Morphometric spatial patterns differentiating boys with fragile X syndrome, typically developing boys, and developmentally delayed boys aged 1 to 3 years

Oligodendroglia and myelin pathology in fragile X syndrome

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

TRRAP-mediated acetylation on Sp1 regulates adult neurogenesis

The adult hippocampal neurogenesis plays a vital role in the function of the central nervous system (CNS), including memory consolidation, cognitive flexibility, emotional function, and social behavior. The deficiency of adult neural stem cells (aNSCs) in maintaining the quiescence and entering cell cycle, self-renewal and differentiation capacity is detrimental to the functional integrity of neurons and cognition of the adult brain. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) have been shown to modulate brain functionality and are important for embryonic neurogenesis via regulation of gene transcription. We showed previously that Trrap, an adapter for several HAT complexes, is required for Sp1 transcriptional control of the microtubule dynamics in neuronal cells. Here, we find that Trrap deletion compromises self-renewal and differentiation of aNSCs in mice and in cultures. We find that the acetylation status of lysine residues K16, K19, K703 and K639 all fail to overcome Trrap-deficiency-incurred instability of Sp1, indicating a scaffold role of Trrap. Interestingly, the deacetylation of Sp1 at K639 and K703 greatly increases Sp1 binding to the promoter of target genes, which antagonizes Trrap binding, and thereby elevates Sp1 activity. However, only deacetylated K639 is refractory to Trrap deficiency and corrects the differentiation defects of Trrap-deleted aNSCs. We demonstrate that the acetylation pattern at K639 by HATs dictates the role of Sp1 in the regulation of adult neurogenesis.

Cortical Source Analysis of the Face Sensitive N290 ERP Component in Infants at High Risk for Autism

Appropriate head models for cortical source analysis were investigated and applied to source analyses examining the neural bases of the face-sensitive N290 event-related potential (ERP) component in infants at high risk for autism spectrum disorder (ASD). This included infant siblings of children with ASD (ASIBs) and infants with fragile X syndrome (FXS). First, alternative head models for use with ASIBs and FXS were investigated. Head models created from the infant's own MRI were examined in relation to five head models based on average MRI templates. The results of the head model comparison identified group-specific (i.e., ASIB or FXS) head models created from a large collection of structural MRIs as the best substitution for the head model created from the participant's own structural MRI. Second, the cortical source analysis was completed on N290 data collected from a previous study to investigate brain areas associated with face sensitive ERP responses. Participants' own MRIs were used for head models when available, and the group-specific head model was used when the participants' own MRIs were not available. The results provide evidence for unique patterns of neural activation during face processing across infants at high and low risk for ASD and across etiologically distinct high-risk groups. All infants demonstrated greater activation to faces than toys in brain areas most associated with specialized face processing. Infants with FXS displayed higher levels of activation to faces across all areas analyzed, while ASIBs show more muted levels of activation. Overall, the results of the current study demonstrate the importance of group-specific head models for accurate cortical source analysis in infants at high risk for ASD. This also allows for further research on early distinctions in brain function based on risk status.

Grey and white matter volumes in early childhood: A comparison of voxel-based morphometry pipelines

Early childhood is an important period of sensory, motor, cognitive and socio-emotional maturation, yet relatively little is known about the brain changes specific to this period. Voxel-based morphometry (VBM) is a technique to estimate regional brain volumes from magnetic resonance (MR) images. The default VBM processing pipeline can be customized to increase accuracy of segmentation and normalization, yet the impact of customizations on analyses in young children are not clear. Here, we assessed the impact of different preprocessing steps on T1-weighted MR images from typically developing children in two separate cohorts. Data were processed with the Computational Anatomy Toolbox (CAT12), using seven different VBM pipelines with distinct combinations of tissue probability maps (TPMs) and DARTEL templates created using the Template-O-Matic, and CerebroMatic. The first cohort comprised female children aged 3.9-7.9 years (N = 62) and the second included boys and girls aged 2.7-8 years (N = 74). We found that pipelines differed significantly in their tendency to classify voxels as grey or white matter and the conclusions about some age effects were pipeline-dependent. Our study helps to both understand age-associations in grey and white matter volume across early childhood and elucidate the impact of VBM customization on brain volumes in this age range.

Reduced axonal caliber and structural changes in a rat model of Fragile X syndrome with a deletion of a K-Homology domain of Fmr1

Fragile X syndrome (FXS) is a neurodevelopmental disorder that is caused by mutations in the FMR1 gene. Neuroanatomical alterations have been reported in both male and female individuals with FXS, yet the morphological underpinnings of these alterations have not been elucidated. In the current study, we found structural changes in both male and female rats that model FXS, some of which are similarly impaired in both sexes, including the superior colliculus and periaqueductal gray, and others that show sex-specific changes. The splenium of the corpus callosum, for example, was only impaired in males. We also found reduced axonal caliber in the splenium, offering a mechanism for its structural changes. Furthermore, we found that overall, male rats have higher brain-wide diffusion than female rats. Our results provide insight into which brain regions are vulnerable to a loss of Fmr1 expression and reveal an impairment at the level of the axon that could cause structural changes in white matter regions.

Developmental studies in fragile X syndrome

Fragile X syndrome (FXS) is the most common single gene cause of autism and intellectual disabilities. Humans with FXS exhibit increased anxiety, sensory hypersensitivity, seizures, repetitive behaviors, cognitive inflexibility, and social behavioral impairments. The main purpose of this review is to summarize developmental studies of FXS in humans and in the mouse model, the Fmr1 knockout mouse. The literature presents considerable evidence that a number of early developmental deficits can be identified and that these early deficits chart a course of altered developmental experience leading to symptoms well characterized in adolescents and adults. Nevertheless, a number of critical issues remain unclear or untested regarding the development of symptomology and underlying mechanisms. First, what is the role of FMRP, the protein product of Fmr1 gene, during different developmental ages? Does the absence of FMRP during early development lead to irreversible changes, or could reintroduction of FMRP or therapeutics aimed at FMRP-interacting proteins/pathways hold promise when provided in adults? These questions have implications for clinical trial designs in terms of optimal treatment windows, but few studies have systematically addressed these issues in preclinical and clinical work. Published studies also point to complex trajectories of symptom development, leading to the conclusion that single developmental time point studies are unlikely to disambiguate effects of genetic mutation from effects of altered developmental experience and compensatory plasticity. We conclude by suggesting a number of experiments needed to address these major gaps in the field.

