The fragile X premutation: into the phenotypic fold

FMRP Associates with Cytoplasmic Granules at the Onset of Meiosis in the Human Oocyte

Germ cell development and primordial follicle formation during fetal life is critical in establishing the pool of oocytes that subsequently determines the reproductive lifespan of women. Fragile X-associated primary ovarian insufficiency (FXPOI) is caused by inheritance of the FMR1 premutation allele and approximately 20% of women with the premutation allele develop ovarian dysfunction and premature ovarian insufficiency. However, the underlying disease mechanism remains obscure, and a potential role of FMRP in human ovarian development has not been explored. We have characterised the expression of FMR1 and FMRP in the human fetal ovary at the time of germ cell entry into meiosis through to primordial follicle formation. FMRP expression is exclusively in germ cells in the human fetal ovary. Increased FMRP expression in germ cells coincides with the loss of pluripotency-associated protein expression, and entry into meiosis is associated with FMRP granulation. In addition, we have uncovered FMRP association with components of P-bodies and stress granules, suggesting it may have a role in mRNA metabolism at the time of onset of meiosis. Therefore, this data support the hypothesis that FMRP plays a role regulating mRNAs during pivotal maturational processes in fetal germ cells, and ovarian dysfunction resulting from FMR1 premutation may have its origins during these stages of oocyte development.

Testing the Feasibility of a Passive and Active Case Ascertainment System for Multiple Rare Conditions Simultaneously: The Experience in Three US States

Background

Owing to their low prevalence, single rare conditions are difficult to monitor through current state passive and active case ascertainment systems. However, such monitoring is important because, as a group, rare conditions have great impact on the health of affected individuals and the well-being of their caregivers. A viable approach could be to conduct passive and active case ascertainment of several rare conditions simultaneously. This is a report about the feasibility of such an approach.

Objective

To test the feasibility of a case ascertainment system with passive and active components aimed at monitoring 3 rare conditions simultaneously in 3 states of the United States (Colorado, Kansas, and South Carolina). The 3 conditions are spina bifida, muscular dystrophy, and fragile X syndrome.

Methods

Teams from each state evaluated the possibility of using current or modified versions of their local passive and active case ascertainment systems and datasets to monitor the 3 conditions. Together, these teams established the case definitions and selected the variables and the abstraction tools for the active case ascertainment approach. After testing the ability of their local passive and active case ascertainment system to capture all 3 conditions, the next steps were to report the number of cases detected actively and passively for each condition, to list the local barriers against the combined passive and active case ascertainment system, and to describe the experiences in trying to overcome these barriers.

Results

During the test period, the team from South Carolina was able to collect data on all 3 conditions simultaneously for all ages. The Colorado team was also able to collect data on all 3 conditions but, because of age restrictions in its passive and active case ascertainment system, it was able to report few cases of fragile X syndrome. The team from Kansas was able to collect data only on spina bifida. For all states, the implementation of an active component of the ascertainment system was problematic. The passive component appears viable with minor modifications.

Conclusions

Despite evident barriers, the joint passive and active case ascertainment of rare disorders using modified existing surveillance systems and datasets seems feasible, especially for systems that rely on passive case ascertainment.

Autism Symptoms Across Adulthood in Men with Fragile X Syndrome: A Cross-Sectional Analysis

A cross-sectional analysis was used to examine age-related differences in ASD symptoms and corresponding differences in disruptive behavior and social skills in 281 adult men with fragile X syndrome. Four age groups were created: 18-21, 22-29, 30-39, and 40-49 years. The 18-21 year-old group was reported to have more impairments in verbal communication than the 22-29 year-old group and more restricted and repetitive behaviors than the 40-49 year-old group. There was not an age-group difference in the percentage of men who met criteria for an ASD diagnosis based on respondent-reported, current symptoms. There was a trend for an age-related difference in disruptive behavior. Findings add to understanding of the developmental trajectory of ASD symptoms in adulthood.

Eyeblink conditioning: a non-invasive biomarker for neurodevelopmental disorders

Eyeblink conditioning (EBC) is a classical conditioning paradigm typically used to study the underlying neural processes of learning and memory. EBC has a well-defined neural circuitry, is non-invasive, and can be employed in human infants shortly after birth making it an ideal tool to use in both developing and special populations. In addition, abnormalities in the cerebellum, a region of the brain highly involved in EBC, have been implicated in a number of neurodevelopmental disorders including autism spectrum disorders (ASDs). In the current paper, we review studies that have employed EBC as a biomarker for several neurodevelopmental disorders including fetal alcohol syndrome, Down syndrome, fragile X syndrome, attention deficit/hyperactivity disorder, dyslexia, specific language impairment, and schizophrenia. In addition, we discuss the benefits of using such a tool in individuals with ASD.

Placebo Responses in Genetically Determined Intellectual Disability: A Meta-Analysis

Background

Genetically determined Intellectual Disability (ID) is an intractable condition that involves severe impairment of mental abilities such as learning, reasoning and predicting the future. As of today, little is known about the placebo response in patients with ID.

Objective

To determine if placebo response exists in patients with genetically determined ID.

Data sources and Study selection

We searched Medline/PubMed, EMBASE, CENTRAL and PsycINFO to find all placebo-controlled double-blind randomized clinical trials (RCTs) in patients with genetically determined ID, published up to April 2013, focusing on core ID symptoms.

Data extraction and synthesis

Two investigators extracted outcome data independently.

Main outcomes and measures

Bias-corrected standardized mean difference (Hedge’s g) was computed for each outcome measure, using the Comprehensive Meta-Analysis software. A priori defined patient sub-groups were analyzed using a mixed-effect model. The relationship between pre-defined continuous variable moderators (age, IQ, year of publication and trial duration) and effect size was analyzed using meta-regression

Results

Twenty-two placebo-controlled double-blind RCTs met the inclusion criteria (n = 721, mean age = 17.1 years, 62% men, mean trial duration = 35 weeks). There was a significant overall placebo response from pre- to post-treatment in patients with ID (g = 0.468, p = 0.002), both for “subjective outcomes” (a third-person’s evaluation of the patient) (g = 0.563, p = 0.022) and “objective outcomes” (direct evaluation of the patient’s abilities) (g = 0.434, p = 0.036). Individuals with higher IQ had higher response to placebo (p = 0.02) and no placebo response was observed in ID patients with comorbid dementia. A significant effect of age (p = 0.02) was found, indicating higher placebo responses in treatment of younger patients.

