers and the inner retina. It was also observed that FMRP is down-regulated by 24 h dark adaptation compared to its expression in the retina of animals that were exposed to light for 1 h after 24 h in the dark. We conclude that FMRP is likely to participate in retinal physiology, since its expression changes with light exposure. In addition, the expression pattern and regulation by light of FMRP seems well conserved since it was similar in both mouse and chick.

Psychosis and catatonia in fragile X: Case report and literature review

Fragile X mental retardation 1 (FMR1) premutation associated phenotypes have been explored extensively since the molecular mechanism emerged involving elevated FMR1 messenger ribonucleic acid (mRNA) levels. Lowered fragile X mental retardation protein (FMRP) can also occur which may have an additive effect to the high levels of mRNA leading to neurodevelopmental problems and psychopathology. This paper was aimed to review psychosis and catatonia in premutation carriers, express the role of elevated FMR1 mRNA and lowered FMRP in the phenotype of carriers and present a case of psychosis and catatonia in a carrier. This case also demonstrates additional genetic and environmental factors which may also affect the phenotype. We review the literature and report an exemplary case of a 25 year old male premutation carrier with elevated FMR1 mRNA, low FMRP, a cytochrome P450 family 2 subfamily D polypeptide 6 (CYP2D6)*2xN mutation and a perinatal insult. This patient developed an autism spectrum disorder, psychosis, catatonia with subsequent cognitive decline after electro-convulsive therapy (ECT) for his catatonia. He had a premutation of 72 CGG repeat in FMR1, FMR1 mRNA level that was over 2.4 times normal and FMRP level at 18% of normal, and additionally, a CYP2D6 allelic variant which leads to ultrarapid metabolism (UM) of medication. There is an overlapping pathophysiological mechanism of catatonia and fragile X-associated premutation phenotypes including autism and psychosis. This case demonstrates the shared phenotype and the overlap of the pathophysiological mechanisms that can influence the intervention. Multiple genetic and environmental hits can lead to more significant involvement in premutation carriers.

Molecular underpinnings of prefrontal cortex development in rodents provide insights into the etiology of neurodevelopmental disorders

The prefrontal cortex (PFC), seat of the highest-order cognitive functions, constitutes a conglomerate of highly specialized brain areas and has been implicated to have a role in the onset and installation of various neurodevelopmental disorders. The development of a properly functioning PFC is directed by transcription factors, guidance cues and other regulatory molecules and requires the intricate and temporal orchestration of a number of developmental processes. Disturbance or failure of any of these processes causing neurodevelopmental abnormalities within the PFC may contribute to several of the cognitive deficits seen in patients with neurodevelopmental disorders. In this review, we elaborate on the specific processes underlying prefrontal development, such as induction and patterning of the prefrontal area, proliferation, migration and axonal guidance of medial prefrontal progenitors, and their eventual efferent and afferent connections. We furthermore integrate for the first time the available knowledge from genome-wide studies that have revealed genes linked to neurodevelopmental disorders with experimental molecular evidence in rodents. The integrated data suggest that the pathogenic variants in the neurodevelopmental disorder-associated genes induce prefrontal cytoarchitectonical impairments. This enhances our understanding of the molecular mechanisms of prefrontal (mis)development underlying the four major neurodevelopmental disorders in humans, that is, intellectual disability, autism spectrum disorders, attention deficit hyperactivity disorder and schizophrenia, and may thus provide clues for the development of novel therapies.

Reduced phenotypic severity following adeno-associated virus-mediated Fmr1 gene delivery in fragile X mice

Fragile X syndrome (FXS) is a neurodevelopmental disorder caused by a trinucleotide repeat expansion in the FMR1 gene that codes for fragile X mental retardation protein (FMRP). To determine if FMRP expression in the central nervous system could reverse phenotypic deficits in the Fmr1 knockout (KO) mouse model of FXS, we used a single-stranded adeno-associated viral (AAV) vector with viral capsids from serotype 9 that contained a major isoform of FMRP. FMRP transgene expression was driven by the neuron-selective synapsin-1 promoter. The vector was delivered to the brain via a single bilateral intracerebroventricular injection into neonatal Fmr1 KO mice and transgene expression and behavioral assessments were conducted 22-26 or 50-56 days post injection. Western blotting and immunocytochemical analyses of AAV-FMRP-injected mice revealed FMRP expression in the striatum, hippocampus, retrosplenial cortex, and cingulate cortex. Cellular expression was selective for neurons and reached ∼ 50% of wild-type levels in the hippocampus and cortex at 56 days post injection. The pathologically elevated repetitive behavior and the deficit in social dominance behavior seen in phosphate-buffered saline-injected Fmr1 KO mice were reversed in AAV-FMRP-injected mice. These results provide the first proof of principle that gene therapy can correct specific behavioral abnormalities in the mouse model of FXS.