Executive Function in Fragile X Syndrome: A Systematic Review

Executive function (EF) supports goal-directed behavior and includes key aspects such as working memory, inhibitory control, cognitive flexibility, attention, processing speed, and planning. Fragile X syndrome (FXS) is the leading inherited monogenic cause of intellectual disability and is phenotypically characterized by EF deficits beyond what is expected given general cognitive impairments. Yet, a systematic review of behavioral studies using performance-based measures is needed to provide a summary of EF deficits across domains in males and females with FXS, discuss clinical and biological correlates of these EF deficits, identify critical limitations in available research, and offer suggestions for future studies in this area. Ultimately, this review aims to advance our understanding of the underlying pathophysiological mechanisms contributing to EF in FXS and to inform the development of outcome measures of EF and identification of new treatment targets in FXS.

Neuroanatomical abnormalities in fragile X syndrome during the adolescent and young adult years

Abnormal brain development and cognitive dysfunction have been reported both in children and in adults with fragile X syndrome (FXS). However, few studies have examined neuroanatomical abnormalities in FXS during adolescence. In this study we focus on adolescent subjects with FXS (N = 54) as compared to age- and sex-matched subjects with idiopathic intellectual disability (Comparison Group) (N = 32), to examine neuroanatomical differences during this developmental period. Brain structure was assessed with voxel-based morphometry and independent groups t-test in SPM8 software. Results showed that the FXS group, relative to the comparison group, had significantly larger gray matter volume (GMV) in only one region: the bilateral caudate nucleus, but have smaller GMV in several regions including bilateral medial frontal, pregenual cingulate, gyrus rectus, insula, and superior temporal gyrus. Group differences also were noted in white matter regions. Within the FXS group, lower FMRP levels were associated with less GMV in several regions including cerebellum and gyrus rectus, and less white matter volume (WMV) in pregenual cingulate, middle frontal gyrus, and other regions. Lower full scale IQ within the FXS group was associated with larger right caudate nucleus GMV. In conclusion, adolescents and young adults with FXS demonstrate neuroanatomical abnormalities consistent with those previously reported in children and adults with FXS. These brain variations likely result from reduced FMRP during early neurodevelopment and mediate downstream deleterious effects on cognitive function.

Developmental trajectories of executive functions in young males with fragile X syndrome

BACKGROUND

Executive functions (EF) have been identified as impaired in FXS, but few studies have examined their developmental trajectories.

AIMS

The primary aim of this longitudinal study was to examine the development of EF in young males with FXS compared to Mental Age (MA)-matched controls.

METHODS AND PROCEDURES

The sample comprised 56 boys with FXS (ages 7-13 years), and 48 MA-matched typical boys (ages 4-8 years). EF tasks included measures of inhibitory control, working memory, cognitive flexibility/set-shifting, problem solving/planning, and processing speed. Tasks were administered at three time points over five-years.

OUTCOMES AND RESULTS

The MA-Matched Typical boys significantly outperformed the FXS boys on all EF tasks, with the FXS Group showing a pattern of slow, but positive growth on most EF tasks. For working memory tasks, significant interactions were noted between MA and autism symptom severity, and MA and medication status. The probability of task completion increased with higher MA.

CONCLUSIONS AND IMPLICATIONS

These findings contribute to our understanding of the development of EF in this population. They also lay the foundation for use of EF tasks in treatment efforts, particularly with respect to documenting improvements and practice effects, and in understanding associations with targeted developmental outcomes.

Development of White Matter Circuitry in Infants With Fragile X Syndrome

IMPORTANCE

Fragile X syndrome (FXS) is a genetic neurodevelopmental disorder and the most common inherited cause of intellectual disability in males. However, there are no published data on brain development in children with FXS during infancy.

OBJECTIVE

To characterize the development of white matter at ages 6, 12, and 24 months in infants with FXS compared with that of typically developing controls.

DESIGN, SETTING, AND PARTICIPANTS

Longitudinal behavioral and brain imaging data were collected at 1 or more time points from 27 infants with FXS and 73 typically developing controls between August 1, 2008, and June 14, 2016, at 2 academic medical centers. Infants in the control group had no first- or second-degree relatives with intellectual or psychiatric disorders, including FXS and autism spectrum disorder.

MAIN OUTCOMES AND MEASURES

Nineteen major white matter pathways were defined in common atlas space based on anatomically informed methods. Diffusion parameters, including fractional anisotropy, were compared between groups using linear mixed effects modeling. Fiber pathways showing group differences were subsequently examined in association with direct measures of verbal and nonverbal development.

RESULTS

There were significant differences in the development of 12 of 19 fiber tracts between the 27 infants with FXS (22 boys and 5 girls) and the 73 infants in the control group (46 boys and 27 girls), with lower fractional anisotropy in bilateral subcortical-frontal, occipital-temporal, temporal-frontal, and cerebellar-thalamic pathways, as well as 4 of 6 subdivisions of the corpus callosum. For all 12 of these pathways, there were significant main effects between groups but not for the interaction of age × group, indicating that lower fractional anisotropy was present and stable from age 6 months in infants with FXS. Lower fractional anisotropy values in the uncinate fasciculi were correlated with lower nonverbal developmental quotient in the FXS group (left uncinate, F = 10.06; false discovery rate-corrected P = .03; right uncinate, F = 21.8; P = .004).

CONCLUSIONS AND RELEVANCE

The results substantiate in human infants the essential role of fragile X gene expression in the early development of white matter. The findings also suggest that the neurodevelopmental effects of FXS are well established at 6 months of age.

Intelligence and specific cognitive functions in intellectual disability: implications for assessment and classification

PURPOSE OF REVIEW

Current diagnostic criteria for intellectual disability categorize ability as measured by IQ tests. However, this does not suit the new conceptualization of intellectual disability, which refers to a range of neuropsychiatric syndromes that have in common early onset, cognitive impairments, and consequent deficits in learning and adaptive functioning. A literature review was undertaken on the concept of intelligence and whether it encompasses a range of specific cognitive functions to solve problems, which might be better reported as a profile, instead of an IQ, with implications for diagnosis and classification of intellectual disability.

RECENT FINDINGS

Data support a model of intelligence consisting of distinct but related processes. Persons with intellectual disability with the same IQ level have different cognitive profiles, based on varying factors involved in aetiopathogenesis. Limitations of functioning and many biopsychological factors associated with intellectual disability are more highly correlated with impairments of specific cognitive functions than with overall IQ.