Conclusions and relevance

Results suggest that patients with genetically determined ID improve in the placebo arm of RCTs. Several mechanisms may contribute to placebo effects in ID, including expectancy, implicit learning and “placebo-by-proxy” induced by clinicians/family members. As the condition is refractory, there is little risk that improvements are explained by spontaneous remission. While new avenues for treatment of genetically determined ID are emerging, our results demonstrate how contextual factors can affect clinical outcomes and emphasize the importance of being vigilant on the role of placebos when testing novel treatments in ID.

Distribution of fragile X mental retardation 1 CGG repeat and flanking haplotypes in a large Chinese population

Fragile X syndrome is mainly caused by a CGG repeat expansion within the 5' UTR of the fragile X mental retardation 1 (FMR1) gene. Previous analyses of the FMR1 CGG repeat patterns and flanking haplotypes in Caucasians and African Americans have identified several factors that may influence repeat instability. However, the CGG repeat patterns and distribution for FRAXAC2 have not yet been investigated in mainland Chinese. We surveyed the CGG repeat lengths in 1113 Han Chinese (534 males and 579 females), and the CGG repeat patterns of 534 males were determined by sequence analysis. We also explored the flanking haplotypes (DXS548-FRAXAC1-FRAXAC2) in 566 unaffected and 28 unrelated fragile X Chinese males. The most frequent alleles for DXS548 and FRAXAC1 were identical between our Chinese population and other Asian populations. We identified several low-abundance alleles for DXS548 and FRAXAC1 not found in previous studies in mainland Chinese and Taiwanese cohorts. The most frequent allele was (CGG)29 followed by (CGG)30, and the most frequent patterns were 9 + 9 + 9, 10 + 9 + 9, and 9 + 9 + 6 + 9, similar to those in Singaporeans. We identified only one premutation female carrier with 89 CGG repeats in the 1113 Han Chinese. A few associations between the CGG repeat patterns and flanking haplotypes were determined in this study. In general, the Chinese population had a smaller number of alleles and lower expected heterozygosity for all three STR markers and FRAXA locus when compared with Caucasians and African Americans. We identified a novel haplotype 7-3-5 + that is significantly associated with the full mutation.

Small-molecule screening using Drosophila models of human neurological disorders

Within the last decade, Drosophila has emerged as a premiere model system for the study of human neurodegenerative diseases, due to the realization that flies and humans share many structurally and functionally related gene families. Development of such disease models in the fly allows genetic approaches to be applied to address specific hypotheses concerning disease progression and to test candidate modifier genes. More recently these fly models have also been used for drug discovery. Here, we describe how to utilize the existing fruit fly models of human neurological disorders to identify small-molecule leads that could potentially be further developed for therapeutic use.

Dietary supplementation of omega-3 fatty acids rescues fragile X phenotypes in Fmr1-Ko mice

Omega-3 polyunsaturated fatty acids (n-3 PUFAs) are known to critically influence brain development and functions. Dietary supplementation with n-3 PUFAs has been suggested as a non-pharmacological therapy for a number of developmental disorders, e.g., autistic spectrum disorders (ASD), but human studies so far have led to conflicting results. Furthermore, it has been hypothesized that the therapeutic impact of n-3 PUFAs on these disorders might be explained by their anti-inflammatory properties and their promoting effects on synaptic function and plasticity, but no clear evidence has been produced in this direction. We evaluated the impact of n-3 PUFA dietary supplementation in a mouse model of fragile X syndrome (FXS), i.e., a major developmental disease and the most frequent monogenic cause of ASD. Fmr1-KO and wild-type mice were provided with a diet enriched or not with n-3 PUFAs from weaning until adulthood when they were tested for multiple FXS-like behaviors. The brain expression of several cytokines and of brain-derived neurotrophic factor (BDNF) was concomitantly assessed as inflammatory and synaptic markers. n-3 PUFA supplementation rescued most of the behavioral abnormalities displayed by Fmr1-KO mice, including alterations in emotionality, social interaction and non-spatial memory, although not their deficits in social recognition and spatial memory. n-3 PUFAs also rescued most of the neuroinflammatory imbalances of KOs, but had a limited impact on their BDNF deficits. These results demonstrate that n-3 PUFAs dietary supplementation, although not a panacea, has a considerable therapeutic value for FXS and potentially for ASD, suggesting a major mediating role of neuroinflammatory mechanisms.

RNA-binding proteins as molecular links between cancer and neurodegeneration

For many years, epidemiological studies have suggested an association between cancer and neurodegenerative disorders-two disease processes that seemingly have little in common. Although these two disease processes share disruptions in a wide range of cellular pathways, including cell survival, cell death and the cell cycle, the end result is very divergent: uncontrolled cell survival and proliferation in cancer and progressive neuronal cell death in neurodegeneration. Despite the clinical data connecting these two disease processes, little is known about the molecular links between them. Among the mechanisms affected in cancer and neurodegenerative diseases, alterations in RNA metabolism are obtaining significant attention given the critical role for RNA transcription, maturation, transport, stability, degradation and translation in normal cellular function. RNA-binding proteins (RBPs) are integral to each stage of RNA metabolism through their participation in the formation of ribonucleoprotein complexes (RNPs). RBPs have a broad range of functions including posttranscriptional regulation of mRNA stability, splicing, editing and translation, mRNA export and localization, mRNA polyadenylation and miRNA biogenesis, ultimately impacting the expression of every single gene in the cell. In this review, we examine the evidence for RBPs as being key a molecular linkages between cancer and neurodegeneration.

