Influence of stimulants on electrodermal studies in Fragile X syndrome

Targeted Treatments for Fragile X Syndrome

The histories of targeted treatment trials in fragile X syndrome (FXS) are reviewed in animal studies and human trials. Advances in understanding the neurobiology of FXS have identified a number of pathways that are dysregulated in the absence of FMRP and are therefore pathways that can be targeted with new medication. The utilization of quantitative outcome measures to assess efficacy in multiple studies has improved the quality of more recent trials. Current treatment trials including the use of cannabidiol (CBD) topically and metformin orally have positive preliminary data, and both of these medications are available clinically. The use of the phosphodiesterase inhibitor (PDE4D), BPN1440, which raised the level of cAMP that is low in FXS has very promising results for improving cognition in adult males who underwent a controlled trial. There are many more targeted treatments that will undergo trials in FXS, so the future looks bright for new treatments.

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.

Ythdf is a N6-methyladenosine reader that modulates Fmr1 target mRNA selection and restricts axonal growth in Drosophila

N6‐methyladenosine (m⁶A) regulates a variety of physiological processes through modulation of RNA metabolism. This modification is particularly enriched in the nervous system of several species, and its dysregulation has been associated with neurodevelopmental defects and neural dysfunctions. In Drosophila, loss of m⁶A alters fly behavior, albeit the underlying molecular mechanism and the role of m⁶A during nervous system development have remained elusive. Here we find that impairment of the m⁶A pathway leads to axonal overgrowth and misguidance at larval neuromuscular junctions as well as in the adult mushroom bodies. We identify Ythdf as the main m⁶A reader in the nervous system, being required to limit axonal growth. Mechanistically, we show that the m⁶A reader Ythdf directly interacts with Fmr1, the fly homolog of Fragile X mental retardation RNA binding protein (FMRP), to inhibit the translation of key transcripts involved in axonal growth regulation. Altogether, this study demonstrates that the m⁶A pathway controls development of the nervous system and modulates Fmr1 target transcript selection.

Effects of clonidine and methylphenidate on motor activity in Fmr1 knockout mice

Fragile X syndrome (FXS), a disorder caused by a mutation in the FMR1 gene, is often associated with Attention Deficit Hyperactivity Disorder (ADHD). Common treatments for the hyperactivity often seen in ADHD involve the use of stimulants and α2-adrenergic agonists. The Fmr1 knockout (KO) mouse has been found to be a valid model for FXS both biologically and behaviorally. Of particular interest to our research, the Fmr1 KO mouse has been demonstrated to show increased locomotion in comparison to wild type (WT) littermates. In the present study, we assessed the effects of clonidine (0.05 mg/kg) and methylphenidate (5 mg/kg) on motor activity in Fmr1 KO mice and their WT littermates in the open field test. Results showed that methylphenidate increased motor activity in both genotypes. Clonidine decreased motor activity in both genotypes, but the effect was delayed in the Fmr1 KO mice.

Outcome measures for clinical trials in fragile X syndrome

OBJECTIVE

Progress in basic neuroscience has led to identification of molecular targets for treatment in fragile X syndrome (FXS) and other neurodevelopmental disorders; however, there is a gap in translation to targeted therapies in humans. One major obstacle to the demonstration of efficacy in human trials has been the lack of generally accepted endpoints to assess improvement in function in individuals with FXS. To address this problem, the National Institutes of Health convened a meeting of leading scientists and clinicians with the goal of identifying and standardizing outcome measures for use as potential endpoints in clinical trials in FXS.

METHODS

Participants in the meeting included FXS experts, experts in the design and implementation of clinical trials and measure development, and representatives from advocacy groups, industry, and federal agencies.

RESULTS

The group generated recommendations for optimal outcome measures in cognitive, behavioral, and biomarker/medical domains, including additional testing and validation of existing measures and development of new measures in areas of need. Although no one endpoint or set of endpoints could be identified that met all criteria as an optimal measure, recommendations are presented in this report.

CONCLUSION

The report is expected to guide the selection of measures in clinical trials and lead to the use of a more consistent battery of measures across trials. Furthermore, this will help to direct research toward gaps in the development of validated FXS-specific outcome measures and to assist with interpretation of clinical trial data by creating templates for measurement of treatment efficacy.