SUMMARY

The current model of intelligence, based on IQ, is of limited utility for intellectual disability, given the wide range and variability of cognitive functions and adaptive capacities. Assessing level of individual impairment in executive and specific cognitive functions may be a more useful alternative. This has considerable implications for the revision of the International Classification of Diseases and for the cultural attitude towards intellectual disability in general.

Fragile X syndrome

Fragile X syndrome (FXS) is the leading inherited form of intellectual disability and autism spectrum disorder, and patients can present with severe behavioural alterations, including hyperactivity, impulsivity and anxiety, in addition to poor language development and seizures. FXS is a trinucleotide repeat disorder, in which >200 repeats of the CGG motif in FMR1 leads to silencing of the gene and the consequent loss of its product, fragile X mental retardation 1 protein (FMRP). FMRP has a central role in gene expression and regulates the translation of potentially hundreds of mRNAs, many of which are involved in the development and maintenance of neuronal synaptic connections. Indeed, disturbances in neuroplasticity is a key finding in FXS animal models, and an imbalance in inhibitory and excitatory neuronal circuits is believed to underlie many of the clinical manifestations of this disorder. Our knowledge of the proteins that are regulated by FMRP is rapidly growing, and this has led to the identification of multiple targets for therapeutic intervention, some of which have already moved into clinical trials or clinical practice.

Longitudinal identification of clinically distinct neurophenotypes in young children with fragile X syndrome

Fragile X syndrome (FXS), due to mutations of the FMR1 gene, is the most common known inherited cause of developmental disability. The cognitive, behavioral, and neurological phenotypes observed in affected individuals can vary considerably, making it difficult to predict outcomes and determine the need for interventions. We sought to examine early structural brain growth as a potential marker for identification of clinically meaningful subgroups. Participants included 42 very young boys with FXS who completed a T1-weighted anatomical MRI and cognitive/behavioral assessment at two longitudinal time points, with mean ages of 2.89 y and 4.91 y. Topological data analysis (TDA), an unsupervised approach to multivariate pattern analysis, was applied to the longitudinal anatomical data to identify coherent but heretofore unknown subgroups. TDA revealed two large subgroups within the study population based solely on longitudinal MRI data. Post hoc comparisons of cognition, adaptive functioning, and autism severity scores between these groups demonstrated that one group was consistently higher functioning on all measures at both time points, with pronounced and significant unidirectional differences (P < 0.05 for time point 1 and/or time point 2 for each measure). These results support the existence of two longitudinally defined, neuroanatomically distinct, and clinically relevant phenotypes among boys with FXS. If confirmed by additional analyses, such information may be used to predict outcomes and guide design of targeted therapies. Furthermore, TDA of longitudinal anatomical MRI data may represent a useful method for reliably and objectively defining subtypes within other neuropsychiatric disorders.

Imaging genetics in neurodevelopmental psychopathology

Neurodevelopmental disorders are defined by highly heritable problems during development and brain growth. Attention-deficit/hyperactivity disorder (ADHD), autism spectrum disorders (ASDs), and intellectual disability (ID) are frequent neurodevelopmental disorders, with common comorbidity among them. Imaging genetics studies on the role of disease-linked genetic variants on brain structure and function have been performed to unravel the etiology of these disorders. Here, we reviewed imaging genetics literature on these disorders attempting to understand the mechanisms of individual disorders and their clinical overlap. For ADHD and ASD, we selected replicated candidate genes implicated through common genetic variants. For ID, which is mainly caused by rare variants, we included genes for relatively frequent forms of ID occurring comorbid with ADHD or ASD. We reviewed case-control studies and studies of risk variants in healthy individuals. Imaging genetics studies for ADHD were retrieved for SLC6A3/DAT1, DRD2, DRD4, NOS1, and SLC6A4/5HTT. For ASD, studies on CNTNAP2, MET, OXTR, and SLC6A4/5HTT were found. For ID, we reviewed the genes FMR1, TSC1 and TSC2, NF1, and MECP2. Alterations in brain volume, activity, and connectivity were observed. Several findings were consistent across studies, implicating, for example, SLC6A4/5HTT in brain activation and functional connectivity related to emotion regulation. However, many studies had small sample sizes, and hypothesis-based, brain region-specific studies were common. Results from available studies confirm that imaging genetics can provide insight into the link between genes, disease-related behavior, and the brain. However, the field is still in its early stages, and conclusions about shared mechanisms cannot yet be drawn.

Public Health Literature Review of Fragile X Syndrome

OBJECTIVES

The purpose of this systematic literature review is to describe what is known about fragile X syndrome (FXS) and to identify research gaps. The results can be used to help inform future public health research and provide pediatricians with up-to-date information about the implications of the condition for individuals and their families.

METHODS

An electronic literature search was conducted, guided by a variety of key words. The search focused on 4 areas of both clinical and public health importance: (1) the full mutation phenotype, (2) developmental trajectories across the life span, (3) available interventions and treatments, and (4) impact on the family. A total of 661 articles were examined and 203 were included in the review.

RESULTS

The information is presented in the following categories: developmental profile (cognition, language, functional skills, and transition to adulthood), social-emotional profile (cooccurring psychiatric conditions and behavior problems), medical profile (physical features, seizures, sleep, health problems, and physiologic features), treatment and interventions (educational/behavioral, allied health services, and pharmacologic), and impact on the family (family environment and financial impact). Research gaps also are presented.

CONCLUSIONS

The identification and treatment of FXS remains an important public health and clinical concern. The information presented in this article provides a more robust understanding of FXS and the impact of this complex condition for pediatricians. Despite a wealth of information about the condition, much work remains to fully support affected individuals and their families.

Cellular distribution of the fragile X mental retardation protein in the mouse brain

The fragile X mental retardation protein (FMRP) plays an important role in normal brain development. Absence of FMRP results in abnormal neuronal morphologies in a selected manner throughout the brain, leading to intellectual deficits and sensory dysfunction in the fragile X syndrome (FXS). Despite FMRP importance for proper brain function, its overall expression pattern in the mammalian brain at the resolution of individual neuronal cell groups is not known. In this study we used FMR1 knockout and isogenic wildtype mice to systematically map the distribution of FMRP expression in the entire mouse brain. Using immunocytochemistry and cellular quantification analyses, we identified a large number of prominent cell groups expressing high levels of FMRP at the subcortical levels, in particular sensory and motor neurons in the brainstem and thalamus. In contrast, many cell groups in the midbrain and hypothalamus exhibit low FMRP levels. More important, we describe differential patterns of FMRP distribution in both cortical and subcortical brain regions. Almost all major brain areas contain high and low levels of FMRP cell groups adjacent to each other or between layers of the same cortical areas. These differential patterns indicate that FMRP expression appears to be specific to individual neuronal cell groups instead of being associated with all neurons in distinct brain regions, as previously considered. Taken together, these findings support the notion of FMRP differential neuronal regulation and strongly implicate the contribution of fundamental sensory and motor processing at subcortical levels to FXS pathology. J. Comp. Neurol. 525:818-849, 2017. © 2016 Wiley Periodicals, Inc.