The contribution of inhibitory interneurons to circuit dysfunction in Fragile X Syndrome

Many neurological disorders, including neurodevelopmental disorders, report hypersynchrony of neuronal networks. These alterations in neuronal synchronization suggest a link to the function of inhibitory interneurons. In Fragile X Syndrome (FXS), it has been reported that altered synchronization may underlie hyperexcitability, cognitive dysfunction and provide a link to the increased incidence of epileptic seizures. Therefore, understanding the roles of inhibitory interneurons and how they control neuronal networks is of great importance in studying neurodevelopmental disorders such as FXS. Here, we present a review of how interneuron populations and inhibition are important contributors to the loss of excitatory/inhibitory balance seen in hypersynchronous and hyperexcitable networks from neurodevelopmental disorders, and specifically in FXS.

Mouse models of the fragile X premutation and fragile X-associated tremor/ataxia syndrome

Carriers of the fragile X premutation (FPM) have CGG trinucleotide repeat expansions of between 55 and 200 in the 5'-UTR of FMR1, compared to a CGG repeat length of between 5 and 54 for the general population. Carriers were once thought to be without symptoms, but it is now recognized that they can develop a variety of early neurological symptoms as well as being at risk for developing the late onset neurodegenerative disorder fragile X-associated tremor/ataxia syndrome (FXTAS). Several mouse models have contributed to our understanding of FPM and FXTAS, and findings from studies using these models are summarized here. This review also discusses how this information is improving our understanding of the molecular and cellular abnormalities that contribute to neurobehavioral features seen in some FPM carriers and in patients with FXTAS. Mouse models show much of the pathology seen in FPM carriers and in individuals with FXTAS, including the presence of elevated levels of Fmr1 mRNA, decreased levels of fragile X mental retardation protein, and ubiquitin-positive intranuclear inclusions. Abnormalities in dendritic spine morphology in several brain regions are associated with neurocognitive deficits in spatial and temporal memory processes, impaired motor performance, and altered anxiety. In vitro studies have identified altered dendritic and synaptic architecture associated with abnormal Ca(2+) dynamics and electrical network activity. FPM mice have been particularly useful in understanding the roles of Fmr1 mRNA, fragile X mental retardation protein, and translation of a potentially toxic polyglycine peptide in pathology. Finally, the potential for using these and emerging mouse models for preclinical development of therapies to improve neurological function in FXTAS is considered.

Association between macroorchidism and intelligence in FMR1 premutation carriers

Characteristics of fragile X syndrome include macroorchidism and intellectual disability, which are associated with decreased FMRP levels. FMRP is highly expressed in many tissues, but primarily in the brain and testis. The relationship between these two characteristics has not previously been studied in the premutation or carrier state. To examine this among premutation carriers and a possible association with IQ, we evaluated macroorchidism status among 213 males including 142 premutation carriers and 71 controls. The prevalence of macroorchidism among premutation carriers was 32.4% (46 out of 142), and 5.6% among controls (4 out of 71, P < 0.0001). Among premutation carriers, the age-adjusted odds ratio (OR) of macroorchidism was significantly increased with increasing FMR1 mRNA (OR 1.84, 95% confidence interval [CI] 1.04-3.25; P = 0.035). With respect to the association between macroorchidism and IQ, after adjustment for number of CGG repeats and age, premutation carriers with macroorchidism had lower verbal IQ (104.67 ± 15.86, P = 0.0152) and full scale IQ (102.98 ± 15.78, P = 0.0227) than premutation carriers without macroorchidism (verbal IQ 112.38 ± 14.14, full scale IQ 110.24 ± 14.21). Similar associations were observed for both verbal IQ (P = 0.034) and full scale IQ (P = 0.039) after being adjusted for age and FMR1 mRNA. These preliminary data support a correlation between macroorchidism and lower verbal and full scale IQ in a relevant proportion of premutation carrier males. Whether this is due to higher levels of FMR1 mRNA or to lower FMRP levels it remains to be established.

Neurodevelopmental disabilities in children with intermediate and premutation range fragile X cytosine-guanine-guanine expansions

To determine the range of neurodevelopmental diagnoses associated with intermediate (45-54 repeats) and premutation (55-200 repeats) range cytosine-guanine-guanine fragile X expansions, the medical records of children with intermediate or premutation range expansions were retrospectively reviewed, and all neurodevelopmental diagnoses were abstracted. Twenty-nine children (9 female, 20 male; age, 13 months to 17 years) with intermediate (n = 25) or premutation (n = 4) range expansions were identified with neurodevelopmental diagnoses, including global developmental delay/intellectual disability (n = 15), language and learning disorders (n = 9), attention-deficit hyperactivity disorder (n = 5), epilepsy (n = 5), and motor disorders (n = 12), including 2 boys younger than 4 years of age with tremor and ataxia. Thus, children with intermediate or premutation range fragile X cytosine-guanine-guanine expansions may be more susceptible than children without such expansions to other processes, both genetic and environmental, that contribute to neurodevelopmental disability.

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.

Emerging links between homeostatic synaptic plasticity and neurological disease

Homeostatic signaling systems are ubiquitous forms of biological regulation, having been studied for hundreds of years in the context of diverse physiological processes including body temperature and osmotic balance. However, only recently has this concept been brought to the study of excitatory and inhibitory electrical activity that the nervous system uses to establish and maintain stable communication. Synapses are a primary target of neuronal regulation with a variety of studies over the past 15 years demonstrating that these cellular junctions are under bidirectional homeostatic control. Recent work from an array of diverse systems and approaches has revealed exciting new links between homeostatic synaptic plasticity and a variety of seemingly disparate neurological and psychiatric diseases. These include autism spectrum disorders, intellectual disabilities, schizophrenia, and Fragile X Syndrome. Although the molecular mechanisms through which defective homeostatic signaling may lead to disease pathogenesis remain unclear, rapid progress is likely to be made in the coming years using a powerful combination of genetic, imaging, electrophysiological, and next generation sequencing approaches. Importantly, understanding homeostatic synaptic plasticity at a cellular and molecular level may lead to developments in new therapeutic innovations to treat these diseases. In this review we will examine recent studies that demonstrate homeostatic control of postsynaptic protein translation, retrograde signaling, and presynaptic function that may contribute to the etiology of complex neurological and psychiatric diseases.

