Autism: the point of view from fragile X studies

Using Zebrafish to Model Autism Spectrum Disorder: A Comparison of ASD Risk Genes Between Zebrafish and Their Mammalian Counterparts

Autism spectrum disorders (ASDs) are a highly variable and complex set of neurological disorders that alter neurodevelopment and cognitive function, which usually presents with social and learning impairments accompanied with other comorbid symptoms like hypersensitivity or hyposensitivity, or repetitive behaviors. Autism can be caused by genetic and/or environmental factors and unraveling the etiology of ASD has proven challenging, especially given that different genetic mutations can cause both similar and different phenotypes that all fall within the autism spectrum. Furthermore, the list of ASD risk genes is ever increasing making it difficult to synthesize a common theme. The use of rodent models to enhance ASD research is invaluable and is beginning to unravel the underlying molecular mechanisms of this disease. Recently, zebrafish have been recognized as a useful model of neurodevelopmental disorders with regards to genetics, pharmacology and behavior and one of the main foundations supporting autism research (SFARI) recently identified 12 ASD risk genes with validated zebrafish mutant models. Here, we describe what is known about those 12 ASD risk genes in human, mice and zebrafish to better facilitate this research. We also describe several non-genetic models including pharmacological and gnotobiotic models that are used in zebrafish to study ASD.

Differentiating social preference and social anxiety phenotypes in fragile X syndrome using an eye gaze analysis: a pilot study

Background

Fragile X syndrome (FXS) is the leading inherited cause of autism spectrum disorder, but there remains debate regarding the clinical presentation of social deficits in FXS. The aim of this study was to compare individuals with FXS to typically developing controls (TDC) and individuals with idiopathic autism spectrum disorder (ASD) across two social eye tracking paradigms.

Methods

Individuals with FXS and age- and gender-matched TDC and individuals with idiopathic ASD completed emotional face and social preference eye tracking tasks to evaluate gaze aversion and social interest, respectively. Participants completed a battery of cognitive testing and caregiver-reported measures for neurobehavioral characterization.

Results

Individuals with FXS exhibited reduced eye and increased mouth gaze to emotional faces compared to TDC. Gaze aversive findings were found to correlate with measures of anxiety, social communication deficits, and behavioral problems. In the social interest task, while individuals with idiopathic ASD showed significantly less social preference, individuals with FXS displayed social preference similar to TDC.

Conclusions

These findings suggest fragile X syndrome social deficits center on social anxiety without the prominent reduction in social interest associated with autism spectrum disorder. Specifically designed eye tracking techniques clarify the nature of social deficits in fragile X syndrome and may have applications to improve phenotyping and evaluate interventions targeting social functioning impairments.

Specificity: A Phenotypic Comparison of Communication-Relevant Domains Between Youth With Down Syndrome and Fragile X Syndrome

Despite the shared presence of an intellectual disability (ID), there is a growing literature documenting important phenotypic differences between Down syndrome (DS) and fragile X syndrome (FXS). These conclusions, however, are based on a synthesis across studies, each of which typically includes only measures of a limited number of constructs, and with differing participant characteristics. Firmer conclusions regarding specific phenotypes require a single comprehensive multi-domain assessment of participants with the syndrome groups being well matched on chronological age (CA) and cognitive functioning. The current study was designed to fill this gap by assessing several important cognitive and behavioral domains relevant to communication, such as: structural language skills, false belief understanding, as well as pragmatics and behavioral difficulties, in 30 adolescents of both sexes with DS and 39 males with FXS, matched on CA and nonverbal (NV) cognition. After statistically controlling for NV cognition, we did not find significant syndrome differences in expressive and receptive structural language or false belief understanding. In contrast, participants with DS displayed less stereotyped language and fewer behavioral difficulties compared to males with FXS. Within-syndrome associations among the targeted domains are described. Finally, females with DS were less impaired than males with DS in almost all structural language domains, whereas no significant sex-related differences were observed in NV cognition, false belief understanding, pragmatics, or behavior. Clinical and methodological implications of the findings are discussed.

Evaluating Sensory Processing in Fragile X Syndrome: Psychometric Analysis of the Brain Body Center Sensory Scales (BBCSS)

Individuals with fragile X syndrome (FXS), especially those co-diagnosed with autism spectrum disorder (ASD), face many sensory processing challenges. However, sensory processing measures informed by neurophysiology are lacking. This paper describes the development and psychometric properties of a parent/caregiver report, the Brain-Body Center Sensory Scales (BBCSS), based on Polyvagal Theory. Parents/guardians reported on 333 individuals with FXS, 41% with ASD features. Factor structure using a split-sample exploratory-confirmatory design conformed to neurophysiological predictions. Internal consistency, test-retest, and inter-rater reliability were good to excellent. BBCSS subscales converged with the Sensory Profile and Sensory Experiences Questionnaire. However, data also suggest that BBCSS subscales reflect unique features related to sensory processing. Individuals with FXS and ASD features displayed more sensory challenges on most subscales.

Do psychoactive drugs have a therapeutic role in compulsivity? Studies on schedule-induced polydipsia

RATIONALE

Clinical studies have shown that some psychoactive recreational drugs have therapeutic applications in anxiety, depression, and schizophrenia. However, to date, there are few studies on the therapeutic potential efficacy of recreational drugs in compulsive neuropsychiatric disorders.

OBJECTIVES

We explored the therapeutic potential of different psychoactive and psychedelic drugs in a preclinical model of compulsive behavior.

METHODS

Outbred male Wistar rats were selected as either high (HD) or low (LD) drinkers according to their behavior in schedule-induced polydipsia (SIP). Subsequently, we assessed the effects of acute administration of scopolamine (0.125, 0.25, and 0.5 mg/kg), methamphetamine (0.25, 0.5, 1.25, and 2.5 mg/kg), ketamine (1.25, 2.5, 5, and 10 mg/kg), cannabidiol (1 and 3 mg/kg), WIN21255-2 (0.5, 075, and 1 mg/kg), and AM404 (0.25 and 0.5 mg/kg) on compulsive drinking in SIP.

RESULTS

Scopolamine reduced dose-dependent compulsive drinking in HD compared with LD rats in SIP. Methamphetamine induced a dose-dependent inverted U-curve effect in both groups, in which lower doses increased and higher doses reduced compulsive drinking in SIP. Ketamine, cannabidiol, WIN21255-2, and AM404 did not have any relevant effects in SIP.