Place field stability requires the metabotropic glutamate receptor, mGlu5

The metabotropic glutamate (mGlu) receptors are critically involved in enabling the persistency of forms of synaptic plasticity that are believed to underlie hippocampus-dependent memory. These receptors and in particular, mGlu5, are also required for hippocampus-dependent learning and memory. In the hippocampus, synaptic plasticity is one of the mechanisms by which spatial information may be represented. Another mechanism involves increased firing of place cells. Place cells increase their firing activity when an animal is in a specific spatial location. Inhibition of factors that are essential for synaptic plasticity, such as N-methyl-d-aspartate receptors or protein synthesis, also impair place cell activity. This raises the question as to whether mGlu receptors, that are so important for synaptic plasticity and spatial memory, are also important for place cell encoding. We examined location-dependent place cell firing i.e. place fields. We observed that antagonism of mGlu5, using 2-methyl-6-(phenylethynyl) pyridine (MPEP) had no effect on place field profiles in a familiar environment. However, in a novel environment mGlu5-antagonism affected long-term place field stability, reduced place cell firing and spatial information. These data strongly suggest a role for mGlu5 in the mechanisms underlying informational content and long-term stability of place fields, and add to evidence supporting the importance of these receptors for hippocampal function.

2-Methyl-6-(phenylethynyl) pyridine (MPEP) reverses maze learning and PSD-95 deficits in Fmr1 knock-out mice

Fragile X Syndrome (FXS) is caused by the lack of expression of the fragile X mental retardation protein (FMRP), which results in intellectual disability and other debilitating symptoms including impairment of visual-spatial functioning. FXS is the only single-gene disorder that is highly co-morbid with autism spectrum disorder and can therefore provide insight into its pathophysiology. Lack of FMRP results in altered group I metabotropic glutamate receptor (mGluR) signaling, which is a target for putative treatments. The Hebb-Williams (H-W) mazes are a set of increasingly complex spatial navigation problems that depend on intact hippocampal and thus mGluR-5 functioning. In the present investigation, we examined whether an antagonist of mGluR-5 would reverse previously described behavioral deficits in fragile X mental retardation 1 knock-out (Fmr1 KO) mice. Mice were trained on a subset of the H-W mazes and then treated with either 20 mg/kg of an mGluR-5 antagonist, 2-Methyl-6-(phenylethynyl) pyridine (MPEP; n = 11) or an equivalent dose of saline (n = 11) prior to running test mazes. Latency and errors were dependent variables recorded during the test phase. Immediately after completing each test, marble-burying behavior was assessed, which confirmed that the drug treatment was pharmacologically active during maze learning. Although latency was not statistically different between the groups, MPEP treated Fmr1 KO mice made significantly fewer errors on mazes deemed more difficult suggesting a reversal of the behavioral deficit. MPEP treated mice were also less perseverative and impulsive when navigating mazes. Furthermore, MPEP treatment reversed post-synaptic density-95 (PSD-95) protein deficits in Fmr1 KO treated mice, whereas levels of a control protein (β-tubulin) remained unchanged. These data further validate MPEP as a potentially beneficial treatment for FXS. Our findings also suggest that adapted H-W mazes may be a useful tool to document alterations in behavioral functioning following pharmacological intervention in FXS.