The role of genetics in the establishment and maintenance of the epigenome

Epigenetic mechanisms play an important role in gene regulation during development. DNA methylation, which is probably the most important and best-studied epigenetic mechanism, can be abnormally regulated in common pathologies, but the origin of altered DNA methylation remains unknown. Recent research suggests that these epigenetic alterations could depend, at least in part, on genetic mutations or polymorphisms in DNA methyltransferases and certain genes encoding enzymes of the one-carbon metabolism pathway. Indeed, the de novo methyltransferase 3B (DNMT3B) has been recently found to be mutated in several types of cancer and in the immunodeficiency, centromeric region instability and facial anomalies syndrome (ICF), in which these mutations could be related to the loss of global DNA methylation. In addition, mutations in glycine-N-methyltransferase (GNMT) could be associated with a higher risk of hepatocellular carcinoma and liver disease due to an unbalanced S-adenosylmethionine (SAM)/S-adenosylhomocysteine (SAH) ratio, which leads to aberrant methylation reactions. Also, genetic variants of chromatin remodeling proteins and histone tail modifiers are involved in genetic disorders like α thalassemia X-linked mental retardation syndrome, CHARGE syndrome, Cockayne syndrome, Rett syndrome, systemic lupus erythematous, Rubinstein-Taybi syndrome, Coffin-Lowry syndrome, Sotos syndrome, and facioescapulohumeral syndrome, among others. Here, we review the potential genetic alterations with a possible role on epigenetic factors and discuss their contribution to human disease.

Carriers of the fragile X mental retardation 1 (FMR1) premutation allele present with increased levels of cytokine IL-10

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is an inherited late-onset neurodegenerative disorder, characterized both by neurological and cognitive deficits. It is caused by the expansion of CGG repeats (55 to 200 repeats) in the noncoding region of the fragile X mental retardation 1 (FMR1) gene. Abnormal immunological patterns are often associated with neurodegenerative disorders and implicated in their etiology. We therefore investigated the immune status of FXTAS patients, which had not been assessed prior to this study.

METHOD

Peripheral blood mononuclear cells (PBMCs) were collected from 15 asymptomatic FMR1 premutation carriers and 20 age-matched controls. Concentrations of three cytokines (IL-6, IL-8, IL-10) were measured in PBMC supernatants using ELISA assays.

RESULTS

We found a significant increase in the concentration of the major anti-inflammatory cytokine IL-10 in supernatants of PBMCs derived from premutation carriers, when compared with controls (P = 0.019). This increase correlated significantly with the number of CGG repeats (P = 0.002).

CONCLUSIONS

Elevated IL-10 levels were observed in all premutation carriers, before appearance of the classical neurological symptoms; therefore, IL-10 may be one of the early biomarkers of FXTAS.

Therapeutic potential of metabotropic glutamate receptor modulators

Glutamate is the main excitatory neurotransmitter in the central nervous system (CNS) and is a major player in complex brain functions. Glutamatergic transmission is primarily mediated by ionotropic glutamate receptors, which include NMDA, AMPA and kainate receptors. However, glutamate exerts modulatory actions through a family of metabotropic G-protein-coupled glutamate receptors (mGluRs). Dysfunctions of glutamatergic neurotransmission have been implicated in the etiology of several diseases. Therefore, pharmacological modulation of ionotropic glutamate receptors has been widely investigated as a potential therapeutic strategy for the treatment of several disorders associated with glutamatergic dysfunction. However, blockade of ionotropic glutamate receptors might be accompanied by severe side effects due to their vital role in many important physiological functions. A different strategy aimed at pharmacologically interfering with mGluR function has recently gained interest. Many subtype selective agonists and antagonists have been identified and widely used in preclinical studies as an attempt to elucidate the role of specific mGluRs subtypes in glutamatergic transmission. These studies have allowed linkage between specific subtypes and various physiological functions and more importantly to pathological states. This article reviews the currently available knowledge regarding the therapeutic potential of targeting mGluRs in the treatment of several CNS disorders, including schizophrenia, addiction, major depressive disorder and anxiety, Fragile X Syndrome, Parkinson’s disease, Alzheimer’s disease and pain.

Fragile X premutation RNA is sufficient to cause primary ovarian insufficiency in mice

Spontaneous 46,XX primary ovarian insufficiency (POI), also known as 'premature menopause' or 'premature ovarian failure', refers to ovarian dysfunction that results in a range of abnormalities, from infertility to early menopause as the end stage. The most common known genetic cause of POI is the expansion of a CGG repeat to 55-199 copies (premutation) in the 5' untranslated region in the X-linked fragile X mental retardation 1 (FMR1) gene. POI associated with the FMR1 premutation is referred to as fragile X-associated POI (FXPOI). Here, we characterize a mouse model carrying the human FMR1 premutation allele and show that FMR1 premutation RNA can cause a reduction in the number of growing follicles in ovaries and is sufficient to impair female fertility. Alterations in selective serum hormone levels, including FSH, LH and 17β-estradiol, are seen in this mouse model, which mimics findings in humans. In addition, we also find that LH-induced ovulation-related gene expression is specifically altered. Finally, we show that the FMR1 premutation allele can lead to reduced phosphorylation of Akt and mTOR proteins. These results together suggest that FMR1 premutation RNA could cause the POI associated with FMR1 premutation carriers, and the Akt/mTOR pathway may serve as a therapeutic target for FXPOI.

Prevalence of CGG expansions of the FMR1 gene in a US population-based sample

The primary goal of this study was to calculate the prevalence of the premutation of the FMR1 gene and of the "gray zone" using a population-based sample of older adults in Wisconsin (n = 6,747 samples screened). Compared with past research, prevalence was relatively high (1 in 151 females and 1 in 468 males for the premutation and 1 in 35 females and 1 in 42 males for the gray zone as defined by 45-54 CGG repeats). A secondary study goal was to describe characteristics of individuals found to have the premutation (n = 30, 7 males and 23 females). We found that premutation carriers had a significantly higher rate of divorce than controls, as well as higher rates of symptoms that might be indicative of fragile X-associated tremor ataxia syndrome (FXTAS; numbness, dizziness/faintness) and fragile X primary ovarian insufficiency (FXPOI; age at last menstrual period). Although not statistically significant, premutation carriers were twice as likely to have a child with disability.