Anomalous gray matter patterns in specific reading comprehension deficit are independent of dyslexia

Specific reading comprehension deficit (SRCD) affects up to 10 % of all children. SRCD is distinct from dyslexia (DYS) in that individuals with SRCD show poor comprehension despite adequate decoding skills. Despite its prevalence and considerable behavioral research, there is not yet a unified cognitive profile of SRCD. While its neuroanatomical basis is unknown, SRCD could be anomalous in regions subserving their commonly reported cognitive weaknesses in semantic processing or executive function. Here we investigated, for the first time, patterns of gray matter volume difference in SRCD as compared to DYS and typical developing (TD) adolescent readers (N = 41). A linear support vector machine algorithm was applied to whole brain gray matter volumes generated through voxel-based morphometry. As expected, DYS differed significantly from TD in a pattern that included features from left fusiform and supramarginal gyri (DYS vs. TD: 80.0 %, p < 0.01). SRCD was well differentiated not only from TD (92.5 %, p < 0.001) but also from DYS (88.0 %, p < 0.001). Of particular interest were findings of reduced gray matter volume in right frontal areas that were also supported by univariate analysis. These areas are thought to subserve executive processes relevant for reading, such as monitoring and manipulating mental representations. Thus, preliminary analyses suggest that SRCD readers possess a distinct neural profile compared to both TD and DYS readers and that these differences might be linked to domain-general abilities. This work provides a foundation for further investigation into variants of reading disability beyond DYS.

Female-Specific Intergenerational Transmission Patterns of the Human Corticolimbic Circuitry

Parents have large genetic and environmental influences on offspring's cognition, behavior, and brain. These intergenerational effects are observed in mood disorders, with particularly robust association in depression between mothers and daughters. No studies have thus far examined the neural bases of these intergenerational effects in humans. Corticolimbic circuitry is known to be highly relevant in a wide range of processes, including mood regulation and depression. These findings suggest that corticolimbic circuitry may also show matrilineal transmission patterns. Therefore, we examined human parent-offspring association in this neurocircuitry and investigated the degree of association in gray matter volume between parent and offspring. We used voxelwise correlation analysis in a total of 35 healthy families, consisting of parents and their biological offspring. We found positive associations of regional gray matter volume in the corticolimbic circuit, including the amygdala, hippocampus, anterior cingulate cortex, and ventromedial prefrontal cortex between biological mothers and daughters. This association was significantly greater than mother-son, father-daughter, and father-son associations. The current study suggests that the corticolimbic circuitry, which has been implicated in mood regulation, shows a matrilineal-specific transmission patterns. Our preliminary findings are consistent with what has been found behaviorally in depression and may have clinical implications for disorders known to have dysfunction in mood regulation such as depression. Studies such as ours will likely bridge animal work examining gene expression in the brains and clinical symptom-based observations and provide promising ways to investigate intergenerational transmission patterns in the human brain.

SIGNIFICANCE STATEMENT

Parents have large genetic and environmental influences on the offspring, known as intergenerational effects. Specifically, depression has been shown to exhibit strong matrilineal transmission patterns. Although intergenerational transmission patterns in the human brain are virtually unknown, this would suggest that the corticolimbic circuitry relevant to a wide range of processes including mood regulation may also show matrilineal transmission patterns. Therefore, we examined the degree of association in corticolimbic gray matter volume (GMV) between parent and offspring in 35 healthy families. We found that positive correlations in maternal corticolimbic GMV with daughters were significantly greater than other parent-offspring dyads. Our findings provide new insight into the potential neuroanatomical basis of circuit-based female-specific intergenerational transmission patterns in depression.

Early Behavioral Abnormalities and Perinatal Alterations of PTEN/AKT Pathway in Valproic Acid Autism Model Mice

Exposure to valproic acid (VPA) during pregnancy has been linked with increased incidence of autism, and has repeatedly been demonstrated as a useful autism mouse model. We examined the early behavioral and anatomical changes as well as molecular changes in mice prenatally exposed to VPA (VPA mice). In this study, we first showed that VPA mice showed developmental delays as assessed with self-righting, eye opening tests and impaired social recognition. In addition, we provide the first evidence that primary cultured neurons from VPA-treated embryos present an increase in dendritic spines, compared with those from control mice. Mutations in phosphatase and tensin homolog (PTEN) gene are also known to be associated with autism, and mice with PTEN knockout show autistic characteristics. Protein expression of PTEN was decreased and the ratio of p-AKT/AKT was increased in the cerebral cortex and the hippocampus, and a distinctive anatomical change in the CA1 region of the hippocampus was observed. Taken together, our study suggests that prenatal exposure to VPA induces developmental delays and neuroanatomical changes via the reduction of PTEN level and these changes were detectable in the early days of life.

HPA axis function predicts development of working memory in boys with FXS

The present study examines verbal working memory over time in boys with fragile X syndrome (FXS) compared to nonverbal mental-age (NVMA) matched, typically developing (TD) boys. Concomitantly, the relationship between cortisol-a physiological marker for stress-and verbal working memory performance over time is examined to understand the role of physiological mechanisms in cognitive development in FXS. Participants were assessed between one and three times over a 2-year time frame using two verbal working memory tests that differ in complexity: memory for words and auditory working memory with salivary cortisol collected at the beginning and end of each assessment. Multilevel modeling results indicate specific deficits over time on the memory for words task in boys with FXS compared to TD controls that is exacerbated by elevated baseline cortisol. Similar increasing rates of growth over time were observed for boys with FXS and TD controls on the more complex auditory working memory task, but only boys with FXS displayed an association of increased baseline cortisol and lower performance. This study highlights the benefit of investigations of how dynamic biological and cognitive factors interact and influence cognitive development over time.