Hyper-reactivity in fragile X syndrome females: generalised or specific to socially-salient stimuli? A skin conductance study

Fragile X syndrome (FXS) is characterised by hyper-reactivity, autistic tendencies and social anxiety. It has been hypothesised that the FXS social phenotype is secondary to a generalised hyper-reactivity that leads to social avoidance. No study, however, has investigated whether hyperarousal in FXS is generalised or more specific to socially salient information. We recorded skin conductance responses (SCRs) while females with FXS, as well as chronological age-(CA-) and mental age-(MA-) matched controls, viewed two sets of visual images: direct-gaze emotional faces and affectively arousing scenes. Explicit emotion recognition and subjective ratings of emotions aroused by images were also recorded. Overall, females with FXS displayed hyper-reactivity only when viewing the more socially salient stimuli (emotional faces), compared to CA-matched controls, but not MA-matched controls. Moreover, females with FXS also displayed atypical emotion recognition abilities and subjective ratings of their own emotional states. These findings suggest that any hyper-reactivity observed in FXS may be more specific to socially salient stimuli, rather than generalised.

Cardiovascular and behavioral response to auditory stimuli in boys with fragile X syndrome

OBJECTIVE

The aim of this study was to determine whether young boys with fragile X syndrome (FXS) exhibit abnormal physiological or behavioral responses to a moderately intense auditory stimulus, as heightened sensory reactivity is believed to contribute to problem behaviors in this population.

METHODS

We examined the physiological basis, via heart activity, of auditory startle in young boys with FXS (n = 22) compared with typically developing controls (n = 27). Associations with mental age, behavioral reactivity, and chronological age were examined.

RESULTS

Results suggest that older boys with FXS display increased cardiac reactivity to auditory input than younger boys with FXS that distinguishes them from typically developing controls. Higher mental age was associated with decreased latency to react.

CONCLUSIONS

Results contribute to increased understanding of the pathology in sensory processing in boys with FXS, which can inform refinement of the phenotype in young children with FXS and aid in the development of efficacious psychopharmacological and/or behavioral interventions.

Clinic-based retrospective analysis of psychopharmacology for behavior in fragile x syndrome

Fragile X syndrome (FXS) is associated with behavior that limits functioning, including distractibility, hyperactivity, impulsivity, hyperarousal, anxiety, mood dysregulation, and aggression. Medication response and side effect data were reviewed retrospectively for 257 patients (age 14 ± 11 years, range 4–60 years, 203 M, 54 F) attending an FXS clinic. Treatment success rates were defined as the percentage of positive response in the form of documented clinical report of improvement in the behavior(s) being targeted over at least a 6-month period on the medication, without side effects requiring medication discontinuance, while failures were defined as discontinuance of medication due to lack of clinical effectiveness or side effects. Success rate for treatment of targeted behaviors with trials of individual medications was 55% for stimulants, 53% for antidepressants, 62% for alpha2-agonists, and 54% for antipsychotics. With sequential trials of different medications in the same class, success rate improved to 73–77%. Side effect-related failures were highest for antipsychotics. Systematic psychopharmacologic intervention targeted to behavioral symptoms appears helpful in the majority of patients with FXS.

Attention deficit hyperactivity disorder and sensory modulation disorder: a comparison of behavior and physiology

Children with attention deficit hyperactivity disorder (ADHD) are impulsive, inattentive and hyperactive, while children with sensory modulation disorder (SMD), one subtype of Sensory Processing Disorder, have difficulty responding adaptively to daily sensory experiences. ADHD and SMD are often difficult to distinguish. To differentiate these disorders in children, clinical ADHD, SMD, and dual diagnoses were assessed. All groups had significantly more sensory, attention, activity, impulsivity, and emotional difficulties than typical children, but with distinct profiles. Inattention was greater in ADHD compared to SMD. Dual diagnoses had more sensory-related behaviors than ADHD and more attentional difficulties than SMD. SMD had more sensory issues, somatic complaints, anxiety/depression, and difficulty adapting than ADHD. SMD had greater physiological/electrodermal reactivity to sensory stimuli than ADHD and typical controls. Parent-report measures identifying sensory, attentional, hyperactive, and impulsive difficulties varied in agreement with clinician's diagnoses. Evidence suggests ADHD and SMD are distinct diagnoses.

Fragile X syndrome: a psychiatric perspective

Fragile X syndrome (FXS) is associated with a complex but relatively consistent psychiatric phenotype. Recent research has suggested neural substrates for the behavioral abnormalities typically seen in FXS, and enhanced treatment strategies for managing disabling psychiatric comorbidity. While disease-specific, and possibly disease-modifying, therapeutics are being developed for FXS, currently available psychiatric medications can provide significant symptomatic relief of the hyperactivity, anxiety disorders, and affective disturbances often seen in the course of FXS. However, patients with fragile X may be especially susceptible to the psychiatric side effects of these medications, requiring particular care in prescribing. Recent findings concerning disease mechanisms and treatment strategies are reviewed from the perspective of a clinical psychiatrist, in an effort to enhance conventional pharmacotherapy of FXS.