CONCLUSIONS

These data provide new evidence that low doses of scopolamine and intermediate doses of methamphetamine might therapeutically reduce compulsive behaviors and suggest that there is not a direct participation of the endocannabinoid system in compulsive behavior on SIP. The research in the underlying neurochemical mechanisms of these psychoactive drugs might provide an additional insight on new therapeutic targets in compulsive neuropsychiatric disorders.

Developmental Emergence of Phenotypes in the Auditory Brainstem Nuclei of Fmr1 Knockout Mice

Fragile X syndrome (FXS), the most common monogenic cause of autism, is often associated with hypersensitivity to sound. Several studies have shown abnormalities in the auditory brainstem in FXS; however, the emergence of these auditory phenotypes during development has not been described. Here, we investigated the development of phenotypes in FXS model [Fmr1 knockout (KO)] mice in the ventral cochlear nucleus (VCN), medial nucleus of the trapezoid body (MNTB), and lateral superior olive (LSO). We studied features of the brainstem known to be altered in FXS or Fmr1 KO mice, including cell size and expression of markers for excitatory (VGLUT) and inhibitory (VGAT) synapses. We found that cell size was reduced in the nuclei with different time courses. VCN cell size is normal until after hearing onset, while MNTB and LSO show decreases earlier. VGAT expression was elevated relative to VGLUT in the Fmr1 KO mouse MNTB by P6, before hearing onset. Because glial cells influence development and are altered in FXS, we investigated their emergence in the developing Fmr1 KO brainstem. The number of microglia developed normally in all three nuclei in Fmr1 KO mice, but we found elevated numbers of astrocytes in Fmr1 KO in VCN and LSO at P14. The results indicate that some phenotypes are evident before spontaneous or auditory activity, while others emerge later, and suggest that Fmr1 acts at multiple sites and time points in auditory system development.

Sensory processing in autism spectrum disorders and Fragile X syndrome-From the clinic to animal models

Brains are constantly flooded with sensory information that needs to be filtered at the pre-attentional level and integrated into endogenous activity in order to allow for detection of salient information and an appropriate behavioral response. People with Autism Spectrum Disorder (ASD) or Fragile X Syndrome (FXS) are often over- or under-reactive to stimulation, leading to a wide range of behavioral symptoms. This altered sensitivity may be caused by disrupted sensory processing, signal integration and/or gating, and is often being neglected. Here, we review translational experimental approaches that are used to investigate sensory processing in humans with ASD and FXS, and in relevant rodent models. This includes electroencephalographic measurement of event related potentials, neural oscillations and mismatch negativity, as well as habituation and pre-pulse inhibition of startle. We outline robust evidence of disrupted sensory processing in individuals with ASD and FXS, and in respective animal models, focusing on the auditory sensory domain. Animal models provide an excellent opportunity to examine common mechanisms of sensory pathophysiology in order to develop therapeutics.

A Subset of Autism-Associated Genes Regulate the Structural Stability of Neurons

Autism spectrum disorder (ASD) comprises a range of neurological conditions that affect individuals’ ability to communicate and interact with others. People with ASD often exhibit marked qualitative difficulties in social interaction, communication, and behavior. Alterations in neurite arborization and dendritic spine morphology, including size, shape, and number, are hallmarks of almost all neurological conditions, including ASD. As experimental evidence emerges in recent years, it becomes clear that although there is broad heterogeneity of identified autism risk genes, many of them converge into similar cellular pathways, including those regulating neurite outgrowth, synapse formation and spine stability, and synaptic plasticity. These mechanisms together regulate the structural stability of neurons and are vulnerable targets in ASD. In this review, we discuss the current understanding of those autism risk genes that affect the structural connectivity of neurons. We sub-categorize them into (1) cytoskeletal regulators, e.g., motors and small RhoGTPase regulators; (2) adhesion molecules, e.g., cadherins, NCAM, and neurexin superfamily; (3) cell surface receptors, e.g., glutamatergic receptors and receptor tyrosine kinases; (4) signaling molecules, e.g., protein kinases and phosphatases; and (5) synaptic proteins, e.g., vesicle and scaffolding proteins. Although the roles of some of these genes in maintaining neuronal structural stability are well studied, how mutations contribute to the autism phenotype is still largely unknown. Investigating whether and how the neuronal structure and function are affected when these genes are mutated will provide insights toward developing effective interventions aimed at improving the lives of people with autism and their families.

Three Faces of Fragile X

Fragile X syndrome (FXS) is the first of 3 syndromes identified as a health condition related to fragile X mental retardation (FMR1) gene dysfunction. The other 2 syndromes are fragile X-associated primary ovarian insufficiency syndrome (FXPOI) and fragile X-associated tremor/ataxia syndrome (FXTAS), which together are referred to as fragile X-associated disorders (FXDs). Collectively, this group comprises the 3 faces of fragile X. Even though the 3 conditions share a common genetic defect, each one is a separate health condition that results in a variety of body function impairments such as motor delay, musculoskeletal issues related to low muscle tone, coordination limitations, ataxia, tremor, undefined muscle aches and pains, and, for FXTAS, a late-onset neurodegeneration. Although each FXD condition may benefit from physical therapy intervention, available evidence as to the efficacy of intervention appropriate to FXDs is lacking. This perspective article will discuss the genetic basis of FMR1 gene dysfunction and describe health conditions related to this mutation, which have a range of expressions within a family. Physical therapy concerns and possible assessment and intervention strategies will be introduced. Understanding the intergenerational effect of the FMR1 mutation with potential life-span expression is a key component to identifying and treating the health conditions related to this specific genetic condition.

Change in the Behavioral Phenotype of Adolescents and Adults with FXS: Role of the Family Environment

The present study examined trajectories of adaptive behavior, behavior problems, psychological symptoms, and autism symptoms in adolescents and adults with fragile X syndrome (n = 147) over a three-year period. Adaptive behavior significantly increased over time, particularly for adolescents, and the severity of behavior problems decreased over time. Family environmental factors predicted phenotypic variables net of gender, intellectual disability status, and medication use. Maternal warmth was associated with higher levels of adaptive behavior, lower levels of autism symptoms, and decreases in behavior problems over time. Maternal depressive symptoms and criticism were associated with higher levels of psychological symptoms. Implications for interventions are discussed.