Multivariate analyses applied to fetal, neonatal and pediatric MRI of neurodevelopmental disorders

Multivariate analysis (MVA) is a class of statistical and pattern recognition methods that involve the processing of data that contains multiple measurements per sample. MVA can be used to address a wide variety of medical neuroimaging-related challenges including identifying variables associated with a measure of clinical importance (i.e. patient outcome), creating diagnostic tests, assisting in characterizing developmental disorders, understanding disease etiology, development and progression, assisting in treatment monitoring and much more. Compared to adults, imaging of developing immature brains has attracted less attention from MVA researchers. However, remarkable MVA research growth has occurred in recent years. This paper presents the results of a systematic review of the literature focusing on MVA technologies applied to neurodevelopmental disorders in fetal, neonatal and pediatric magnetic resonance imaging (MRI) of the brain. The goal of this manuscript is to provide a concise review of the state of the scientific literature on studies employing brain MRI and MVA in a pre-adult population. Neurological developmental disorders addressed in the MVA research contained in this review include autism spectrum disorder, attention deficit hyperactivity disorder, epilepsy, schizophrenia and more. While the results of this review demonstrate considerable interest from the scientific community in applications of MVA technologies in pediatric/neonatal/fetal brain MRI, the field is still young and considerable research growth remains ahead of us.

Childhood antecedents and risk for adult mental disorders

Progress in treating and preventing mental disorders may follow from research that integrates development, genetics, and neuroscience. This review first delineates how longitudinal research has identified three particular groups of disorders shown to differ on the basis of symptom trajectories and risk-factor profiles. In the next section, the review describes how research on genetic contributions to psychopathology has elucidated the nature of risk for two groups of disorders, the neurodevelopmental and psychotic disorders. In the third section, the review describes how research on environmental contributions to psychopathology has targeted early temperament, its associated perturbations in information-processing functions, and its relations to a third group of disorders, the emotional disorders. For all three groups of disorders, such integrative research has generated ideas about novel interventions. The hope is that over the coming decade such ideas will lead to novel treatments that alter the trajectory of risk in developmental psychopathology.

Estimating individual contribution from group-based structural correlation networks

Coordinated variations in brain morphology (e.g., cortical thickness) across individuals have been widely used to infer large-scale population brain networks. These structural correlation networks (SCNs) have been shown to reflect synchronized maturational changes in connected brain regions. Further, evidence suggests that SCNs, to some extent, reflect both anatomical and functional connectivity and hence provide a complementary measure of brain connectivity in addition to diffusion weighted networks and resting-state functional networks. Although widely used to study between-group differences in network properties, SCNs are inferred only at the group-level using brain morphology data from a set of participants, thereby not providing any knowledge regarding how the observed differences in SCNs are associated with individual behavioral, cognitive and disorder states. In the present study, we introduce two novel distance-based approaches to extract information regarding individual differences from the group-level SCNs. We applied the proposed approaches to a moderately large dataset (n=100) consisting of individuals with fragile X syndrome (FXS; n=50) and age-matched typically developing individuals (TD; n=50). We tested the stability of proposed approaches using permutation analysis. Lastly, to test the efficacy of our method, individual contributions extracted from the group-level SCNs were examined for associations with intelligence scores and genetic data. The extracted individual contributions were stable and were significantly related to both genetic and intelligence estimates, in both typically developing individuals and participants with FXS. We anticipate that the approaches developed in this work could be used as a putative biomarker for altered connectivity in individuals with neurodevelopmental disorders.

Mapping genetically controlled neural circuits of social behavior and visuo-motor integration by a preliminary examination of atypical deletions with Williams syndrome

In this study of eight rare atypical deletion cases with Williams-Beuren syndrome (WS; also known as 7q11.23 deletion syndrome) consisting of three different patterns of deletions, compared to typical WS and typically developing (TD) individuals, we show preliminary evidence of dissociable genetic contributions to brain structure and human cognition. Univariate and multivariate pattern classification results of morphometric brain patterns complemented by behavior implicate a possible role for the chromosomal region that includes: 1) GTF2I/GTF2IRD1 in visuo-spatial/motor integration, intraparietal as well as overall gray matter structures, 2) the region spanning ABHD11 through RFC2 including LIMK1, in social cognition, in particular approachability, as well as orbitofrontal, amygdala and fusiform anatomy, and 3) the regions including STX1A, and/or CYLN2 in overall white matter structure. This knowledge contributes to our understanding of the role of genetics on human brain structure, cognition and pathophysiology of altered cognition in WS. The current study builds on ongoing research designed to characterize the impact of multiple genes, gene-gene interactions and changes in gene expression on the human brain.

Alterations of visual and auditory evoked potentials in fragile X syndrome

BACKGROUND

Fragile X Syndrome (FXS) is the most common monogenic form of intellectual disability and one of the few known monogenic causes of autism. It is caused by a trinucleotide repeat expansion in the FMR1 ('Fragile X Mental Retardation 1') gene, which prevents expression of the 'Fragile X Mental Retardation Protein' (FMRP). In FXS, the absence of FMRP leads to altered structural and functional development of the synapse, while preventing activity-based synapse maturation and synaptic pruning, which are essential for normal brain development and cognitive development. Possible impairments in information processing can be non-invasively investigated using electrophysiology.

METHODS

We compared auditory (AEP) and visual (VEP) evoked potentials in twelve adolescents and young adults (10-22 years) affected by FXS to healthy controls matched by chronological age (N=12) and developmental age of cognitive functioning (N=9; 5-7 years), using analysis of variance.

RESULTS

In the visual modality, the N70 and N2 amplitude have been found increased in FXS in comparison to the chronological, but not the developmental control group at occipital sites, whereas in the auditory modality N1, P2 and N2 amplitude as well as N2 latency have been found increased in FXS, relative to both chronological and developmental control groups at mid-central sites.

CONCLUSIONS

The AEP/VEP profile suggests disruptions in sensory processing specific to FXS that exceed immaturity of physiological activity. In addition, the auditory modality seems to be more affected than the visual modality. Results are discussed in light of possible underlying neuronal mechanisms, including deficits in synaptic pruning and neuronal inhibition that might account for a hyperreactive nervous system in FXS.

Topological methods reveal high and low functioning neuro-phenotypes within fragile X syndrome

Fragile X syndrome (FXS), due to mutations of the FMR1 gene, is the most common known inherited cause of developmental disability as well as the most common single-gene risk factor for autism. Our goal was to examine variation in brain structure in FXS with topological data analysis (TDA), and to assess how such variation is associated with measures of IQ and autism-related behaviors. To this end, we analyzed imaging and behavioral data from young boys (n = 52; aged 1.57-4.15 years) diagnosed with FXS. Application of topological methods to structural MRI data revealed two large subgroups within the study population. Comparison of these subgroups showed significant between-subgroup neuroanatomical differences similar to those previously reported to distinguish children with FXS from typically developing controls (e.g., enlarged caudate). In addition to neuroanatomy, the groups showed significant differences in IQ and autism severity scores. These results suggest that despite arising from a single gene mutation, FXS may encompass two biologically, and clinically separable phenotypes. In addition, these findings underscore the potential of TDA as a powerful tool in the search for biological phenotypes of neuropsychiatric disorders.