Phenotypes within sensory modulation dysfunction

Sensory modulation disorder (SMD) is a severe inability to regulate responses to everyday sensory stimulation to which most people easily adapt. It is estimated to affect 5% to 16% of the general population of children. Although heterogeneity is seen in the presentation clinically, previous research has not empirically investigated whether the clinical heterogeneity of SMD can be classified into subtypes. This study explores a cohort of 98 children identified with SMD at the Department of Pediatric Rehabilitation by a member of the occupational therapy team at The Children's Hospital of Denver. Two subtypes of SMD were identified through cluster analysis based on data from 4 parent-report instruments. The first subtype is characterized by sensory seeking/craving, hyperactive, impulsive, externalizing (eg, delinquent, aggressive), unsocial, inadaptive, and impaired cognitive/social behavior. The second subtype is characterized by movement sensitivity, emotionally withdrawal, and low energy/weak behavior. Findings from this study present a step toward understanding and classifying the complexities of children with SMDs.

The psychiatric presentation of fragile x: evolution of the diagnosis and treatment of the psychiatric comorbidities of fragile X syndrome

Fragile X syndrome (FXS) is the leading inherited cause of mental retardation and autism spectrum disorders worldwide. It presents with a distinct behavioral phenotype which overlaps significantly with that of autism. Unlike autism and most common psychiatric disorders, the neurobiology of fragile X is relatively well understood. Lack of the fragile X mental retardation protein causes dysregulation of synaptically driven protein synthesis, which in turn causes global disruption of synaptic plasticity. Thus, FXS can be considered a disorder of synaptic plasticity, and a developmental disorder in the purest sense: mutation of the FMR1 (fragile X mental retardation 1) gene results in abnormal synaptic development in response to experience. Accumulation of this abnormal synaptic development, over time, leads to a characteristic and surprisingly consistent behavioral phenotype of attention deficit, hyperactivity, impulsivity, multiple anxiety symptoms, repetitive/perseverative/stereotypic behaviors, unstable affect, aggression, and self-injurious behavior. Many features of the behavioral and psychiatric phenotype of FXS follow a developmental course, waxing and waning over the life span. In most cases, symptoms present as a mixed clinical picture, not fitting established diagnostic categories. There have been many clinical trials in fragile X subjects, but no placebo-controlled trials of adequate size or methodology utilizing the most commonly prescribed psychiatric medications. However, large and well-designed trials of investigational agents which target the underlying pathology of FXS have recently been completed or are under way. While the literature offers little guidance to the clinician treating patients with FXS today, potentially disease-modifying treatments may be available in the near future.

Psychiatric features in children with genetic syndromes: toward functional phenotypes

Neurodevelopmental disorders with identified genetic etiologies present a unique opportunity to study gene-brain-behavior connections in child psychiatry. Parsing complex human behavior into dissociable components is facilitated by examining a relatively homogenous genetic population. As children with developmental delay carry a greater burden of mental illness than the general population, familiarity with the most common genetic disorders will serve practitioners seeing a general child population. In this article, basic genetic testing and 11 of the most common genetic disorders are reviewed, including the evidence base for treatment. Based on their training in child development, family systems, and multimodal treatment, child psychiatrists are well positioned to integrate cognitive, behavioral, social, psychiatric, and physical phenotypes, with a focus on functional impairment.

Treatment effects of stimulant medication in young boys with fragile X syndrome

Fragile X syndrome (FXS) is the most common inherited form of intellectual disability and is caused by a CGG repeat expansion at Xq27.3 on the FMR1 gene. The majority of young boys with FXS display poor attention and hyperactivity that is disproportionate to their cognitive disability, and approximately 70% meet diagnostic criteria for attention-deficit/hyperactivity disorder. Psychopharmacology is employed with 82% of young males 5-17 years of age, with stimulant medication as the most common medication prescribed. This study evaluated the effects of stimulant medication on the academic performance, attention, motor activity, and psychophysiological arousal of boys with FXS, as well as the concordance of effects within individuals. Participants in this study included 12 boys with FXS who were treated with stimulants. Participants completed videotaped academic testing on two consecutive days and were randomly assigned to be off stimulants for 1 day and on stimulants the other day. On each day, multiple measures including academic performance, behavior regulation, and psychophysiological arousal were collected. Approximately 75% of participants performed better on attention and academic measures, and 70% showed improved physiological regulation while on stimulant medication. A high degree of concordance among measures was found. Lower intelligence quotient (IQ), but not age, correlated with greater improvements in in-seat behavior. IQ and age did not relate to on-task behaviors. The frequency and magnitude of response to stimulant medication in boys with FXS is higher than those reported for most children with non-specific intellectual disabilities and autism spectrum disorder.