Neuregulin 1-induced AKT and ERK phosphorylation in patients with fragile X syndrome (FXS) and intellectual disability associated with obstetric complications

Animal models of fragile X syndrome (FXS) suggest the impairment of the intracellular AKT messenger system, which is activated by neuregulin 1 (NRG1), a key regulator of neurodevelopment. We investigated NRG1-induced activation of the AKT and extracellular signal-regulated kinase (ERK) systems by the measurement of the phosphorylated AKT/ERK to total AKT/ERK ratio in peripheral B lymphoblasts of patients with FXS, IQ-matched controls with intellectual disability (obstetric complications, preterm birth, perinatal hypoxia, and low birth weight), and typically developed healthy participants. Results revealed that patients with FXS displayed decreased AKT but normal ERK activation after the administration of NRG1. IQ-matched controls with intellectual disability displayed intact AKT/ERK activation. In conclusion, FXS, but not intellectual disability associated with obstetric complications, is associated with decreased NRG1-induced AKT phosphorylation.

Impaired activity-dependent neural circuit assembly and refinement in autism spectrum disorder genetic models

Early-use activity during circuit-specific critical periods refines brain circuitry by the coupled processes of eliminating inappropriate synapses and strengthening maintained synapses. We theorize these activity-dependent (A-D) developmental processes are specifically impaired in autism spectrum disorders (ASDs). ASD genetic models in both mouse and Drosophila have pioneered our insights into normal A-D neural circuit assembly and consolidation, and how these developmental mechanisms go awry in specific genetic conditions. The monogenic fragile X syndrome (FXS), a common cause of heritable ASD and intellectual disability, has been particularly well linked to defects in A-D critical period processes. The fragile X mental retardation protein (FMRP) is positively activity-regulated in expression and function, in turn regulates excitability and activity in a negative feedback loop, and appears to be required for the A-D remodeling of synaptic connectivity during early-use critical periods. The Drosophila FXS model has been shown to functionally conserve the roles of human FMRP in synaptogenesis, and has been centrally important in generating our current mechanistic understanding of the FXS disease state. Recent advances in Drosophila optogenetics, transgenic calcium reporters, highly-targeted transgenic drivers for individually-identified neurons, and a vastly improved connectome of the brain are now being combined to provide unparalleled opportunities to both manipulate and monitor A-D processes during critical period brain development in defined neural circuits. The field is now poised to exploit this new Drosophila transgenic toolbox for the systematic dissection of A-D mechanisms in normal versus ASD brain development, particularly utilizing the well-established Drosophila FXS disease model.

Exploring inhibitory deficits in female premutation carriers of fragile X syndrome: through eye movements

There is evidence which demonstrates that a subset of males with a premutation CGG repeat expansion (between 55 and 200 repeats) of the fragile X mental retardation 1 gene exhibit subtle deficits of executive function that progressively deteriorate with increasing age and CGG repeat length. However, it remains unclear whether similar deficits, which may indicate the onset of more severe degeneration, are evident in female PM-carriers. In the present study we explore whether female PM-carriers exhibit deficits of executive function which parallel those of male PM-carriers. Fourteen female fragile X premutation carriers without fragile X-associated tremor/ataxia syndrome and fourteen age, sex, and IQ matched controls underwent ocular motor and neuropsychological tests of select executive processes, specifically of response inhibition and working memory. Group comparisons revealed poorer inhibitory control for female premutation carriers on ocular motor tasks, in addition to demonstrating some difficulties in behaviour self-regulation, when compared to controls. A negative correlation between CGG repeat length and antisaccade error rates for premutation carriers was also found. Our preliminary findings indicate that impaired inhibitory control may represent a phenotype characteristic which may be a sensitive risk biomarker within this female fragile X premutation population.

Molecular Advances Leading to Treatment Implications for Fragile X Premutation Carriers

Fragile X syndrome (FXS) is the most common single gene cause of intellectual disability and it is characterized by a CGG expansion of more than 200 repeats in the FMR1 gene, leading to methylation of the promoter and gene silencing. The fragile X premutation, characterized by a 55 to 200 CGG repeat expansion, causes health problems and developmental difficulties in some, but not all, carriers. The premutation causes primary ovarian insufficiency in approximately 20% of females, psychiatric problems (including depression and/or anxiety) in approximately 50% of carriers and a neurodegenerative disorder, the fragile X-associated tremor ataxia syndrome (FXTAS), in approximately 40% of males and 16% of females later in life. Recent clinical studies in premutation carriers have expanded the health problems that may be seen. Advances in the molecular pathogenesis of the premutation have shown significant mitochondrial dysfunction and oxidative stress in neurons which may be amenable to treatment. Here we review the clinical problems of carriers and treatment recommendations.