Testing for association of the monoamine oxidase A promoter polymorphism with brain structure volumes in both autism and the fragile X syndrome

BACKGROUND

Autism and the fragile X syndrome (FXS) are related to each other genetically and symptomatically. A cardinal biological feature of both disorders is abnormalities of cerebral cortical brain volumes. We have previously shown that the monoamine oxidase A (MAOA) promoter polymorphism is associated with cerebral cortical volumes in children with autism, and we now sought to determine whether the association was also present in children with FXS.

METHODS

Participants included 47 2-year-old Caucasian boys with FXS, some of whom also had autism, as well as 34 2-year-old boys with idiopathic autism analyzed in a previous study. The MAOA promoter polymorphism was genotyped and tested for relationships with gray and white matter volumes of the cerebral cortical lobes and cerebro-spinal fluid volume of the lateral ventricles.

RESULTS

MAOA genotype effects in FXS children were the same as those previously observed in idiopathic autism: the low activity MAOA promoter polymorphism allele was associated with increased gray and white matter volumes in all cerebral lobes. The effect was most pronounced in frontal lobe gray matter and all three white matter regions: frontal gray, F = 4.39, P = 0.04; frontal white, F = 5.71, P = 0.02; temporal white, F = 4.73, P = 0.04; parieto-occipital white, F = 5.00, P = 0.03. Analysis of combined FXS and idiopathic autism samples produced P values for these regions <0.01 and effect sizes of approximately 0.10.

CONCLUSIONS

The MAOA promoter polymorphism is similarly associated with brain structure volumes in both idiopathic autism and FXS. These data illuminate a number of important aspects of autism and FXS heritability: a genetic effect on a core biological trait of illness, the specificity/generalizability of the genetic effect, and the utility of examining individual genetic effects on the background of a single gene disorder such as FXS.

Chronic metabotropic glutamate receptor 5 inhibition corrects local alterations of brain activity and improves cognitive performance in fragile X mice

BACKGROUND

Fragile X syndrome (FXS) is the most common genetic cause for intellectual disability. Fmr1 knockout (KO) mice are an established model of FXS. Chronic pharmacological inhibition of metabotropic glutamate receptor 5 (mGlu5) in these mice corrects multiple molecular, physiological, and behavioral phenotypes related to patients' symptoms. To better understand the pathophysiology of FXS and the effect of treatment, brain activity was analyzed using functional magnetic resonance imaging in relation to learning and memory performance.

METHODS

Wild-type (WT) and Fmr1 KO animals receiving chronic treatment with the mGlu5 inhibitor CTEP or vehicle were evaluated consecutively for 1) learning and memory performance in the inhibitory avoidance and extinction test, and 2) for the levels of brain activity using continuous arterial spin labeling based functional magnetic resonance imaging. Neural activity patterns were correlated with cognitive performance using a multivariate regression analysis. Furthermore, mGlu5 receptor expression in brains of untreated mice was analyzed by autoradiography and saturation analysis using [(3)H]-ABP688.

RESULTS

Chronic CTEP treatment corrected the learning deficit observed in Fmr1 KO mice in the inhibitory avoidance and extinction test and prevented memory extinction in WT and Fmr1 KO animals. Chronic CTEP treatment normalized perfusion in the amygdala and the lateral hypothalamus in Fmr1 KO mice and furthermore decreased perfusion in the hippocampus and increased perfusion in primary sensorimotor cortical areas. No significant differences in mGlu5 receptor expression levels between Fmr1 WT and KO mice were detected.

CONCLUSIONS

Chronic mGlu5 inhibition corrected the learning deficits and partially normalized the altered brain activity pattern in Fmr1 KO mice.

Outcome measures for clinical trials in fragile X syndrome

OBJECTIVE

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

METHODS

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

RESULTS

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

CONCLUSION

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

Rescue of NMDAR-dependent synaptic plasticity in Fmr1 knock-out mice

Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability and results from a loss of Fragile X mental retardation protein (FMRP). FMRP is important for mRNA shuttling and translational control and binds to proteins important for synaptic plasticity. Like many developmental disorders, FXS is associated with alterations in synaptic plasticity that may impair learning and memory processes in the brain. However, it remains unclear whether FMRP plays a ubiquitous role in synaptic plasticity in all brain regions. We report that a loss of FMRP leads to impairments in N-methyl-D-aspartate receptor (NMDAR)-dependent synaptic plasticity in the dentate gyrus (DG), but not in the cornu ammonis area 1 (CA1) subregion of the hippocampus of adult mice. DG-specific deficits are accompanied by a significant reduction in NMDAR GluN1, GluN2A, and GluN2B subunit levels and reduced serine 831 GluA1 phosphorylation specifically in this region. Importantly, we demonstrate that treatment with NMDAR co-agonists (glycine or D-serine) independently rescue impairments in NMDAR-dependent synaptic plasticity in the DG of the Fragile X mental retardation 1 (Fmr1) knockout mouse. These findings implicate the NMDAR in the pathophysiology of FXS and suggest that indirect agonists of the NMDAR may be a successful therapeutic intervention in FXS.

Repetitive and self-injurious behaviors: associations with caudate volume in autism and fragile X syndrome

Background

Following from previous work suggesting that neurobehavioral features distinguish fragile X and idiopathic variants of autism, we investigated the relationships between four forms of repetitive behavior (stereotypy, self-injury, compulsivity, ritual behavior) and caudate nuclei volume in two groups: boys with fragile X syndrome, a subset of whom met criteria for autism, and a comparison group of boys with idiopathic autism.

Methods

Bilateral caudate nuclei volumes were measured in boys aged 3 to 6 years with fragile X syndrome (n = 41), the subset of boys with fragile X syndrome and autism (n = 16), and boys with idiopathic autism (n = 30). Repetitive behaviors were measured using the Repetitive Behavior Scales-Revised.