Looping Genomes: Diagnostic Change and the Genetic Makeup of the Autism Population

This article builds on Hacking's framework of "dynamic nominalism" to show how knowledge about biological etiology can interact with the "kinds of people" delineated by diagnostic categories in ways that "loop" or modify both over time. The authors use historical materials to show how "geneticization" played a crucial role in binding together autism as a biosocial community and how evidence from genetics research later made an important contribution to the diagnostic expansion of autism. In the second part of the article, the authors draw on quantitative and qualitative analyses of autism rates over time in several rare conditions that are delineated strictly according to genomic mutations in order to demonstrate that these changes in diagnostic practice helped to both increase autism's prevalence and create its enormous genetic heterogeneity. Thus, a looping process that began with geneticization and involved the social effects of genetics research itself transformed the autism population and its genetic makeup.

Symptoms of Autism in Males with Fragile X Syndrome: A Comparison to Nonsyndromic ASD Using Current ADI-R Scores

Symptoms of autism are frequent in males with fragile X syndrome (FXS), but it is not clear whether symptom profiles differ from those of nonsyndromic ASD. Using individual item scores from the Autism Diagnostic Inventory-Revised, we examined which current symptoms of autism differed in boys with FXS relative to same-aged boys diagnosed with nonsyndromic ASD. In addition, different subsamples of participants were matched on autism diagnostic status and severity of autism symptoms. Between-group comparisons revealed that boys with FXS showed significantly less impairment in Social Smiling than did age-, diagnostic-, and severity-matched boys with nonsyndromic ASD. Severity-matched boys with FXS showed more impairment in complex mannerisms than did boys with nonsyndromic ASD. Behavioral differences between FXS and nonsyndromic ASD may be of theoretical importance in understanding the causes and correlates of ASD in FXS and in developing and implementing appropriate treatments.

Autism Symptomatology in Boys with Fragile X Syndrome: A Cross Sectional Developmental Trajectories Comparison with Nonsyndromic Autism Spectrum Disorder

Although males with fragile X syndrome (FXS) are frequently described as demonstrating autism symptomatology, there is much debate regarding whether the behavioral symptoms representing the core domains of autism are the result of the same or different underlying neurological/psychological mechanisms. The present study used a cross-sectional developmental trajectories approach to compare the profiles of autism symptomatology relative to chronological age (CA), nonverbal IQ, and expressive vocabulary ability between individuals with FXS and individuals with nonsyndromic ASD. Results suggest that the onset of autism symptoms and their developmental trajectories in males with FXS differ in important ways as a function of CA, nonverbal cognitive ability, and expressive vocabulary relative to males with nonsyndromic ASD. Theoretical and clinical implications are discussed.

Do Children With Fragile X Syndrome Show Declines or Plateaus in Adaptive Behavior?

This study explores if children with fragile X syndrome (FXS) show advances, declines, or plateaus in adaptive behavior over time and the relationship of nonverbal cognitive abilities and autistic behavior on these trajectories. Parents of 55 children with FXS completed the Vineland Adaptive Behavior Scales ( Sparrow, Balla, & Cicchetti, 1984 ; Sparrow, Cicchetti, & Balla, 2005 ) between 3 and 6 times from 2 to 10 years of age. Using raw scores, results indicate that about half of the sample showed advances in adaptive behavior, whereas the other half showed declines, indicating a regression in skills. Children who were more cognitively advanced and had less autistic behaviors had higher trajectories. Understanding the developmental course of adaptive behavior in FXS has implications for educational planning and intervention, especially for those children showing declines.

Developing Medications Targeting Glutamatergic Dysfunction in Autism: Progress to Date

Pharmacologic treatments targeting specific molecular mechanisms relevant for autism spectrum disorder (ASD) are beginning to emerge in early drug development. This article reviews the evidence for the disruption of glutamatergic neurotransmission in animal models of social deficits and summarizes key pre-clinical and clinical efforts in developing pharmacologic interventions based on modulation of glutamatergic systems in individuals with ASD. Understanding the pathobiology of the glutamatergic system has led to the development of new investigational treatments for individuals with ASD. Specific examples of medications that modulate the glutamatergic system in pre-clinical and clinical studies are described. Finally, we discuss the limitations of current strategies and future opportunities in developing medications targeting the glutamatergic system for treating individuals with ASD.

Auditory processing in fragile x syndrome

Fragile X syndrome (FXS) is an inherited form of intellectual disability and autism. Among other symptoms, FXS patients demonstrate abnormalities in sensory processing and communication. Clinical, behavioral, and electrophysiological studies consistently show auditory hypersensitivity in humans with FXS. Consistent with observations in humans, the Fmr1 KO mouse model of FXS also shows evidence of altered auditory processing and communication deficiencies. A well-known and commonly used phenotype in pre-clinical studies of FXS is audiogenic seizures. In addition, increased acoustic startle response is seen in the Fmr1 KO mice. In vivo electrophysiological recordings indicate hyper-excitable responses, broader frequency tuning, and abnormal spectrotemporal processing in primary auditory cortex of Fmr1 KO mice. Thus, auditory hyper-excitability is a robust, reliable, and translatable biomarker in Fmr1 KO mice. Abnormal auditory evoked responses have been used as outcome measures to test therapeutics in FXS patients. Given that similarly abnormal responses are present in Fmr1 KO mice suggests that cellular mechanisms can be addressed. Sensory cortical deficits are relatively more tractable from a mechanistic perspective than more complex social behaviors that are typically studied in autism and FXS. The focus of this review is to bring together clinical, functional, and structural studies in humans with electrophysiological and behavioral studies in mice to make the case that auditory hypersensitivity provides a unique opportunity to integrate molecular, cellular, circuit level studies with behavioral outcomes in the search for therapeutics for FXS and other autism spectrum disorders.

Influences on maternal responsivity in mothers of children with fragile X syndrome

This study investigated the influence of maternal and child variables on the maternal responsivity of 55 mothers with young children with fragile X syndrome. Data included video observations of mother-child interactions in four different contexts, standardized assessments with the children, and standardized questionnaires for the mothers. The video observations were coded for child communication acts; maternal responsivity was coded at two levels: a more general measure and a behavior-by-behavior measure. Results indicated that child developmental level and language ability strongly influenced behavior-by-behavior responsivity, while maternal IQ was the strongest predictor of both general and behavior-by-behavior responsivity, after controlling for child developmental level.