Decreased fragile X mental retardation protein (FMRP) is associated with lower IQ and earlier illness onset in patients with schizophrenia

The purpose of this study was to investigate Fragile X Syndrome (FXS)-related mechanisms in schizophrenia, including CGG triplet expansion, FMR1 mRNA, and fragile X mental retardation protein (FMRP) levels in lymphocytes. We investigated 36 patients with schizophrenia and 30 healthy controls using Southern blot analysis, mRNA assay, and enzyme-linked immunosorbent assay (ELISA). General intellectual functions were assessed with the Wechsler Adult Intelligence Scale-III, and the clinical symptoms were evaluated with the Positive and Negative Syndrome Scale. Results revealed that, relative to healthy controls, CGG triplet size and FMR1 mRNA were unaltered in patients with schizophrenia. However, the FMRP level was significantly reduced in patients compared with controls. We found an association between lower FMRP levels, reduced IQ, and earlier illness onset in schizophrenia. Chlorpromazine-equivalent antipsychotic dose did not correlate with FMRP levels. These results raise the possibility of impaired translation of FMR1 mRNA, altered epigenetic regulation, or increased degradation of FMRP in schizophrenia, which may play a role in dysfunctional neurodevelopmental processes and impaired neuroplasticity.

Contrast, motion, perceptual integration, and neurocognition in schizophrenia: the role of fragile-X related mechanisms

Recent studies demonstrated a reduced expression of Fragile X Mental Retardation Protein (FMRP), an RNA binding protein and translation regulator, in the brain and peripheral lymphocytes of patients with schizophrenia. Low FMRP levels may be related to impaired neurodevelopmental processes and synaptic plasticity. Here, we studied the relationship between peripheral FMRP level, visual perception (contrast sensitivity, perceptual integration, motion/form perception), and neuropsychological functions in schizophrenia as measured with the Repeatable Battery for the Assessment of Neuropsychological Status (RBANS). Results revealed that patients with schizophrenia displayed lower FMRP levels in peripheral lymphocytes as compared to control individuals. We found significant correlations between FMRP levels and contrast sensitivity at low spatial and high temporal frequencies, perceptual integration, and motion perception. The relationship between FMRP level and neuropsychological functions was less pronounced than that seen in the case of visual perception, with the greatest effect for RBANS attention. FMRP level was not related to contrast sensitivity at high spatial and low temporal frequencies and form perception. This pattern of data is reminiscent to that observed in patients with Fragile X Syndrome (FXS). These results suggest that FMRP may be implicated in the pathogenesis of schizophrenia, possibly via the regulation of neurodevelopment, plasticity, GABA-ergic, and glutamatergic neurotransmission.

Early identification of autism in fragile X syndrome: a review

Fragile X syndrome (FXS) is the leading genetic cause of autism, accounting for approximately 5% of autism cases with as many as 50% of individuals with FXS meeting DSM-IV-TR criteria for autistic disorder. Both FXS and idiopathic autism (IA) are attributed to genetic causes; however, FXS is an identified single gene disorder whereas autism is a complex disorder with multiple potential causes, some of which have been identified. Studies in IA have focused on the prospective longitudinal examination of infant siblings of children with autism as a target group due to their high risk of developing the disorder. We propose that this same model be applied to the study of infants with FXS. There is a lack of research focusing on the early development of autism within FXS and debate in the literature regarding how to best conceptualise this co-morbidity or whether it should be considered a co-morbid condition at all. Studying the emergence and stability of autism in infants with FXS has multiple benefits such as clarifying the underlying mechanisms of the development of autism in FXS and solidifying similarities and differences between co-morbid FXS with autism and IA. Infant research in both IA and FXS are discussed as well as conclusions and implications for practice and future research.