Results

For boys with idiopathic autism, left caudate volume was modestly associated with self-injury, while both compulsive and ritual behaviors showed significant positive correlations with bilateral caudate nuclei volumes, replicating previous results. For boys with fragile X syndrome, there was no such association between caudate volume and compulsive behaviors. However, we did identify significant positive correlations between self-injury total scores and number of self-injury topographies with bilateral caudate nuclei volumes.

Conclusions

These findings suggest a specific role for the caudate nucleus in the early pathogenesis of self-injurious behavior associated with both idiopathic autism and fragile X syndrome. Results further indicate that the caudate may be differentially associated with compulsive behavior, highlighting the utility of isolating discrete brain-behavior associations within and between subtypes of autism spectrum disorder.

Neocortical development as an evolutionary platform for intragenomic conflict

Embryonic development in mammals has evolved a platform for genomic conflict between mothers and embryos and, by extension, between maternal and paternal genomes. The evolutionary interests of the mother and embryo may be maximized through the promotion of sex-chromosome genes and imprinted alleles, resulting in the rapid evolution of postzygotic phenotypes preferential to either the maternal or paternal genome. In eutherian mammals, extraordinary in utero maternal investment in the brain, and neocortex especially, suggests that convergent evolution of an expanded mammalian neocortex along divergent lineages may be explained, in part, by parent-of-origin-linked gene expression arising from parent-offspring conflict. The influence of this conflict on neocortical development and evolution, however, has not been investigated at the genomic level. In this hypothesis and theory article, we provide preliminary evidence for positive selection in humans in the regions of two platforms of intragenomic conflict—chromosomes 15q11-q13 and X—and explore the potential relevance of cis-regulated imprinted domains to neocortical expansion in mammalian evolution. We present the hypothesis that maternal- and paternal-specific pressures on the developing neocortex compete intragenomically to influence neocortical expansion in mammalian evolution.

Sex chromosomes and the brain: a study of neuroanatomy in XYY syndrome

AIM

To assess global and regional brain matter variations associated with XYY syndrome by comparison with Klinefelter syndrome and typical development.

METHODS

We used two conceptually distinct voxel-based magnetic resonance imaging methods to examine brain structure in young males with XYY syndrome: (1) volumetric comparison to assess global grey and white matter volumes and (2) support vector machine-based multivariate pattern classification analysis to assess regional neuroanatomy. We assessed verbal, non-verbal, and spatial abilities with the Differential Ability Scales (DAS), and we measured autism diagnostic criteria in eight males with XYY syndrome using the Social Responsiveness Scale and the Autism Diagnostic Interview-Revised (ADI-R).

RESULTS

A comparison of 36 typically developing males (mean age 11 y, SD 1 y 9 mo), 31 males with Klinefelter syndrome (mean age 9 y 8 mo, SD 1 y 8 mo), and eight males with XYY syndrome (mean age 11 y 6 mo, SD 1 y 11 mo) showed that total white and grey matter volumes were significantly, or nearly significantly, higher in males with XYY syndrome than in males belonging to the other two groups (grey matter: XYY males vs typically developing males, p<0.006; XYY vs males with Klinefelter syndrome, p<0.001; white matter: XYY males vs typically developing males, p=0.061; XYY males vs males with Klinefelter syndrome, p=0.004). Voxel-based multivariate pattern classification analysis indicates that, after controlling for global volumes, regional brain variations in XYY syndrome are more like those found in Klinefelter syndrome than those occurring in typical development. Further, visualization of classification parameters suggests that insular and frontotemporal grey matter and white matter, including known language areas, are reduced in males with XYY syndrome, similar to what is seen in Klinefelter syndrome. In males with XYY syndrome, DAS verbal and non-verbal scores were significantly lower than in typically developing participants (both p<0.001). DAS scores were not significantly different between XYY and Klinefelter syndrome groups. In five of eight males with XYY syndrome, the Social Responsiveness Scale score exceeded the cut-off for a likely diagnosis of autism spectrum disorder (ASD). In three of eight males with XYY syndrome, the ADI-R score met the cut-off for ASD diagnosis; in another two, ADI-R scores within the social and communication domains met the cut-off values for a diagnosis of ASD.

INTERPRETATION

The results suggest that genetic variations associated with XYY syndrome result in increased brain matter volumes, a finding putatively related to the increased frequency of ASDs in individuals with this condition. In addition, frontotemporal grey and white matter reductions in XYY syndrome provide a likely neuroanatomical correlate for observed language impairments.

Fear-specific amygdala function in children and adolescents on the fragile x spectrum: a dosage response of the FMR1 gene

Mutations of the fragile X mental retardation 1 (FMR1) gene are the genetic cause of fragile X syndrome (FXS). The presence of significant socioemotional problems has been well documented in FXS although the brain basis of those deficits remains unspecified. Here, we investigated amygdala dysfunction and its relation to socioemotional deficits and FMR1 gene expression in children and adolescents on the FX spectrum (i.e., individuals whose trinucleotide CGG repeat expansion from 55 to over 200 places them somewhere within the fragile X diagnostic range from premutation to full mutation). Participants performed an fMRI task in which they viewed fearful, happy, and scrambled faces. Neuroimaging results demonstrated that FX participants revealed significantly attenuated amygdala activation in Fearful > Scrambled and Fearful > Happy contrasts compared with their neurotypical counterparts, while showing no differences in amygdala volume. Furthermore, we found significant relationships between FMR1 gene expression, anxiety/social dysfunction scores, and reduced amygdala activation in the FX group. In conclusion, we report novel evidence regarding a dosage response of the FMR1 gene on fear-specific functions of the amygdala, which is associated with socioemotional deficits in FXS.

Multivariate pattern analysis reveals subtle brain anomalies relevant to the cognitive phenotype in neurofibromatosis type 1

Neurofibromatosis Type 1 (NF1) is a common genetic condition associated with cognitive dysfunction. However, the pathophysiology of the NF1 cognitive deficits is not well understood. Abnormal brain structure, including increased total brain volume, white matter (WM) and grey matter (GM) abnormalities have been reported in the NF1 brain. These previous studies employed univariate model-driven methods preventing detection of subtle and spatially distributed differences in brain anatomy. Multivariate pattern analysis allows the combination of information from multiple spatial locations yielding a discriminative power beyond that of single voxels. Here we investigated for the first time subtle anomalies in the NF1 brain, using a multivariate data-driven classification approach. We used support vector machines (SVM) to classify whole-brain GM and WM segments of structural T1 -weighted MRI scans from 39 participants with NF1 and 60 non-affected individuals, divided in children/adolescents and adults groups. We also employed voxel-based morphometry (VBM) as a univariate gold standard to study brain structural differences. SVM classifiers correctly classified 94% of cases (sensitivity 92%; specificity 96%) revealing the existence of brain structural anomalies that discriminate NF1 individuals from controls. Accordingly, VBM analysis revealed structural differences in agreement with the SVM weight maps representing the most relevant brain regions for group discrimination. These included the hippocampus, basal ganglia, thalamus, and visual cortex. This multivariate data-driven analysis thus identified subtle anomalies in brain structure in the absence of visible pathology. Our results provide further insight into the neuroanatomical correlates of known features of the cognitive phenotype of NF1.