Investigating word learning in fragile X syndrome: a fast-mapping study

Fast-mapping paradigms have not been used previously to examine the process of word learning in boys with fragile X syndrome (FXS), who are likely to have intellectual impairment, language delays, and symptoms of autism. In this study, a fast-mapping task was used to investigate associative word learning in 4- to 10-year-old boys with FXS relative to younger typically developing boys and age-matched boys with autism spectrum disorders (ASD). Task performance exceeded chance levels for all groups; however, boys with FXS outperformed boys with ASD, despite having lower levels of nonverbal cognition. Memory task demands significantly impacted performance only for boys with typical development. For boys with FXS or ASD, fast-mapping uniquely accounted for small but significant variance in concurrent levels of vocabulary comprehension as did chronological age and nonverbal IQ, but not autism severity. Understanding the fast-mapping process has implications for designing interventions to support word learning and language acquisition in these populations.

Autism spectrum disorders: the quest for genetic syndromes

Autism spectrum disorders (ASD) are a heterogeneous group of neurodevelopmental disabilities with various etiologies, but with a heritability estimate of more than 90%. Although the strong correlation between autism and genetic factors has been long established, the exact genetic background of ASD remains unclear. A number of genetic syndromes manifest ASD at higher than expected frequencies compared to the general population. These syndromes account for more than 10% of all ASD cases and include tuberous sclerosis, fragile X, Down, neurofibromatosis, Angelman, Prader-Willi, Williams, Duchenne, etc. Clinicians are increasingly required to recognize genetic disorders in individuals with ASD, in terms of providing proper care and prognosis to the patient, as well as genetic counseling to the family. Vice versa, it is equally essential to identify ASD in patients with genetic syndromes, in order to ensure correct management and appropriate educational placement. During investigation of genetic syndromes, a number of issues emerge: impact of intellectual disability in ASD diagnoses, identification of autistic subphenotypes and differences from idiopathic autism, validity of assessment tools designed for idiopathic autism, possible mechanisms for the association with ASD, etc. Findings from the study of genetic syndromes are incorporated into the ongoing research on autism etiology and pathogenesis; different syndromes converge upon common biological backgrounds (such as disrupted molecular pathways and brain circuitries), which probably account for their comorbidity with autism. This review paper critically examines the prevalence and characteristics of the main genetic syndromes, as well as the possible mechanisms for their association with ASD.

Evidence of a distinct behavioral phenotype in young boys with fragile X syndrome and autism

OBJECTIVE

How does the behavioral expression of autism in fragile X syndrome (FXS + Aut) compare with idiopathic autism (iAut)? Although social impairments and restricted, repetitive behaviors are common to these variants of autism, closer examination of these symptom domains may reveal meaningful similarities and differences. To this end, the specific behaviors comprising the social and repetitive behavioral domains in young children with FXS + Aut and iAut were profiled.

METHOD

Twenty-three male subjects 3 to 5 years old with FXS + Aut were matched by age to a group of 38 boys with iAut. Repetitive behavior was assessed using the Repetitive Behavior Scales-Revised. Social behavior was evaluated using Autism Diagnostic Observation Schedule social item severity scores.

RESULTS

Rates of stereotypy, self-injury, and sameness behaviors did not differ between groups, whereas compulsive and ritual behavior scores were significantly lower for subjects with FXS + Aut compared with those with iAut. Those with FXS + Aut scored significantly lower (less severe) than the iAut group on five Autism Diagnostic Observation Schedule measurements of social behavior: gaze integration, quality of social overtures, social smile, facial expressions, and response to joint attention.

CONCLUSIONS

The behavioral phenotype of FXS + Aut and iAut are most similar with respect to lower-order (motoric) restricted, repetitive behaviors and social approach, but differ in more complex forms of restricted, repetitive behaviors and some social response behaviors. These findings highlight the phenotypic heterogeneity of autism overall and its unique presentation in an etiologically distinct condition.

Profiles of receptive and expressive language abilities in boys with comorbid fragile X syndrome and autism

Abstract The authors examined receptive and expressive language profiles for a group of verbal male children and adolescents who had fragile X syndrome along with varying degrees of autism symptoms. A categorical approach for assigning autism diagnostic classification, based on the combined use of the Autism Diagnostic Interview-Revised and the Autism Diagnostic Observation Schedule (ADOS), and a continuous approach for representing autism symptom severity, based on ADOS severity scores, were used in 2 separate sets of analyses. All analyses controlled for nonverbal IQ and chronological age. Nonverbal IQ accounted for significant variance in all language outcomes with large effect sizes. Results of the categorical analyses failed to reveal an effect of diagnostic group (fragile X syndrome-autism, fragile X syndrome-no autism) on standardized language test performance. Results of the continuous analyses revealed a negative relationship between autism symptom severity and all of the standardized language measures. Implications for representing autism symptoms in fragile X syndrome research are considered.

The modulation of fragile X behaviors by the muscarinic M4 antagonist, tropicamide

Muscarinic acetylcholine receptors (mAChR) are G protein-coupled receptors (M1-M5), grouped together into two functional classes, based on their G protein interaction. Although ubiquitously expressed in the CNS, the M4 protein shows highest expression in the neostriatum, cortex, and hippocampus. Electrophysiological and biochemical studies have provided evidence for overactive mAChR signaling in the fragile X knock-out (Fmr1KO) mouse model, and this has been hypothesized to contribute to the phenotypes seen in Fmr1KO mice. To address this hypothesis we used an M4 antagonist, tropicamide, to reduce the activity through the M4 mAChR and investigated the behavioral response in the Fmr1KO animals. Data from the marble-burying assay have shown that tropicamide treatment resulted in a decreased number of marbles buried in the wild-type (WT) and in the knockout (KO) animals. Results from the open field assay indicated that tropicamide increases activity in both the WT and KO mice. In the passive avoidance assay, tropicamide treatment resulted in the improvement of performance in both the WT and the KO animals at the lower doses (2 and 5 mg/kg), and the drug was shown to be important for the acquisition and not the consolidation process. Lastly, we observed that tropicamide causes a significant decrease in the percentage of audiogenic seizures in the Fmr1KO animals. These results suggest that pharmacological antagonism of the M4 receptor modulates select behavioral responses in the Fmr1KO mice.