MicroRNA-277 modulates the neurodegeneration caused by Fragile X premutation rCGG repeats

Fragile X-associated tremor/ataxia syndrome (FXTAS), a late-onset neurodegenerative disorder, has been recognized in older male fragile X premutation carriers and is uncoupled from fragile X syndrome. Using a Drosophila model of FXTAS, we previously showed that transcribed premutation repeats alone are sufficient to cause neurodegeneration. MiRNAs are sequence-specific regulators of post-transcriptional gene expression. To determine the role of miRNAs in rCGG repeat-mediated neurodegeneration, we profiled miRNA expression and identified selective miRNAs, including miR-277, that are altered specifically in Drosophila brains expressing rCGG repeats. We tested their genetic interactions with rCGG repeats and found that miR-277 can modulate rCGG repeat-mediated neurodegeneration. Furthermore, we identified Drep-2 and Vimar as functional targets of miR-277 that could modulate rCGG repeat-mediated neurodegeneration. Finally, we found that hnRNP A2/B1, an rCGG repeat-binding protein, can directly regulate the expression of miR-277. These results suggest that sequestration of specific rCGG repeat-binding proteins could lead to aberrant expression of selective miRNAs, which may modulate the pathogenesis of FXTAS by post-transcriptionally regulating the expression of specific mRNAs involved in FXTAS.

Fragile X–associated tremor/ataxia syndrome (FXTAS) is an adult-onset neurodegenerative disorder, usually affecting males over 50 years of age. FXTAS patients are the carriers of fragile X premutation alleles. Using a FXTAS Drosophila model, we previously demonstrated that fragile X premutation rCGG repeats alone could cause neurodegeneration. Pur α and hnRNP A2/B1 were identified as specific premutation rCGG repeat-binding proteins (RBPs) that could bind and modulate fragile X permutation rCGG-mediated neuronal degeneration. MiRNAs are sequence-specific regulators of post-transcriptional gene expression. Here we show that fragile X premutation rCGG repeats could lead to aberrant expression of selective miRNAs, which may modulate the pathogenesis of FXTAS by post-transcriptionally regulating the expression of specific mRNAs involved in FXTAS.

De novo microduplication of the FMR1 gene in a patient with developmental delay, epilepsy and hyperactivity

Loss-of-function due to expansion of a CGG repeat located in the 5'UTR of the FMR1 gene is the most frequent cause of fragile X syndrome. Less than 1% of individuals with fragile X syndrome have been reported to have a partial or full deletion or point mutation of the FMR1 gene. However, whether a copy number gain of the FMR1 gene could result in certain clinical phenotypes has not been fully investigated. Here, we report the case of a child who presented with developmental delay starting at 9 months of age, fine motor and speech delay, progressive seizures since 18 months of age and hyperactivity. Molecular workup identified a de novo microduplication in the Xq27.3 region, including the FMR1 gene and the ASFMR1 gene. The expression level of the FMR1 gene in peripheral blood did not differ from that of the controls. In addition, an inherited 363-kb duplication on the chromosome 1q44 region and an inherited deletion of 168 kb on the chromosome 4p15.31 region were detected. It is not clear whether these inherited copy number variations (CNVs) also have a modifying role in the clinical phenotype of this patient.

Self-injurious behaviour in intellectual disability syndromes: evidence for aberrant pain signalling as a contributing factor

BACKGROUND

In most individuals, injury results in activation of peripheral nociceptors (pain-sensing neurons of the peripheral nervous system) and amplification of central nervous system (CNS) pain pathways that serve as a disincentive to continue harmful behaviour; however, this may not be the case in some developmental disorders that cause intellectual disability (ID). Moreover, individuals affected by ID disorders may initiate self-injurious behaviour to address irritating or painful sensations. In normal individuals, a negative feedback loop decreases sensation of pain, which involves descending inhibitory neurons in the CNS that attenuate spinal nociceptive processing. If spinal nociceptive signalling is impaired in these developmental disorders, an exaggerated painful stimulus may be required in order to engage descending anti-nociceptive signals.

METHODS

Using electronic databases, we conducted a review of publications regarding the incidence of chronic pain or altered pain sensation in ID patients or corresponding preclinical models.

RESULTS

There is a body of evidence indicating that individuals with fragile X mental retardation and/or Rett syndrome have altered pain sensation. These findings in humans are supported by mechanistic studies using genetically modified mice harbouring mutations consistent with the human disease. Thus, once self-injurious behaviour is initiated, the signal to stop may be missing. Several developmental disorders that cause ID are associated with increased incidence of gastroesophageal reflux disease (GERD), which can cause severe visceral pain. Individuals affected by these disorders who also have GERD may self-injure as a mechanism to engage descending inhibitory circuits to quell visceral pain. In keeping with this hypothesis, pharmacological treatment of GERD has been shown to be effective for reducing self-injurious behaviour in some patients. Hence, multiple lines of evidence suggest aberrant nociceptive processing in developmental disorders that cause ID.

CONCLUSIONS

There is evidence that pain pathways and pain amplification mechanisms are altered in several preclinical models of developmental disorders that cause ID. We present hypotheses regarding how impaired pain pathways or chronic pain might contribute to self-injurious behaviour. Studies evaluating the relationship between pain and self-injurious behaviour will provide better understanding of the mechanisms underlying self-injurious behaviour in the ID population and may lead to more effective treatments.

Investigation of amygdala volume in men with the fragile X premutation

Premutation fragile X carriers have a CGG repeat expansion (55 to 200 repeats) in the promoter region of the fragile X mental retardation 1 (FMR1) gene. Amygdala dysfunction has been observed in premutation symptomatology, and recent research has suggested the amygdala as an area susceptible to the molecular effects of the premutation. The current study utilizes structural magnetic resonance imaging (MRI) to examine the relationship between amygdala volume, CGG expansion size, FMR1 mRNA, and psychological symptoms in male premutation carriers without FXTAS compared with age and IQ matched controls. No significant between group differences in amygdala volume were found. However, a significant negative correlation between amygdala volume and CGG was found in the lower range of CGG repeat expansions, but not in the higher range of CGG repeat expansions.