Autonomic regulation in fragile X syndrome

Autonomic reactivity was studied in individuals with fragile X syndrome (FXS), a genetic disorder partially characterized by abnormal social behavior. Relative to age-matched controls, the FXS group had faster baseline heart rate and lower amplitude respiratory sinus arrhythmia (RSA). In contrast to the typically developing controls, there was a decrease in RSA with age within the FXS group. Moreover, within the FXS group heart rate did not slow with age. The FXS group also responded with an atypical increase in RSA to the social challenge, while the control group reduced RSA. In a subset of the FXS group, the autonomic profile did not change following 2 months and 1 year of lithium treatment. The observed indices of atypical autonomic regulation, consistent with the Polyvagal Theory, may contribute to the deficits in social behavior and social communication observed in FXS.

TMS: using the theta-burst protocol to explore mechanism of plasticity in individuals with Fragile X syndrome and autism

Fragile X Syndrome (FXS), also known as Martin-Bell Syndrome, is a genetic abnormality found on the X chromosome. Individuals suffering from FXS display abnormalities in the expression of FMR1--a protein required for typical, healthy neural development. Recent data has suggested that the loss of this protein can cause the cortex to be hyperexcitable thereby affecting overall patterns of neural plasticity. In addition, Fragile X shows a strong comorbidity with autism: in fact, 30% of children with FXS are diagnosed with autism, and 2-5% of autistic children suffer from FXS. Transcranial Magnetic Stimulation (a non-invasive neurostimulatory and neuromodulatory technique that can transiently or lastingly modulate cortical excitability via the application of localized magnetic field pulses) represents a unique method of exploring plasticity and the manifestations of FXS within affected individuals. More specifically, Theta-Burst Stimulation (TBS), a specific stimulatory protocol shown to modulate cortical plasticity for a duration up to 30 minutes after stimulation cessation in healthy populations, has already proven an efficacious tool in the exploration of abnormal plasticity. Recent studies have shown the effects of TBS last considerably longer in individuals on the autistic spectrum--up to 90 minutes. This extended effect-duration suggests an underlying abnormality in the brain's natural plasticity state in autistic individuals, similar to the hyperexcitability induced by Fragile X Syndrome. In this experiment, utilizing single-pulse motor-evoked potentials (MEPs) as our benchmark, we will explore the effects of both intermittent and continuous TBS on cortical plasticity in individuals suffering from FXS and individuals on the Autistic Spectrum.

Taurine regulation of short term synaptic plasticity in fragile X mice

BACKGROUND

Fragile X Syndrome is the most common known genetic cause of autism. The Fmr1-KO mouse, lacks the fragile X mental retardation protein (FMRP), and is used as a model of the syndrome. The core behavioral deficits of autism may be conceptualized either as excessive adherence to patterns as seen in repetitive actions and aberrant language, or as insensitivity to subtle but socially important changes in patterns. The hippocampus receives information from the entorhinal cortex and plays a crucial role in the processing of patterned information. To gain more insight into the physiological function of FMRP and the neuronal mechanisms underlying fragile X syndrome, we examined the electrophysiological response of the hippocampus to pair pulse stimulation as a measure of patterned information processing and how it is affected in the Fmr1-KO mouse.

METHODS

In this study, we used paired-pulse stimulation of the afferent perforant path and recorded from the CA1 region of the hippocampus. Two-month-old FVB/NJ male mice and age-matched Fmr1-KO mice were used in this study. Hippocampal slices were prepared, equilibrated in artificial cerebrospinal fluid (aCSF), and excitatory post synaptic potentials (EPSPs) measured by stimulating the perforant path of the dentate gyrus (DG) while recording from the molecular layer of CA1. Stimulation occurred by setting current and pulse width to evoke a fixed percentage of maximal EPSP amplitude. This stimulation paradigm allowed us to examine the processing capabilities of the hippocampus as a function of increasing interstimulus intervals (ISI) and how taurine, a GABAA receptor agonist, affects such information processing.