Modulation of behavioral phenotypes by a muscarinic M1 antagonist in a mouse model of fragile X syndrome

RATIONALE

Muscarinic acetylcholine receptors (mAChR) are G protein-coupled receptors, widely expressed in the CNS. Electrophysiological and molecular studies have provided evidence for overactive M1 receptor signaling in the fragile X knockout (Fmr1 KO) mouse model, suggesting the involvement of the M1 receptors in fragile X syndrome. Overactive signaling through the M1 receptor has been hypothesized to contribute to the phenotypes seen in fragile X mice.

OBJECTIVE

We investigated the modulation of behavioral responses in the Fmr1 KO animals by reducing the activity through the muscarinic M1 receptor using the pharmacological agent dicyclomine, an M1 antagonist.

METHODS

The behavioral assays used to investigate the pharmacological effects include marble burying (perseverative behavior), open-field exploration (activity), passive avoidance (learning and memory), prepulse inhibition (sensorimotor gating), and audiogenic seizures.

RESULTS

Data from the marble-burying assay suggests that treatment with dicyclomine results in a decrease in the number of marbles buried in the wild-type and in the KO animals. To examine the possibility of drug-induced sedation, overall activity was measured in an open-field chamber. Dicyclomine only increases activity at a dose of 20 mg/kg in the wild-type mice but did not affect exploration in the KO animals. Lastly, we observed that dicyclomine causes a significant decrease in the percentage of audiogenic seizures in the Fmr1 KO animals.

CONCLUSION

Our findings suggest that pharmacologically reducing the activity through the mAChR M1 alters select behavioral responses in the Fmr1 KO mice.

Genetic studies in children with intellectual disability and autistic spectrum of disorders

Autism is one of the five disorders that falls under the umbrella of Pervasive Developmental Disorders (PDD) or Autism Spectrum Disorder (ASD), a category of neurological disorders characterized by “severe and pervasive impairment in several areas of development.” ASD is characterized by varying degrees of impairment in communication skills, social interaction and restricted, repetitive stereotyped patterns of behavior. The five disorders under PDD are autistic disorder, Asperger's disorder, childhood disintegrative disorder, Rett's disorder and PDD-not otherwise specified. ASD can often be reliably detected by the age of 3 years and, in some cases, as early as 18 months. The appearance of any warning signs of ASD is reason to have the child evaluated by a professional specializing in these disorders.

Altered zinc transport disrupts mitochondrial protein processing/import in fragile X-associated tremor/ataxia syndrome

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a late-onset neurodegenerative disorder that affects individuals who are carriers of small CGG premutation expansions in the fragile X mental retardation 1 (FMR1) gene. Mitochondrial dysfunction was observed as an incipient pathological process occurring in individuals who do not display overt features of FXTAS (1). Fibroblasts from premutation carriers had lower oxidative phosphorylation capacity (35% of controls) and Complex IV activity (45%), and higher precursor-to-mature ratios (P:M) of nDNA-encoded mitochondrial proteins (3.1-fold). However, fibroblasts from carriers with FXTAS symptoms presented higher FMR1 mRNA expression (3-fold) and lower Complex V (38%) and aconitase activities (43%). Higher P:M of ATPase β-subunit (ATPB) and frataxin were also observed in cortex from patients that died with FXTAS symptoms. Biochemical findings observed in FXTAS cells (lower mature frataxin, lower Complex IV and aconitase activities) along with common phenotypic traits shared by Friedreich's ataxia and FXTAS carriers (e.g. gait ataxia, loss of coordination) are consistent with a defective iron homeostasis in both diseases. Higher P:M, and lower ZnT6 and mature frataxin protein expression suggested defective zinc and iron metabolism arising from altered ZnT protein expression, which in turn impairs the activity of mitochondrial Zn-dependent proteases, critical for the import and processing of cytosolic precursors, such as frataxin. In support of this hypothesis, Zn-treated fibroblasts showed a significant recovery of ATPB P:M, ATPase activity and doubling time, whereas Zn and desferrioxamine extended these recoveries and rescued Complex IV activity.

Maternal immune activation and autism spectrum disorder: interleukin-6 signaling as a key mechanistic pathway

An emerging area of research in autism spectrum disorder (ASD) is the role of prenatal exposure to inflammatory mediators during critical developmental periods. Epidemiological data has highlighted this relationship showing significant correlations between prenatal exposure to pathogens, including influenza, and the occurrence of ASD. Although there has not been a definitive molecular mechanism established, researchers have begun to investigate this relationship as animal models of maternal infection have support- ed epidemiological findings. Several groups utilizing these animal models have found that activation of the maternal immune system, termed maternal immune activation (MIA), and more specifically the exposure of the developing fetus to maternal cytokines precipitate the neurological, immunological and behavioral abnormalities observed in the offspring of these animals. These abnormalities have correlated with clinical findings of immune dysregulation, neurological and behavioral abnormalities in some autistic individuals. Additionally, researchers have observed genetic variations in these models in genes which regulate neurological and immunological development, similar to what is observed clinically in ASD. Altogether, the role of MIA and cytokine dysregulation, as a key mediator in the neuropathological, behavioral and possibly genetic irregularities observed clinically in autism are important factors that warrant further investigation.

Evidence of mitochondrial dysfunction in fragile X-associated tremor/ataxia syndrome

FXTAS (fragile X-associated tremor/ataxia syndrome) is a late-onset neurodegenerative disorder that affects individuals who are carriers of premutation expansions (55-200 CGG repeats) in the 5' untranslated region of the FMR1 (fragile X mental retardation 1) gene. The role of MD (mitochondrial dysfunction) in FXTAS was evaluated in fibroblasts and brain samples from premutation carriers with and without FXTAS symptoms, with a range of CGG repeats. This study resulted in several important conclusions: (i) decreased NAD- and FAD-linked oxygen uptake rates and uncoupling between electron transport and synthesis of ATP were observed in fibroblasts from premutation carriers; (ii) a lower expression of mitochondrial proteins preceded both in age and in CGG repeats the appearance of overt clinical involvement; (iii) the CGG repeat size required for altered mitochondrial protein expression was also smaller than that required to produce brain intranuclear inclusions from individuals with the premutation who died, suggesting that MD is an incipient pathological process occurring in individuals who do not display overt features of FXTAS; and (iv) on the basis of the CGG repeats, MD preceded the increase in oxidative/nitrative stress damage, indicating that the latter is a late event. MD in carriers of small CGG repeats, even when the allele size is not sufficient to produce FXTAS, may predispose them to other disorders (e.g. Parkinson's disease) that are likely to involve MD, and to environmental stressors, which may trigger the development of FXTAS symptoms. Detection of MD is of critical importance to the management of FXTAS, since it opens up additional treatment options for this disorder.