Altered mTOR signaling and enhanced CYFIP2 expression levels in subjects with fragile X syndrome

Fragile X syndrome (FXS) is the most common form of inherited intellectual disability and autism. The protein (FMRP) encoded by the fragile X mental retardation gene (FMR1), is an RNA-binding protein linked to translational control. Recently, in the Fmr1 knockout mouse model of FXS, dysregulated translation initiation signaling was observed. To investigate whether an altered signaling was also a feature of subjects with FXS compared to typical developing controls, we isolated total RNA and translational control proteins from lymphocytes of subjects from both groups (38 FXS and 14 TD). Although we did not observe any difference in the expression level of messenger RNAs (mRNAs) for translational initiation control proteins isolated from participant with FXS, we found increased phosphorylation of the mammalian target of rapamycin (mTOR) substrate, p70 ribosomal subunit 6 kinase1 (S6K1) and of the mTOR regulator, the serine/threonine protein kinase (Akt), in their protein lysates. In addition, we observed increased phosphorylation of the cap binding protein eukaryotic initiation factor 4E (eIF4E) suggesting that protein synthesis is upregulated in FXS. Similar to the findings in lymphocytes, we observed increased phosphorylation of S6K1 in brain tissue from patients with FXS (n = 4) compared to normal age-matched controls (n = 4). Finally, we detected increased expression of the cytoplasmic FMR1-interacting protein 2 (CYFIP2), a known FMRP interactor. This data verify and extend previous findings using lymphocytes for studies of neuropsychiatric disorders and provide evidence that misregulation of mTOR signaling observed in the FXS mouse model also occurs in human FXS and may provide useful biomarkers for designing targeted treatments in FXS.

Chemical screen reveals small molecules suppressing fragile X premutation rCGG repeat-mediated neurodegeneration in Drosophila

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a progressive neurodegenerative disorder recognized in fragile X premutation carriers. Using Drosophila, we previously identified elongated non-coding CGG repeats in FMR1 allele as the pathogenic cause of FXTAS. Here, we use this same FXTAS Drosophila model to conduct a chemical screen that reveals small molecules that can ameliorate the toxic effects of fragile X premutation ribo-CGG (rCGG) repeats, among them several known phospholipase A(2) (PLA(2)) inhibitors. We show that specific inhibition of PLA(2) activity could mitigate the neuronal deficits caused by fragile X premutation rCGG repeats, including lethality and locomotion deficits. Furthermore, through a genetic screen, we identified a PLA(2) Drosophila ortholog that specifically modulates rCGG repeat-mediated neuronal toxicity. Our results demonstrate the utility of Drosophila models for unbiased small molecule screens and point to PLA(2) as a possible therapeutic target to treat FXTAS.

Fragile X mental retardation protein (FMRP) and the spinal sensory system

The purpose of this chapter is to discuss the role of the fragile X mental retardation protein (FMRP) in the spinal sensory system and the potential for use of the mouse model of fragile X syndrome to better understand some aspects of the human syndrome as well as advance knowledge in other areas of investigation, such as pain amplification, an important aspect of clinical pain disorders. We describe how the Fmr1 knockout mouse can be used to better understand the role of Fmrp in axons using cultures of sensory neurons and using manipulations to these neurons in vivo. We also discuss the established evidence for a role of Fmrp in nociceptive sensitization and how this evidence relates to an emerging role of translation control as a key process in pain amplification. Finally, we explore opportunities centered on the Fmr1 KO mouse for gaining further insight into the role of translation control in pain amplification and how this model may be used to identify novel therapeutic targets. We conclude that the study of the spinal sensory system in the Fmr1 KO mouse presents several unique prospects for gaining better insight into the human disorder and other clinical issues, such as chronic pain disorders, that affect millions of people worldwide.

Fragile x syndrome

Recent data from a national survey highlighted a significant difference in obesity rates in young fragile X males (31%) compared to age matched controls (18%). Fragile X syndrome (FXS) is the most common cause of intellectual disability in males and the most common single gene cause of autism. This X-linked disorder is caused by an expansion of a trinucleotide CGG repeat (>200) on the promotor region of the fragile X mental retardation 1 gene (FMR1). As a result, the promotor region often becomes methylated which leads to a deficiency or absence of the FMR1 protein (FMRP). Common characteristics of FXS include mild to severe cognitive impairments in males but less severe cognitive impairment in females. Physical features of FXS include an elongated face, prominent ears, and post-pubertal macroorchidism. Severe obesity in full mutation males is often associated with the Prader-Willi phenotype (PWP) which includes hyperphagia, lack of satiation after meals, and hypogonadism or delayed puberty; however, there is no deletion at 15q11-q13 nor uniparental maternal disomy. Herein, we discuss the molecular mechanisms leading to FXS and the Prader-Willi phenotype with an emphasis on mouse FMR1 knockout studies that have shown the reversal of weight increase through mGluR antagonists. Finally, we review the current medications used in treatment of FXS including the atypical antipsychotics that can lead to weight gain and the research regarding the use of targeted treatments in FXS that will hopefully have a significantly beneficial effect on cognition and behavior without weight gain.

Cognition and lobar morphology in full mutation boys with fragile X syndrome

The aims of the present study are twofold: (1) to examine cortical morphology (CM) associated with alterations in cognition in fragile X syndrome (FXS); (2) to characterize the CM profile of FXS versus FXS with an autism diagnosis (FXS+Aut) as a preliminary attempt to further elucidate the behavioral distinctions between the two sub-groups. We used anatomical magnetic resonance imaging surface-based morphometry in 21 male children (FXS N=11 and age [2.27-13.3] matched controls [C] N=10). We found (1) increased whole hemispheric and lobar cortical volume, cortical thickness and cortical complexity bilaterally, yet insignificant changes in hemispheric surface area and gyrification index in FXS compared to C; (2) linear regression analyses revealed significant negative correlations between CM and cognition; (3) significant CM differences between FXS and FXS+Aut associated with their distinctive behavioral phenotypes. These findings are critical in understanding the neuropathophysiology of one of the most common intellectual deficiency syndromes associated with altered cognition as they provide human in vivo information about genetic control of CM and cognition.