RESULTS

We found that hippocampal slices from wild type (WT) showed pair-pulse facilitation at ISI of 100-300 ms whereas slices from Fmr1-KO brains showed a consistent pair-pulse depression at a comparable ISI. Addition of 10 muM taurine to WT slices resulted in a drastic decrease of the peak response to the second stimulus, resulting in an initial depression at 100 ms ISI followed by potentiation at higher ISI (150 ms and above). In the presence of taurine, the amplitude of the second response remained significantly lower than in its absence. Fmr1-KO mice however, were completely insensitive to taurine application and pair-pulse stimulation always resulted in a depression of the response to the second stimulus.

CONCLUSIONS

Previously we reported that Fmr1-KO mice have reduced beta subunits of the GABAA receptors. We also showed as well as others that taurine acts as an agonist or a modulator for GABAA receptors. Therefore, the insensitivity of Fmr1-KO slices to taurine application could be due to the reduced binding sites on the GABAA receptors in the Fmr1-KO mice.

Fragile X: leading the way for targeted treatments in autism

Two different mutations in the FMR1 gene may lead to autism. The full mutation, with >200 CGG repeats in the 5' end of FMR1, leads to hypermethylation and transcriptional silencing of FMR1, resulting in absence or deficiency of the protein product, FMRP. Deficiency of FMRP in the brain causes fragile X syndrome (FXS). Autism occurs in approximately 30% of those with FXS, and pervasive developmental disorders-not otherwise specified occur in an additional 30%. FMRP is an RNA binding protein that modulates receptor-mediated dendritic translation; deficiency leads to dysregulation of many proteins important for synaptic plasticity. Group I metabotropic glutamate receptor (mGluR1/5) activated translation is upregulated in FXS, and new targeted treatments that act on this system include mGluR5 antagonists and GABA agonists, which may reverse the cognitive and behavioral deficits in FXS. Matrix metalloproteinase 9 (MMP-9) is one of the proteins elevated in FXS, and minocycline reduces excess MMP-9 activity in the Fmr1 knockout mouse model of FXS. Both minocycline and mGluR5 antagonists are currently being evaluated in patients with FXS through controlled treatment trials. The premutation (55-200 CGG repeats) may also contribute to the mechanism of autism in approximately 10% of males and 2-3% of females. Premutations with <150 repeats exert cellular effects through a different molecular mechanism, one that involves elevated levels of FMR1 mRNA, CGG-mediated toxicity to neurons, early cell death, and fragile X-associated tremor/ataxia syndrome. In those with large premutations (150-200), lowered levels of FMRP also occur.

Psychiatric features in children with genetic syndromes: toward functional phenotypes

Neurodevelopmental disorders with identified genetic etiologies present a unique opportunity to study gene-brain-behavior connections in child psychiatry. Parsing complex human behavior into dissociable components is facilitated by examining a relatively homogenous genetic population. As children with developmental delay carry a greater burden of mental illness than the general population, familiarity with the most common genetic disorders will serve practitioners seeing a general child population. In this article basic genetic testing and 11 of the most common genetic disorders are reviewed, including the evidence base for treatment. Based on their training in child development, family systems, and multimodal treatment, child psychiatrists are well positioned to integrate cognitive, behavioral, social, psychiatric, and physical phenotypes, with a focus on functional impairment.

Physiological and behavioral differences in sensory processing: a comparison of children with autism spectrum disorder and sensory modulation disorder

A high incidence of sensory processing difficulties exists in children with Autism Spectrum Disorder (ASD) and children with Sensory Modulation Disorder (SMD). This is the first study to directly compare and contrast these clinical disorders. Sympathetic nervous system markers of arousal and reactivity were utilized in a laboratory paradigm that administered a series of sensory challenges across five sensory domains. The Short Sensory Profile, a standardized parent-report measure, provided a measure of sensory-related behaviors. Physiological arousal and sensory reactivity were lower in children with ASD whereas reactivity after each sensory stimulus was higher in SMD, particularly to the first stimulus in each sensory domain. Both clinical groups had significantly more sensory-related behaviors than typically developing children, with contrasting profiles. The ASD group had more taste/smell sensitivity and sensory under-responsivity while the SMD group had more atypical sensory seeking behavior. This study provides preliminary evidence distinguishing sympathetic nervous system functions and sensory-related behaviors in Autism Spectrum Disorder and Sensory Modulation Disorder. Differentiating the physiology and sensory symptoms in clinical groups is essential to the provision of appropriate interventions.