Brain morphology in autism and fragile X syndrome correlates with social IQ: first report from the Canadian-Swiss-Egyptian Neurodevelopmental Study

Fragile X syndrome shares most of the behavioral phenotypic similarities with autism. How are these similarities reflected in brain morphology? A total of 10 children with autism and 7 with fragile X underwent morphological (T1) 1.5-T magnetic resonance imaging (MRI). The authors found no significant difference in total brain volumes, regional volumes, gyrification index, sulcul depth, and cerebral cortical thickness. However, children with autism showed significant decrease in the medial prefrontal bilaterally and the left anterior cingulate cortices. Regression analysis revealed positive correlation between the medial prefrontal cortical thickness and the social IQ. The authors suggest that the difference between the 2 groups in the medial prefrontal and anterior cingulate cortices thickness may entail an altered social cognitive style. Functional MRI studies directly differentiating between social indifference (autism) and social avoidance (fragile X) are needed to further characterize the spectrum of social abnormalities between these 2 groups.

Expressive language in male adolescents with fragile X syndrome with and without comorbid autism

BACKGROUND

Approximately one-quarter of individuals with fragile X syndrome (FXS) meet diagnostic criteria for autism; however, it is unclear whether individuals with comorbid FXS and autism are simply more severely affected than their peers with only FXS or whether they have qualitatively different profiles of behavioural impairments. To address this issue, variation in the FXS linguistic phenotype was examined in males with FXS with and without autism. The syndrome-specificity of the expressive language impairment of both groups of those with FXS was assessed in relation to Down syndrome. The extent to which different language sampling contexts affected expressive language in each diagnostic group was also examined.

METHOD

Spontaneous language samples were collected from male adolescents with FXS without autism (n = 20), comorbid FXS and autism (n = 8), and Down syndrome (n = 16). Syntactic complexity (indexed by mean length of utterance), expressive vocabulary (indexed by lexical diversity), talkativeness, fluency and intelligibility were assessed in two contexts: conversation and narration. Groups were matched on non-verbal IQ, non-verbal mental age and chronological age to allow the assessment of relative strengths and weaknesses across language variables.

RESULTS

Males with comorbid FXS and autism were less intelligible than males with only FXS; no other differences between these two groups were found. Participants' performance differed across contexts for syntactic complexity, lexical diversity, talkativeness and fluency.

CONCLUSIONS

These findings contribute to existing research on the behavioural profiles of individuals with FXS or FXS with autism who have low cognitive abilities. Although individuals with comorbid FXS and autism may be, as a group, more impaired than those with only FXS, data from this small sample of males with comorbid FXS and autism with low IQs suggest that their relative strengths and weaknesses in spontaneous expressive language are largely comparable and not differentially affected by the context in which their talk occurs.

Biomarkers in the Study of Families of Individuals with Developmental Disabilities

Research during the past 20 years on families of children with developmental disabilities has yielded a rich body of knowledge about the stress of parenting a child with DD, and the risk and protective factors that result in profiles of family resilience vs. vulnerability at various stages of the family life course. Virtually all of this research has been based on data collected from self-report measures, and has focused on family interactions and relationships, and the psychosocial well-being of individual family members. The present chapter focuses on different sources of data, namely biomarkers, which have the potential to extend our understanding of the biological mechanisms by which the stress of parenting a child with developmental disabilities can take its toll on parents' physical and mental health. We focus on two examples: (1) variations in the FMR1 gene, FMRP, and FMR1 messenger RNA in mothers of children with fragile X syndrome and the association of these measures with maternal depression and anxiety; and (2) profiles of cortisol expression in mothers of children with disabilities and the association of cortisol with daily measures of caregiving stress.

Linkage and linkage disequilibrium scan for autism loci in an extended pedigree from Finland

Population isolates, such as Finland, have proved beneficial in mapping rare causative genetic variants due to a limited number of founders resulting in reduced genetic heterogeneity and extensive linkage disequilibrium (LD). We have here used this special opportunity to identify rare alleles in autism by genealogically tracing 20 autism families into one extended pedigree with verified genealogical links reaching back to the 17th century. In this unique pedigree, we performed a dense microsatellite marker genome-wide scan of linkage and LD and followed initial findings with extensive fine-mapping. We identified a putative autism susceptibility locus at 19p13.3 and obtained further evidence for previously identified loci at 1q23 and 15q11-q13. Most promising candidate genes were TLE2 and TLE6 clustered at 19p13 and ATP1A2 at 1q23.

Autism spectrum disorder in fragile X syndrome: a longitudinal evaluation

The present study extends our previous work on characterizing the autistic behavior profile of boys with fragile X syndrome (FXS) who meet Diagnostic and Statistical Manual for Mental Disorders, 4th Edition criteria for autism spectrum disorder (ASD) into a longitudinal evaluation of ASD in FXS (FXS + ASD). Specifically, we aimed to determine the stability of the diagnosis and profile of ASD in FXS over time. Through regression models, we also evaluated which autistic and social behaviors and skills were correlates of diagnosis and autistic behavior severity (i.e., Autism Diagnostic Interview-Revised total scores). Finally, we assessed the evolution of cognitive parameters in FXS + ASD. A population of 56 boys (30-88 months at baseline) with FXS was evaluated using measures of autistic, social, and cognitive behaviors and skills at three yearly evaluations. We found that the diagnosis of ASD in FXS was relatively stable over time. Further emphasizing this stability, we found a set of behaviors and skills, particularly those related to peer relationships and adaptive socialization, that differentiated FXS + ASD from the rest of the FXS cohort (FXS + None) and contributed to autistic severity at all time points. Nevertheless, the general improvement in autistic behavior observed in FXS + ASD coupled with the concurrent worsening in FXS + None resulted in less differentiation between the groups over time. Surprisingly, FXS + ASD IQ scores were stable while FXS + None non-verbal IQ scores declined. Our findings indicate that ASD is a distinctive subphenotype in FXS characterized by deficits in complex social interaction, with similarities to ASD in the general population.