Identification of expanded alleles of the FMR1 Gene in the CHildhood Autism Risks from Genes and Environment (CHARGE) study

Fragile X syndrome (FXS) is a neuro-developmental disorder characterized by intellectual disabilities and autism spectrum disorders (ASD). Expansion of a CGG trinucleotide repeat (>200 repeats) in the 5'UTR of the fragile X mental retardation gene, is the single most prevalent cause of cognitive disabilities. Several screening studies for FXS, among individuals with ID from different ethnic populations, have indicated that the prevalence of the syndrome varies between 0.5 and 16 %. Because the high co-morbidity with autism, we have conducted a screening study of the cohort from CHARGE, a large-scale, population-based, case control study. We have identified six subjects carrying an expanded allele, which emphasize the importance of screening for FXS in a population with intellectual disabilities and ASD.

Gene environment interaction studies in depression and suicidal behavior: An update

Increasing evidence supports the involvement of both heritable and environmental risk factors in major depression (MD) and suicidal behavior (SB). Studies investigating gene-environment interaction (G × E) may be useful for elucidating the role of biological mechanisms in the risk for mental disorders. In the present paper, we review the literature regarding the interaction between genes modulating brain functions and stressful life events in the etiology of MD and SB and discuss their potential added benefit compared to genetic studies only. Within the context of G × E investigation, thus far, only a few reliable results have been obtained, although some genes have consistently shown interactive effects with environmental risk in MD and, to a lesser extent, in SB. Further investigation is required to disentangle the direct and mediated effects that are common or specific to MD and SB. Since traditional G × E studies overall suffer from important methodological limitations, further effort is required to develop novel methodological strategies with an interdisciplinary approach.

Impairment of fragile X mental retardation protein-metabotropic glutamate receptor 5 signaling and its downstream cognates ras-related C3 botulinum toxin substrate 1, amyloid beta A4 precursor protein, striatal-enriched protein tyrosine phosphatase, and homer 1, in autism: a postmortem study in cerebellar vermis and superior frontal cortex

Background

Candidate genes associated with idiopathic forms of autism overlap with other disorders including fragile X syndrome. Our laboratory has previously shown reduction in fragile X mental retardation protein (FMRP) and increase in metabotropic glutamate receptor 5 (mGluR5) in cerebellar vermis and superior frontal cortex (BA9) of individuals with autism.

Methods

In the current study we have investigated expression of four targets of FMRP and mGluR5 signaling - homer 1, amyloid beta A4 precursor protein (APP), ras-related C3 botulinum toxin substrate 1 (RAC1), and striatal-enriched protein tyrosine phosphatase (STEP) - in the cerebellar vermis and superior frontal cortex (BA9) via SDS-PAGE and western blotting. Data were analyzed based on stratification with respect to age (children and adolescents vs. adults), anatomic region of the brain (BA9 vs. cerebellar vermis), and impact of medications (children and adolescents on medications (n = 4) vs. total children and adolescents (n = 12); adults on medications (n = 6) vs. total adults (n = 12)).

Results

There were significant increases in RAC1, APP 120 kDa and APP 80 kDa proteins in BA9 of children with autism vs. healthy controls. None of the same proteins were significantly affected in cerebellar vermis of children with autism. In BA9 of adults with autism there were significant increases in RAC1 and STEP 46 kDa and a significant decrease in homer 1 vs. controls. In the vermis of adult subjects with autism, RAC1 was significantly increased while APP 120, STEP 66 kDa, STEP 27 kDa, and homer 1 were significantly decreased when compared with healthy controls. No changes were observed in vermis of children with autism. There was a significant effect of anticonvulsant use on STEP 46 kDa/β-actin and a potential effect on homer 1/NSE, in BA9 of adults with autism. However, no other significant confound effects were observed in this study.

Conclusions

Our findings provide further evidence of abnormalities in FMRP and mGluR5 signaling partners in brains of individuals with autism and open the door to potential targeted treatments which could help ameliorate the symptoms of autism.