Advances in the treatment of fragile X syndrome

The FMR1 mutations can cause a variety of disabilities, including cognitive deficits, attention-deficit/hyperactivity disorder, autism, and other socioemotional problems, in individuals with the full mutation form (fragile X syndrome) and distinct difficulties, including primary ovarian insufficiency, neuropathy and the fragile X-associated tremor/ataxia syndrome, in some older premutation carriers. Therefore, multigenerational family involvement is commonly encountered when a proband is identified with a FMR1 mutation. Studies of metabotropic glutamate receptor 5 pathway antagonists in animal models of fragile X syndrome have demonstrated benefits in reducing seizures, improving behavior, and enhancing cognition. Trials of metabotropic glutamate receptor 5 antagonists are beginning with individuals with fragile X syndrome. Targeted treatments, medical and behavioral interventions, genetic counseling, and family supports are reviewed here.

Limbic epileptogenesis in a mouse model of fragile X syndrome

Fragile X syndrome (FXS), caused by silencing of the Fmr1 gene, is the most common form of inherited mental retardation. Epilepsy is reported to occur in 20-25% of individuals with FXS. However, no overall increased excitability has been reported in Fmr1 knockout (KO) mice, except for increased sensitivity to auditory stimulation. Here, we report that kindling increased the expressions of Fmr1 mRNA and protein in the forebrain of wild-type (WT) mice. Kindling development was dramatically accelerated in Fmr1 KO mice, and Fmr1 KO mice also displayed prolonged electrographic seizures during kindling and more severe mossy fiber sprouting after kindling. The accelerated rate of kindling was partially repressed by inhibiting N-methyl-D-aspartic acid receptor (NMDAR) with MK-801 or mGluR5 receptor with 2-methyl-6-(phenylethynyl)-pyridine (MPEP). The rate of kindling development in WT was not effected by MPEP, however, suggesting that FMRP normally suppresses epileptogenic signaling downstream of metabolic glutamate receptors. Our findings reveal that FMRP plays a critical role in suppressing limbic epileptogenesis and predict that the enhanced susceptibility of patients with FXS to epilepsy is a direct consequence of the loss of an important homeostatic factor that mitigates vulnerability to excessive neuronal excitation.

A mouse model of fragile X syndrome exhibits heightened arousal and/or emotion following errors or reversal of contingencies

This study was designed to further assess cognitive and affective functioning in a mouse model of Fragile X syndrome (FXS), the Fmr1(tm1Cgr) or Fmr1 "knockout" (KO) mouse. Male KO mice and wild-type littermate controls were tested on learning set and reversal learning tasks. The KO mice were not impaired in associative learning, transfer of learning, or reversal learning, based on measures of learning rate. Analyses of videotapes of the reversal learning task revealed that both groups of mice exhibited higher levels of activity and wall-climbing during the initial sessions of the task than during the final sessions, a pattern also seen for trials following an error relative to those following a correct response. Notably, the increase in both behavioral measures seen early in the task was significantly more pronounced for the KO mice than for controls, as was the error-induced increase in activity level. This pattern of effects suggests that the KO mice reacted more strongly than controls to the reversal of contingencies and pronounced drop in reinforcement rate, and to errors in general. This pattern of effects is consistent with the heightened emotional reactivity frequently described for humans with FXS.

Diagnostic validity of sensory over-responsivity: a review of the literature and case reports

Atypical responses to sensory stimulation are frequently reported to co-occur with diagnoses such as autism, ADHD, and Fragile-X syndrome. It has also been suggested that children and adults may present with atypical sensory responses while failing to meet the criteria for other medical or psychological diagnoses. This may be particularly true for individuals with over-responsivity to sensation. This article reviews the literature related to sensory over-responsivity and presents three pediatric cases that present a profile of having sensory over-responsivity without a co-occurring diagnosis. Findings from these cases provide very preliminary evidence to support the suggestion that sensory over-responsivity can occur as a sole diagnosis. Within this small group, tactile over-responsivity was the most common and pervasive form of this condition.

Neuroanatomical, molecular genetic, and behavioral correlates of fragile X syndrome

Fragile X syndrome (FXS) is a leading cause of inherited mental retardation. In the vast majority of cases, this X-linked disorder is due to a CGG expansion in the 5' untranslated region of the fmr-1 gene and the resulting decreased expression of its associated protein, FMRP. FXS is characterized by a number of cognitive, behavioral, anatomical, and biological abnormalities. FXS provides a unique opportunity to study the consequence of mutation in a single gene on the development and proper functioning of the CNS. The current focus on the role of FMRP in neuronal maturation makes it timely to assemble the extant information on how reduced expression of the fmr-1 gene leads to neuronal dysmorphology. The purpose of this review is to summarize recent genetic, neuroanatomical, and behavioral studies of fragile X syndrome and to offer potential mechanisms to account for the pleiotropic phenotype of this disorder.