Brain function and gaze fixation during facial-emotion processing in fragile X and autism

Fragile X syndrome (FXS) is the most commonly known genetic disorder associated with autism spectrum disorder (ASD). Overlapping features in these populations include gaze aversion, communication deficits, and social withdrawal. Although the association between FXS and ASD has been well documented at the behavioral level, the underlying neural mechanisms associated with the social/emotional deficits in these groups remain unclear. We collected functional brain images and eye-gaze fixations from 9 individuals with FXS and 14 individuals with idiopathic ASD, as well as 15 typically developing (TD) individuals, while they performed a facial-emotion discrimination task. The FXS group showed a similar yet less aberrant pattern of gaze fixations compared with the ASD group. The FXS group also showed fusiform gyrus (FG) hypoactivation compared with the TD control group. Activation in FG was strongly and positively associated with average eye fixation and negatively associated with ASD characteristics in the FXS group. The FXS group displayed significantly greater activation than both the TD control and ASD groups in the left hippocampus (HIPP), left superior temporal gyrus (STG), right insula (INS), and left postcentral gyrus (PCG). These group differences in brain activation are important as they suggest unique underlying face-processing neural circuitry in FXS versus idiopathic ASD, largely supporting the hypothesis that ASD characteristics in FXS and idiopathic ASD reflect partially divergent impairments at the neural level, at least in FXS individuals without a co-morbid diagnosis of ASD.

Language Development in Individuals with Fragile X Syndrome

Fragile X syndrome (FXS) is the leading inherited cause of intellectual disability. The syndrome is caused by a single gene mutation on the X chromosome. Although individual differences are large, most individuals with FXS display weaknesses across all language and literacy domains compared to peers of the same chronological age with typical cognitive and language development. Expressive, receptive, and pragmatic language abilities as well as literacy skills are similar to those of younger, typically developing peers at similar cognitive and language developmental levels, although there are areas in which impairments exceed developmental-level expectations. One area of special impairment is the higher occurrence of repetition in the language of individuals with FXS compared to developmentally matched peers. In this paper, we review the behavioral, language, and literacy characteristics of individuals with FXS and discuss potential clinical implications.

Associations between repetitive questioning, resistance to change, temper outbursts and anxiety in Prader-Willi and Fragile-X syndromes

BACKGROUND

The behavioural phenotypes of Prader-Willi (PWS) and Fragile-X (FraX) syndromes both comprise repetitive behaviours with differences between the profiles. In this study we investigated the context and antecedents to the repetitive behaviours and the association with other behavioural phenotypic characteristics in order to generate testable hypotheses regarding the cause of the behaviours.

METHOD

The parents or carers of 46 children with PWS (mean age 14.1 years; 20 girls), and 33 boys with FraX (mean age 13.11 years) were interviewed about their children's repetitive behaviour in a semi-structured format.

RESULTS

Children showed negative emotional behaviour (PWS: 87.0%; FraX: 79.4%) and repetitive questions (PWS: 78.3%; FraX: 73.5%) following changes in routine or expectations. Significantly more temper outbursts were reported to follow changes in children with PWS (89.1%) compared with boys with FraX (41.2%) (chi(2) = 20.93; P < 0.001). Anxiety that was frequently associated with repetitive and self-injurious behaviours in boys with FraX, followed changes in significantly more boys with FraX (76.5%) compared with children with PWS (6.5%) (chi(2) = 43.19, P < 0.001).

DISCUSSION

On the basis of these reports and existing literature, we hypothesise that decreases in predictability are aversive to children with PWS and FraX. We also hypothesise that these children have a propensity to show a syndrome-related pattern of behaviour (temper outbursts in PWS and displays of anxiety in FraX) when an event in the environment has this aversive property. We hypothesise that questions may be reinforcing to children in their own right by increasing the predictability of the environment. We outline how a specific cognitive deficit in the endophenotypes associated with both PWS and FraX could be investigated as a potential explanation for the hypothesised aversive properties of decreased predictability.

Psychiatric phenotypes associated with neurogenetic disorders

Advances in understanding the human genome and clinical application have led to identification of genetically based disorders that have distinctive behavioral phenotypes and risk for serious psychiatric disorders. Some patients have unrecognized genetic disorders presenting as psychiatric symptoms. Practitioners must be knowledgeable about the association between symptoms and underlying genetic bases. Treatment of neurogenetic disorders includes providing information about causes and prognoses. Patients are served best if they remain long term with a multidisciplinary team of providers who recognize the realities of a lifetime course, the high risk for symptom recurrence, and the need for providing information and support to families and coordinating medical and psychiatric care.

Autism profiles of males with fragile X syndrome

Autism, which is common in individuals with fragile X syndrome, is often difficult to diagnose. We compared the diagnostic classifications of two measures for autism diagnosis, the ADOS and the ADI-R, in addition to the DSM-IV-TR in 63 males with this syndrome. Overall, 30% of the subjects met criteria for autistic disorder and 30% met criteria for PDD-NOS. The classifications on the ADOS and DSM-IV-TR were most similar, whereas the ADI-R classified subjects as autistic much more frequently. We further investigated the relationship of both FMRP and FMRI mRNA to symptoms of autism in this cohort and found no significant relationship between the measures of autism and molecular features, including FMRP, FMRI mRNA, and CGG repeat number.

Autism profiles of males with fragile X syndrome

Autism, which is common in individuals with fragile X syndrome, is often difficult to diagnose. We compared the diagnostic classifications of two measures for autism diagnosis, the ADOS and the ADI-R, in addition to the DSM-IV-TR in 63 males with this syndrome. Overall, 30% of the subjects met criteria for autistic disorder and 30% met criteria for PDD-NOS. The classifications on the ADOS and DSM-IV-TR were most similar, whereas the ADI-R classified subjects as autistic much more frequently. We further investigated the relationship of both FMRP and FMRI mRNA to symptoms of autism in this cohort and found no significant relationship between the measures of autism and molecular features, including FMRP, FMRI mRNA, and CGG repeat number.

Recognizing the role of parents in developmental outcomes: a systems approach to evaluating the child with developmental disabilities

When developmental concerns arise in children, a clinical assessment focuses on the child's developmental profile to achieve three goals (1) determine diagnosis, (2) develop interventions, and (3) evaluate progress. Parents often have needs during this time that are not addressed by professionals because of the exclusive focus on the child during the evaluation. In this article, we suggest that clinicians take a "systems" approach to the assessment process by recognizing how the well being of family members can impact a child with a developmental disability. We review systems theory and its conceptualization of individual functioning and discuss how parental well-being differs according to child diagnosis. Finally we suggest a systems-based model to use during the assessment process.