Retrotransposon activation contributes to fragile X premutation rCGG-mediated neurodegeneration

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder associated with fragile X premutation carriers. Previous studies have shown that fragile X rCGG repeats are sufficient to cause neurodegeneration and that the rCGG-repeat-binding proteins Pur α and heterogeneous nuclear ribonucleoprotein (hnRNP) A2/B1 could modulate rCGG-mediated neuronal toxicity. Mobile genetic elements or their remnants populate the genomes, and the activities of these elements are tightly controlled for the fitness of host genomes in different organisms. Here we provide both biochemical and genetic evidence to show that the activation of a specific retrotransposon, gypsy, can modulate rCGG-mediated neurodegeneration in an FXTAS Drosophila model. We find that one of the rCGG-repeat-binding proteins, hnRNP A2/B1, is involved in this process via interaction with heterochromatin protein 1. Knockdown of gypsy RNA by RNAi could suppress the neuronal toxicity caused by rCGG repeats. These data together point to a surprisingly active role for retrotransposition in neurodegeneration.

Regulation of molecular pathways in the Fragile X Syndrome: insights into Autism Spectrum Disorders

The Fragile X syndrome (FXS) is a leading cause of intellectual disability (ID) and autism. The disease is caused by mutations or loss of the Fragile X Mental Retardation Protein (FMRP), an RNA-binding protein playing multiple functions in RNA metabolism. The expression of a large set of neuronal mRNAs is altered when FMRP is lost, thus causing defects in neuronal morphology and physiology. FMRP regulates mRNA stability, dendritic targeting, and protein synthesis. At synapses, FMRP represses protein synthesis by forming a complex with the Cytoplasmic FMRP Interacting Protein 1 (CYFIP1) and the cap-binding protein eIF4E. Here, we review the clinical, genetic, and molecular aspects of FXS with a special focus on the receptor signaling that regulates FMRP-dependent protein synthesis. We further discuss the FMRP-CYFIP1 complex and its potential relevance for ID and autism.

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.

Fragile X-associated disorders: a clinical overview

Fragile X Syndrome (FraX) is the most common inherited cause of learning disability worldwide. FraX is an X-linked neuro-developmental disorder involving an unstable trinucleotide repeat expansion of cytosine guanine guanine (CGG). Individuals with the full mutation of FraX have >200 GG repeats with premutation carriers having 55-200 GG repeats. A wide spectrum of physical, behavioural, cognitive, psychiatric and medical problems have been associated with both full mutation and premutation carriers of FraX. In this review, we detail the clinical profile and examine the aetiology, epidemiology, neuropathology, neuroimaging findings and possible management strategies for individuals with both the full mutation and premutation of FraX.

CGG repeat in the FMR1 gene: size matters

The FMR1 gene contains a CGG repeat present in the 5'-untranslated region which can be unstable upon transmission to the next generation. The repeat is up to 55 CGGs long in the normal population. In patients with fragile X syndrome (FXS), a repeat length exceeding 200 CGGs (full mutation: FM) generally leads to methylation of the repeat and the promoter region, which is accompanied by silencing of the FMR1 gene. The absence of FMR1 protein, FMRP, seen in FM is the cause of the mental retardation in patients with FXS. The premutation (PM) is defined as 55-200 CGGs. Female PM carriers are at risk of developing primary ovarian insufficiency. Elderly PM carriers might develop a progressive neurodegenerative disorder called fragile X-associated tremor/ataxia syndrome (FXTAS). Although arising from the mutations in the same gene, distinct mechanisms lead to FXS (absence of FMRP), FXTAS (toxic RNA gain-of-function) and FXPOI. The pathogenic mechanisms thought to underlie these disorders are discussed. This review gives insight on the implications of all possible repeat length categories seen in fragile X families.

Induced pluripotent stem cells: a new revolution for clinical neurology?

Why specific neuronal populations are uniquely susceptible in neurodegenerative diseases remains a mystery. Brain tissue samples from patients are rarely available for testing, and animal models frequently do not recapitulate all features of a specific disorder; therefore, pathophysiological investigations are difficult. An exciting new avenue for neurological research and drug development is the discovery that patients' somatic cells can be reprogrammed to a pluripotent state; these cells are known as induced pluripotent stem cells. Once pluripotency is reinstated, cell colonies can be expanded and differentiated into specific neural populations. The availability of these cells enables the monitoring in vitro of temporal features of disease initiation and progression, and testing of new drug treatments on the patient's own cells. Hence, this swiftly growing area of research has the potential to contribute greatly to our understanding of the pathophysiology of neurodegenerative and neurodevelopmental diseases.

Nuclear accumulation of stress response mRNAs contributes to the neurodegeneration caused by Fragile X premutation rCGG repeats

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a neurodegenerative disorder seen in Fragile X premutation carriers. Previous studies found that Fragile X rCGG repeats are sufficient to cause neurodegeneration and that the rCGG repeat-binding proteins Pur α and hnRNP A2/B1 can modulate rCGG-mediated neuronal toxicity. To explore the role of Pur α in rCGG-mediated neurodegeneration further, we took a proteomic approach and identified more than 100 proteins that interact with Pur α. Of particular interest is Rm62, the Drosophila ortholog of p68 RNA helicase, which could modulate rCGG-mediated neurodegeneration. Here we show that rCGG repeats decreased the expression of Rm62 posttranscriptionally, leading to the nuclear accumulation of Hsp70 transcript, as well as additional mRNAs involved in stress and immune responses. Together these findings suggest that abnormal nuclear accumulation of these mRNAs, likely as a result of impaired nuclear export, could contribute to FXTAS pathogenesis.

Heads-up: new roles for the fragile X mental retardation protein in neural stem and progenitor cells

Fragile X syndrome (FXS) is the most common form of inherited mental retardation and is caused by the loss of function for Fragile X Mental Retardation Protein (FMRP), a selective RNA-binding protein with a demonstrated role in the localized translation of target mRNAs at synapses. Several recent studies provide compelling evidence for a new role of FMRP in the development of the nervous system, during neurogenesis. Using a multi-faceted approach and a variety of model systems ranging from cultured neurospheres and progenitor cells to in vivo Drosophila and mouse models these reports indicate that FMRP is required for neural stem and progenitor cell proliferation, differentiation, survival, as well as regulation of gene expression. Here we compare and contrast these recent reports and discuss the implications of FMRP's new role in embryonic and adult neurogenesis, including the development of novel therapeutic approaches to FXS and related neurological disorders such as autism.