Lessons from fragile X regarding neurobiology, autism, and neurodegeneration

The fragile X mental retardation 1 gene (FMR1) mutation causes two disorders: fragile X syndrome (FXS) in those with the full mutation and the fragile X-associated tremor/ataxia syndrome (FXTAS) in some older individuals with the premutation. FXS is caused by a deficiency of the FMR1 protein (FMRP) leading to dysregulation of many genes that create a phenotype with ADHD, anxiety, and autism. FXTAS is caused by the elevation of FMR1-mRNA to levels 2 to 8 times normal in the premutation. This causes an RNA gain of function toxicity leading to brain atrophy, white matter disease, neuronal and astrocytic inclusion formation, and subsequent ataxia, intention tremor, peripheral neuropathy, and cognitive decline. The neurobiology and pathophysiology of FXS and FXTAS are described in detail.

Emotional task-dependent low-frequency fluctuations and methylphenidate: Wavelet scaling analysis of 1/f-type fluctuations in fMRI of the cerebellar vermis

Ion channel currents, neural firing patterns, and brain BOLD signals display 1/f-type fluctuations or fractal properties in time. By design, fMRI methods attempt to minimize the contribution of variance from low-frequency physiological 1/f-noise. New fMRI methods are described to visualize and measure 1/f-type BOLD fluctuations in volunteers recalling affectively neutral or emotional memories or meditating (i.e., attending to breathing) then retrospectively rating emotional content. A wavelet scaling exponent (alpha) was used to characterize signals from 0.015625 to 0.5Hz in cerebellar lobules VIII to X of the vermis (posterior inferior vermis; PIV), a region coordinating balance, eye tracking, locomotion, and vascular tone, and a possible site of pathology in attention deficit hyperactivity disorder (ADHD).

RESULTS

Changes in alpha and emotional measures were correlated in PIV voxels (r = 0.622, d.f .= 14, P < 0.0005), but not other regions examined. In contrast, conventional means and standard deviations of PIV voxels were unchanged. Methylphenidate, shown to decrease slow oscillations in rodent basal ganglia [Ruskin DN, Bergstrom DA, Shenker A, Freeman LE, Baek D, Walters JR. Drugs used in the treatment of attention-deficit/hyperactivity disorder affect postsynaptic firing rate and oscillation without preferential dopamine autoreceptor action. Biol Psychiatry 2001;49:340-50.], abolished task-dependent alpha changes in the PIV of an adult with ADHD. Wavelet analysis of long BOLD time series appears well suited to fractal physiology and studies of pharmacologically modulated cerebellar-thalamic-cortical function in ADHD or other psychiatric disorders.

A phenotypic and molecular characterization of the fmr1-tm1Cgr Fragile X mouse

Fragile X Syndrome is the most common form of inherited mental retardation. It is also known for having a substantial behavioral morbidity, including autistic features. In humans, Fragile X Syndrome is almost always caused by inactivation of the X-linked FMR1 gene. A single knockout mouse model, fmr1-tm1Cgr, exists. In this report we further characterize the cognitive and behavioral phenotype of the fmr1-tm1Cgr Fragile X mouse through the use of F1 hybrid mice derived from two inbred strains (FVB/NJ and C57BL/6J). Use of F1 hybrids allows focus on the effects of the fmr1-tm1Cgr allele with reduced influence from recessive alleles present in the parental inbred strains. We find that the cognitive phenotype of fmr1-tm1Cgr mice, including measures of working memory and learning set formation that are known to be seriously impacted in humans with Fragile X Syndrome, are essentially normal. Further testing of inbred strains supports this conclusion. Thus, any fmr1-tm1Cgr cognitive deficit is surprisingly mild or absent. There is, however, clear support presented for a robust audiogenic seizure phenotype in all strains tested, as well as increased entries into the center of an open field. Finally, a molecular examination of the fmr1-tm1Cgr mouse shows that, contrary to common belief, it is not a molecular null. Implications of this finding for interpretation of the phenotype are discussed.