Effects of stimulus salience on touchscreen serial reversal learning in a mouse model of fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability in males and the most common genetic cause of autism. Although executive dysfunction is consistently found in humans with FXS, evidence of executive dysfunction in Fmr1 KO mice, a mouse model of FXS, has been inconsistent. One possible explanation for this is that executive dysfunction in Fmr1 KO mice, similar to humans with FXS, is only evident when cognitive demands are high. Using touchscreen operant conditioning chambers, male Fmr1 KO mice and their male wildtype littermates were tested on the acquisition of a pairwise visual discrimination followed by four serial reversals of the response rule. We assessed reversal learning performance under two different conditions. In the first, the correct stimulus was salient and the incorrect stimulus was non-salient. In the second and more challenging condition, the incorrect stimulus was salient and the correct stimulus was non-salient; this increased cognitive load by introducing conflict between sensory-driven (i.e., bottom-up) and task-dependent (i.e., top-down) signals. Fmr1 KOs displayed two distinct impairments relative to wildtype littermates. First, Fmr1 KOs committed significantly more learning-type errors during the second reversal stage, but only under high cognitive load. Second, during the first reversal stage, Fmr1 KOs committed significantly more attempts to collect a reward during the timeout following an incorrect response. These findings indicate that Fmr1 KO mice display executive dysfunction that, in some cases, is only evident under high cognitive load.

Relationships between age and epi-genotype of the FMR1 exon 1/intron 1 boundary are consistent with non-random X-chromosome inactivation in FM individuals, with the selection for the unmethylated state being most significant between birth and puberty

Methylation of the fragile X-related epigenetic element 2 (FREE2) located on the exon 1/intron 1 boundary of the FMR1 gene is related to FMRP expression and cognitive impairment in full mutation (FM; CGG>200) individuals. We examined the relationship between age, the size of the FMR1 CGG expansion and the methylation output ratio (MOR) at 12 CpG sites proximal to the exon 1/intron 1 boundary using FREE2 MALDI-TOF MS. The patient cohort included 119 males and 368 females, i.e. 121 healthy controls (CGG<40), 176 premutation (CGG 55-170) and 190 FM (CGG 213-2000). For all CpG units examined, FM males showed a significantly elevated MOR compared with that in hypermethylated FM females. In FM males the MOR for most CpG units significantly positively correlated with both age and CGG size (P< 0.05). In FM females the skewing towards the unmethylated state was significant for half of the units between birth and puberty (P < 0.05). The methylation status of intron 1 CpG10-12 that was most significantly related to cognitive impairment in our earlier study, did not change significantly with age in FM females. These results challenge the concept of fragile X syndrome (FXS)-related methylation being static over time, and suggest that due to the preference for the unmethylated state in FM females, X-inactivation at this locus is not random. The findings also highlight that the prognostic value of FXS methylation testing is not uniform between all CpG sites, and thus may need to be evaluated on a site-by-site basis.

DNA methylation and its basic function

In the mammalian genome, DNA methylation is an epigenetic mechanism involving the transfer of a methyl group onto the C5 position of the cytosine to form 5-methylcytosine. DNA methylation regulates gene expression by recruiting proteins involved in gene repression or by inhibiting the binding of transcription factor(s) to DNA. During development, the pattern of DNA methylation in the genome changes as a result of a dynamic process involving both de novo DNA methylation and demethylation. As a consequence, differentiated cells develop a stable and unique DNA methylation pattern that regulates tissue-specific gene transcription. In this chapter, we will review the process of DNA methylation and demethylation in the nervous system. We will describe the DNA (de)methylation machinery and its association with other epigenetic mechanisms such as histone modifications and noncoding RNAs. Intriguingly, postmitotic neurons still express DNA methyltransferases and components involved in DNA demethylation. Moreover, neuronal activity can modulate their pattern of DNA methylation in response to physiological and environmental stimuli. The precise regulation of DNA methylation is essential for normal cognitive function. Indeed, when DNA methylation is altered as a result of developmental mutations or environmental risk factors, such as drug exposure and neural injury, mental impairment is a common side effect. The investigation into DNA methylation continues to show a rich and complex picture about epigenetic gene regulation in the central nervous system and provides possible therapeutic targets for the treatment of neuropsychiatric disorders.