Social phenotypes in neurogenetic syndromes

Many of the known genetically based neurodevelopmental disorders are associated with a distinctive behavioral phenotype. As these behavioral phenotypes have been elucidated by clinical research, distinctive profiles of social traits have emerged as prominent syndromic features. This article reviews social phenotypic findings for fragile X syndrome, Down syndrome, Prader-Willi syndrome, Smith-Magenis syndrome, Turner syndrome, Williams syndrome, and velocardiofacial syndrome. An analysis of these social profiles raises several questions regarding the relationship between identified social impairments and autism and the relationship between social impairments in neurodevelopmental disorders and those found in normative child populations. The unique profile of certain of the known behavioral phenotypes also serves to distinguish several dimensions of sociability that are not readily observed in typical populations.

Autism spectrum phenotype in males and females with fragile X full mutation and premutation

The behavioural phenotype of autism was assessed in individuals with full mutation and premutation fragile X syndrome (FXS) using the Autism Diagnostic Observation Scale-Generic (ADOS-G) and the Autism Diagnostic Interview (ADI-R). The participants, aged 5-80 years, comprised 33 males and 31 females with full mutation, 7 males and 43 females with premutation, and 38 non-fragile X relatives (29 males, 9 females). In the full mutation group, a total of 67% males and 23% females met either the Autism Disorder (AD) or the Autism Spectrum Disorder (ASD) criteria on at least one of the diagnostic tests. In the premutation group, 14% males and 5% females met the ADOS-G criteria for ASD. The presence of autism manifestations in males and females with full mutation and premutation provide support for a spectrum view.

A preliminary study of screening for risk of autism in children with fragile X syndrome: testing two risk cut-offs for the Checklist for Autism in Toddlers

OBJECTIVE

Risk criteria for the Checklist for Autism in Toddlers (CHAT) and modified risk criteria (i.e. the Denver Criteria) were compared in a group of children with fragile X syndrome (FXS) and autism.

METHOD

Participants were 17 children aged 2-4 years with DNA confirmation of FXS. Four children had autism and 13 children did not.

RESULTS

Preliminary findings regarding the sensitivity and specificity of the CHAT for detecting risk for autism in children with FXS are as follows: using the original CHAT risk criteria, sensitivity and specificity were 50% and 100%, respectively; and using the Denver Criteria, sensitivity and specificity were 75% and 92%, respectively.

CONCLUSIONS

The CHAT and the Denver Criteria resulted in preliminary findings suggesting high levels of sensitivity to autism in children with FXS.

Language development and fragile X syndrome: profiles, syndrome-specificity, and within-syndrome differences

Fragile X syndrome (FXS) is the leading inherited cause of mental retardation. In this article, we review what is known about the language and related problems of individuals with FXS. In doing so, we focus on the syndrome-specific features of the language phenotype and on the organismic (i.e., genetic and individual neurocognitive and behavioral) and environmental factors associated with within-syndrome variation in the phenotype. We also briefly review those aspects of the behavioral phenotype of FXS that are relevant for understanding syndrome-specific features of, and within-syndrome variability in, language. The review includes summaries of research on the prelinguistic foundations for language development and on each of the major components of language (i.e., vocabulary, morphosyntax, and pragmatics). Throughout the review, we point out implications of existing research for intervention as well as directions for future research.

Fragile X syndrome and autism at the intersection of genetic and neural networks

Autism, an entirely behavioral diagnosis with no largely understood etiologies and no population-wide biomarkers, contrasts with fragile X syndrome (FXS), a single-gene disorder with definite alterations of gene expression and neuronal morphology. Nevertheless, the behavioral overlap between autism and FXS suggests some overlapping mechanisms. Understanding how the single-gene alteration in FXS plays out within complex genetic and neural network processes may suggest targets for autism research and illustrate strategies for relating autism to more singular genetic syndromes.

Autistic behavior in children with fragile X syndrome: prevalence, stability, and the impact of FMRP

We examined autistic behavior in a cross-sectional sample of 179 children with fragile X syndrome (FXS) and a longitudinal subset of 116 children using the Childhood Autism Rating Scale (CARS) to (a) determine a prevalence of autistic behavior in FXS, (b) examine the stability of autistic ratings over time, and (c) assess the association between the fragile X mental retardation protein (FMRP) and autistic behavior. Approximately 21% of the sample of 129 children (25.9% of boys) scored at or above the cutoff for autism. CARS scores increased slowly, yet significantly, over time, and low levels of FMRP were associated with higher mean levels of autistic behavior as measured by the CARS.

Autism spectrum disorder in Fragile X syndrome: differential contribution of adaptive socialization and social withdrawal

The present study extends our previous work on characterizing the profile of social behavior abnormalities in boys with Fragile X (FraX) and autism spectrum disorder (ASD) using clinically oriented behavioral rating scales and standardized instruments. The goal was to further distinguish behavioral parameters contributing to the diagnostic classification of FraX + ASD. The study design included two cohorts of boys with FraX (3-8 years), a larger main cohort for cross-sectional analyses (n = 56, 24 with ASD), and a longitudinal subset (n = 30, 11 with ASD) of the main cohort with up to 3 yearly observations. The focus was on the relative contribution of delayed adaptive socialization and social withdrawal, including item components of their corresponding rating instruments, to the diagnosis of ASD in boys with FraX. Using a combination of regression analyses, we demonstrated that: (1) as delayed socialization, social withdrawal is also a correlate of FraX + ASD; (2) items of social withdrawal scales representing avoidance were the main predictors of ASD status, particularly in older boys; (3) adaptive socialization skills reflecting rules of social behavior and recognition and labeling of emotions, linked to verbal reasoning abilities, were selectively associated with FraX + ASD; (4) adaptive socialization is the primary determinant over time of ASD status in boys with FraX; and (5) integrated adaptive socialization-social withdrawal models allow the identification of distinctive FraX + ASD subgroups. Altogether, our findings suggest that two distinct but interrelated social behavior abnormalities, one linked to impaired cognitive processes (delayed socialization) and the second one to disturbance in limbic circuits (avoidance), play a role in the development of ASD in boys with FraX.