Neuropsychiatric symptoms of fragile X syndrome: pathophysiology and pharmacotherapy

Fragile X syndrome is the leading inherited form of mental retardation, and second only to Down's syndrome as a cause of mental retardation attributable to an identifiable genetic abnormality. Fragile X syndrome is caused by a defect in the fragile X mental retardation 1 gene (FMR1), located near the end of the long arm of the X chromosome. FMR1 normally synthesises the fragile X protein (FMRP), but mutations in FMR1 lead to a lack of FMRP synthesis, resulting in fragile X syndrome. While the specific function of FMRP is not yet fully understood, the protein is known to be important for normal brain development. The physical, cognitive and behavioural features of individuals with fragile X syndrome depend on gender (females have two X chromosomes, one active and one inactive) and the molecular status of the mutation (premutation, full mutation or mosaic). Features of the behavioural profile of individuals with fragile X syndrome include hypersensitivity to stimuli, overarousability, inattention, hyperactivity and (mostly in men) explosive and aggressive behaviour to others or self. Social anxiety, other anxiety disorders, depression, impulse control disorder and mood disorders are the most common psychiatric disorders diagnosed in individuals with fragile X syndrome, although no formal studies have been undertaken. There have been very few psychopharmacological studies of the treatment of behaviours associated with fragile X syndrome. These limited studies and surveys of psychotropic drugs used in individuals with fragile X syndrome suggest that stimulants are helpful for hyperactivity, that alpha(2)-adrenoceptor agonists and beta-adrenoceptor antagonists help to control overarousability, impulsivity and aggressiveness, and that SSRIs can control anxiety, impulsivity and irritability, alleviate depressive symptoms and decrease aggressive and self-injurious behaviour. Typical and atypical antipsychotics in combination with other psychotropics have been used for control of psychotic disorders and severe aggressive behaviours. Mood stabilisers have been found to be useful when mood dysregulation or mood disorders are present with or without aggressive behaviour. Folic acid and L-acetylcarnitine (levacecarnine) have not been found to improve deficits or behaviours. As there is no specific psychotropic drug for any of the deficits or behaviours associated with fragile X syndrome, clinicians are advised to diagnose any psychiatric syndromes or disorders present and treat them with the appropriate psychotropic drug. If no psychiatric disorder can be diagnosed and the patient's challenging behaviours cannot be controlled with environmental manipulation or behaviour modification techniques, the most benign psychotropic drug should be used. Antipsychotics should be reserved for psychotic disorders, for impulse control disorders (used in combination with other psychotropics), or when challenging behaviours constitute an emergency. In the future, new medications targeting molecules implicated in the modulation of anxiety, fear and fear responding will be useful for treating the social anxiety and overarousability exhibited by individuals with fragile X syndrome.

Psychopharmacology in fragile X syndrome--present and future

In addition to cognitive disability, fragile X syndrome (FXS) is associated with behavioral problems that are often functionally limiting. There are few controlled trials to guide treatment; however, available information does suggest that medications can be quite helpful for a number of categories of behavioral disturbance in FXS. Specifically, stimulants appear to be quite useful for management of distractibility, hyperactivity, and impulsive behavior; antidepressants help with anxiety, obsessive-compulsive behaviors and mood dysregulation; and antipsychotics can reduce aggression. These medications are supportive and help minimize dysfunctional behaviors and maximize functioning. As more is learned about the neural functions of FMRP, medications in the future will be expected to target specific synaptic mechanisms dysregulated in FXS brain and thus ameliorate the cognitive deficit with resultant behavioral improvements. This article summarizes knowledge about effectiveness and approaches to management of currently available psychopharmacology for behavior in FXS and discusses early leads to future treatments for cognition.

Understanding the biological underpinnings of fragile X syndrome

PURPOSE OF REVIEW

The purpose of this review is to present the latest findings on fragile X syndrome and to put them into perspective. Fragile X syndrome is a relatively common form of inherited mental retardation, caused by loss of function of the FMR1 gene on the long arm of the X chromosome. The molecular mechanisms underlying the syndrome are complex and continue to surprise researchers more than 12 years after the cloning of the gene.

RECENT FINDINGS

We will specifically discuss the various aspects of the clinical phenotype, reassessed with the employment of functional imaging and electrophysiological techniques. The unexpected finding of a pathologic phenotype in premutation carriers is highlighted, as it represents a new and distinct condition with a different presentation in males and females. The third section deals briefly with the various functions of the FMRP protein, an RNA-binding protein interacting with multiple RNA molecules as well as proteins. It is important to realize that FMRP is probably changing partners several times, depending on its localization, on posttranslational modifications and on the available interacting proteins. In the following section, we present in short recent discoveries on the defective neuronal circuits in the fragile X syndrome. Most of these new data were made available by the study of animal models, mostly the Fmr1 knockout mouse, but also Drosophila.

SUMMARY

We briefly discuss the alternative options for treating fragile X syndrome. Presently, a neuropharmacological approach acting on either critical receptors or aimed at reactivating the silenced FMR1 gene appears promising.