One world, one woman: a transformational leader's approach to primary ovarian insufficiency

Lectureship endowment funds are created to honor major contributions that have clearly advanced a field. In some select cases they recognize the contributions of a transformational leader. Such was the case in the creation of the Wulf H. Utian Endowed Lectureship Fund. The express purpose of the fund is to provide travel to the annual meeting by a lecturer selected by the North American Menopause Society Scientific Program Committee. Wulf H. Utian changed the paradigm for menopause by creating an organization whose major purpose was to employ an integrated approach to the condition. Such an approach would benefit many areas of healthcare. This report summarizes my thoughts on how such an integrated approach might advance the field of primary ovarian insufficiency.

A voxel-based morphometry study of grey matter loss in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome is a neurodegenerative disorder that primarily affects older male premutation carriers of the fragile X mental retardation gene. Although its core symptoms are mainly characterized by motor problems such as intention tremor and gait ataxia, cognitive decline and psychiatric problems are also commonly observed. Past radiological and histological approaches have focused on prominent neurodegenerative changes in specific brain structures including the cerebellum and limbic areas. However, quantitative investigations of the regional structural abnormalities have not been performed over the whole brain. In this study, we adopted the voxel-based morphometry method together with regions of interest analysis for the cerebellum to examine the pattern of regional grey matter change in the male premutation carriers with and without fragile X-associated tremor/ataxia syndrome. In a comparison with healthy controls, we found striking grey matter loss of the patients with fragile X-associated tremor/ataxia syndrome in multiple regions over the cortical and subcortical structures. In the cerebellum, the anterior lobe and the superior posterior lobe were profoundly reduced in both vermis and hemispheres. In the cerebral cortex, clusters of highly significant grey matter reduction were found in the extended areas in the medial surface of the brain, including the dorsomedial prefrontal cortex, anterior cingulate cortex and precuneus. The other prominent grey matter loss was found in the lateral prefrontal cortex, orbitofrontal cortex, amygdala and insula. Although the voxel-wise comparison between the asymptomatic premutation group and healthy controls did not reach significant difference, a regions of interest analysis revealed significant grey matter reduction in anterior subregions of the cerebellar vermis and hemisphere in the asymptomatic premutation group. Correlation analyses using behavioural scales of the premutation groups showed significant associations between grey matter loss in the left amygdala and increased levels of obsessive-compulsiveness and depression, and between decreased grey matter in the left inferior frontal cortex and anterior cingulate cortex and poor working memory performance. Furthermore, regression analyses revealed a significant negative effect of CGG repeat size on grey matter density in the dorsomedial frontal regions. A significant negative correlation with the clinical scale for the severity of fragile X-associated tremor/ataxia syndrome was found in a part of the vermis. These observations reveal the anatomical patterns of the neurodegenerative process that underlie the motor, cognitive and psychiatric problems of fragile X-associated tremor/ataxia syndrome, together with incipient structural abnormalities that may occur before the clinical onset of this disease.

Clinical phenotypes of a juvenile sibling pair carrying the fragile X premutation

Individuals with alleles containing 55-200 CGG repeats in the fragile X mental retardation (FMR1) gene are premutation carriers. The premutation allele has been shown to lead to a number of types of clinical involvement, including shyness, anxiety, social deficits, attention deficit hyperactivity disorder (ADHD), and executive function deficits. Some of these problems could be due to mild deficits of the fragile X protein (FMRP) and a possible developmental effect of the elevated FMR1 mRNA observed in carriers. In addition, two abnormal phenotypes specific to the premutation have been described. Primary ovarian insufficiency (FXPOI), defined by cessation of menses prior to age 40, occurs in 20% of females with the premutation. The other phenotype, fragile X-associated tremor/ataxia syndrome (FXTAS), affects some older adult premutation carriers. Premutation females typically have one expanded allele (≥55 CGG repeats) and one normal allele (≤54 CGG repeats). This study describes the cognitive, behavioral, and molecular profile of a female with two alleles in the premutation range (60 and 67 CGG repeats) in comparison to her brother with a similar premutation size (65 CGG repeats). Both exhibited high IQ scores, anxiety, and some physical features associated with fragile X syndrome. This comparison allows us to examine the effect of the premutation in this male-female pair while controlling for environmental and background genetic factors.

Lifetime prevalence of mood and anxiety disorders in fragile X premutation carriers

OBJECTIVE

The authors studied the lifetime prevalence of DSM-IV-TR psychiatric disorders in a population of adults with the fragile X premutation.

METHOD

The Structured Clinical Interview for DSM-IV was conducted, from 2007-2008, in 85 individuals with the fragile X premutation, 47 with the fragile X-associated tremor/ataxia syndrome (FXTAS; 33 male, 14 female; mean age = 66 years) and 38 without FXTAS (16 male, 22 female; mean age = 52 years). Lifetime prevalence for mood and anxiety disorders among carriers with and without FXTAS was compared to available age-specific population estimates from the National Comorbidity Survey Replication (NCS-R).

RESULTS

Among participants with FXTAS, 30 (65%) met lifetime DSM-IV-TR criteria for a mood disorder; 24 (52%) met lifetime DSM-IV-TR criteria for an anxiety disorder. Among the non-FXTAS participants, there were 15 instances of lifetime mood disorder (42%) and 18 of lifetime anxiety disorder (47%). When compared to age-specific NCS-R data, the lifetime prevalences of any mood disorder (P < .0001), major depressive disorder (P < .0001), any anxiety disorder (P < .0001), panic disorder (P = .006), specific phobia (P = .0003), and posttraumatic stress disorder (P = .004) were significantly higher in participants with FXTAS. The lifetime rates of social phobia in individuals with the premutation without FXTAS were significantly higher than NCS-R data (P = .001).

CONCLUSIONS

This sample of carriers of the fragile X premutation had a notably high lifetime risk of mood and anxiety disorders. Mood and anxiety disorders may be part of the clinical phenotype of the fragile X premutation conditions, especially in carriers with FXTAS. Clinicians encountering these patients are advised to consider FXTAS as a neuropsychiatric syndrome as well as a neurologic disorder.