An epigenetic framework for neurodevelopmental disorders: from pathogenesis to potential therapy

Neurodevelopmental disorders (NDDs) are characterized by aberrant and delayed early-life development of the brain, leading to deficits in language, cognition, motor behaviour and other functional domains, often accompanied by somatic symptoms. Environmental factors like perinatal infection, malnutrition and trauma can increase the risk of the heterogeneous, multifactorial and polygenic disorders, autism and schizophrenia. Conversely, discrete genetic anomalies are involved in Down, Rett and Fragile X syndromes, tuberous sclerosis and neurofibromatosis, the less familiar Phelan-McDermid, Sotos, Kleefstra, Coffin-Lowry and "ATRX" syndromes, and the disorders of imprinting, Angelman and Prader-Willi syndromes. NDDs have been termed "synaptopathies" in reference to structural and functional disturbance of synaptic plasticity, several involve abnormal Ras-Kinase signalling ("rasopathies"), and many are characterized by disrupted cerebral connectivity and an imbalance between excitatory and inhibitory transmission. However, at a different level of integration, NDDs are accompanied by aberrant "epigenetic" regulation of processes critical for normal and orderly development of the brain. Epigenetics refers to potentially-heritable (by mitosis and/or meiosis) mechanisms controlling gene expression without changes in DNA sequence. In certain NDDs, prototypical epigenetic processes of DNA methylation and covalent histone marking are impacted. Conversely, others involve anomalies in chromatin-modelling, mRNA splicing/editing, mRNA translation, ribosome biogenesis and/or the regulatory actions of small nucleolar RNAs and micro-RNAs. Since epigenetic mechanisms are modifiable, this raises the hope of novel therapy, though questions remain concerning efficacy and safety. The above issues are critically surveyed in this review, which advocates a broad-based epigenetic framework for understanding and ultimately treating a diverse assemblage of NDDs ("epigenopathies") lying at the interface of genetic, developmental and environmental processes. This article is part of the Special Issue entitled 'Neurodevelopmental Disorders'.

Defining genetically meaningful language and personality traits in relatives of individuals with fragile X syndrome and relatives of individuals with autism

Substantial phenotypic overlap exists between fragile X syndrome (FXS) and autism, suggesting that FMR1 (the gene causing FXS) poses a significant risk for autism. Cross-population comparisons of FXS and autism therefore offer a potentially valuable method for refining the range of phenotypes associated with variation in FMR1. This study adopted a broader phenotype approach, focusing on parents who are at increased genetic liability for autism or FXS. Women who were carriers of FMR1 in its premutation state were compared with mothers of individuals with autism, and controls in an attempt to determine whether subtle features of the broad autism phenotype may express at elevated rates among FMR1 premutation carriers. The principal personality and language features comprising the broad autism phenotype (i.e., rigid and aloof personality, and particular patterns of pragmatic language use) were assessed among 49 premutation carriers who were mothers of individuals with FXS, 89 mothers of individuals with autism, and 23 mothers of typically developing individuals. Relative to controls, the autism and premutation parent groups showed elevated rates of certain personality and language characteristics of the broad autism phenotype. Findings suggest partially overlapping personality and language profiles among autism and premutation parent groups, with rigid personality style and patterns of pragmatic language use emerging as features most clearly shared between groups. These results provide further evidence for the overlap of autism and FXS, and may implicate FMR1 in some of the subtle features comprising the broad autism phenotype.

Consensus paper: pathological role of the cerebellum in autism

There has been significant advancement in various aspects of scientific knowledge concerning the role of cerebellum in the etiopathogenesis of autism. In the current consensus paper, we will observe the diversity of opinions regarding the involvement of this important site in the pathology of autism. Recent emergent findings in literature related to cerebellar involvement in autism are discussed, including: cerebellar pathology, cerebellar imaging and symptom expression in autism, cerebellar genetics, cerebellar immune function, oxidative stress and mitochondrial dysfunction, GABAergic and glutamatergic systems, cholinergic, dopaminergic, serotonergic, and oxytocin-related changes in autism, motor control and cognitive deficits, cerebellar coordination of movements and cognition, gene-environment interactions, therapeutics in autism, and relevant animal models of autism. Points of consensus include presence of abnormal cerebellar anatomy, abnormal neurotransmitter systems, oxidative stress, cerebellar motor and cognitive deficits, and neuroinflammation in subjects with autism. Undefined areas or areas requiring further investigation include lack of treatment options for core symptoms of autism, vermal hypoplasia, and other vermal abnormalities as a consistent feature of autism, mechanisms underlying cerebellar contributions to cognition, and unknown mechanisms underlying neuroinflammation.