Trajectories of early brain volume development in fragile X syndrome and autism

OBJECTIVE

To examine patterns of early brain growth in young children with fragile X syndrome (FXS) compared with a comparison group (controls) and a group with idiopathic autism.

METHOD

The study included 53 boys 18 to 42 months of age with FXS, 68 boys with idiopathic autism (autism spectrum disorder), and a comparison group of 50 typically developing and developmentally delayed controls. Structural brain volumes were examined using magnetic resonance imaging across two time points, at 2 to 3 and again at 4 to 5 years of age, and total brain volumes and regional (lobar) tissue volumes were examined. In addition, a selected group of subcortical structures implicated in the behavioral features of FXS (e.g., basal ganglia, hippocampus, amygdala) was studied.

RESULTS

Children with FXS had larger global brain volumes compared with controls but were not different than children with idiopathic autism, and the rate of brain growth from 2 to 5 years of age paralleled that seen in controls. In contrast to children with idiopathic autism who had generalized cortical lobe enlargement, children with FXS showed specific enlargement in the temporal lobe white matter, cerebellar gray matter, and caudate nucleus, but a significantly smaller amygdala.

CONCLUSIONS

This structural longitudinal magnetic resonance imaging study of preschoolers with FXS observed generalized brain overgrowth in children with FXS compared with controls, evident at age 2 and maintained across ages 4 to 5. In addition, different patterns of brain growth that distinguished boys with FXS from boys with idiopathic autism were found.

Conceptualizing neurodevelopmental disorders through a mechanistic understanding of fragile X syndrome and Williams syndrome

PURPOSE OF REVIEW

The overarching goal of this review is to compare and contrast the cognitive-behavioral features of fragile X syndrome (FraX) and Williams syndrome and to review the putative neural and molecular underpinnings of these features. Information is presented in a framework that provides guiding principles for conceptualizing gene-brain-behavior associations in neurodevelopmental disorders.

RECENT FINDINGS

Abnormalities, in particular cognitive-behavioral domains with similarities in underlying neurodevelopmental correlates, occur in both FraX and Williams syndrome including aberrant frontostriatal pathways leading to executive function deficits, and magnocellular/dorsal visual stream, superior parietal lobe, inferior parietal lobe, and postcentral gyrus abnormalities contributing to deficits in visuospatial function. Compelling cognitive-behavioral and neurodevelopmental contrasts also exist in these two disorders, for example, aberrant amygdala and fusiform cortex structure and function occurring in the context of contrasting social behavioral phenotypes, and temporal cortical and cerebellar abnormalities potentially underlying differences in language function. Abnormal dendritic development is a shared neurodevelopmental morphologic feature between FraX and Williams syndrome. Commonalities in molecular machinery and processes across FraX and Williams syndrome occur as well - microRNAs involved in translational regulation of major synaptic proteins; scaffolding proteins in excitatory synapses; and proteins involved in axonal development.

SUMMARY

Although the genetic variations leading to FraX and Williams syndrome are different, important similarities and contrasts in the phenotype, neurocircuitry, molecular machinery, and cellular processes in these two disorders allow for a unique approach to conceptualizing gene-brain-behavior links occurring in neurodevelopmental disorders.

The challenges and promise of neuroimaging in psychiatry

Neuroimaging is central to the quest for a biological foundation of psychiatric diagnosis but so far has not yielded clinically relevant biomarkers for mental disorders. This review addresses potential reasons for this limitation and discusses refinements of paradigms and analytic techniques that may yield improved diagnostic and prognostic accuracy. Neuroimaging can also be used to probe genetically defined biological pathways underlying mental disorders, for example through the genetic imaging of variants discovered in genome-wide association studies. These approaches may ultimately reveal mechanisms through which genes contribute to psychiatric symptoms and how pharmacological and psychological interventions exert their effects.

Heart activity and autistic behavior in infants and toddlers with fragile X syndrome

The present study contrasted physiological arousal in infants and toddlers with fragile X syndrome to typically developing control participants and examined physiological predictors early in development to autism severity later in development in fragile X syndrome. Thirty-one males with fragile X syndrome (ages 8-40 months) and 25 age-matched control participants were included. The group with fragile X syndrome showed shorter interbeat intervals (IBIs), lower vagal tone (VT), and less modulation of IBI. Data suggested a nonlinear effect with IBI and autistic behavior; however, a linear effect with VT and autistic behavior emerged. These findings suggest that atypical physiological arousal emerges within the first year and predicts severity of autistic behavior in fragile X syndrome. These relationships are complex and dynamic, likely reflecting endogenous factors assumed to reflect atypical brain function secondary to reduced fragile X mental retardation protein. This research has important implications for the early identification and treatment of autistic behaviors in young children with fragile X syndrome.

Comprehensive neurocognitive endophenotyping strategies for mouse models of genetic disorders

There is a need for refinement of the current behavioral phenotyping methods for mouse models of genetic disorders. The current approach is to perform a behavioral screen using standardized tasks to define a broad phenotype of the model. This phenotype is then compared to what is known concerning the disorder being modeled. The weakness inherent in this approach is twofold: First, the tasks that make up these standard behavioral screens do not model specific behaviors associated with a given genetic mutation but rather phenotypes affected in various genetic disorders; secondly, these behavioral tasks are insufficiently sensitive to identify subtle phenotypes. An alternate phenotyping strategy is to determine the core behavioral phenotypes of the genetic disorder being studied and develop behavioral tasks to evaluate specific hypotheses concerning the behavioral consequences of the genetic mutation. This approach emphasizes direct comparisons between the mouse and human that facilitate the development of neurobehavioral biomarkers or quantitative outcome measures for studies of genetic disorders across species.

Attentional set-shifting in fragile X syndrome

The ability to flexibly adapt to the changing demands of the environment is often reported as a core deficit in fragile X syndrome (FXS). However, the cognitive processes that determine this attentional set-shifting deficit remain elusive. The present study investigated attentional set-shifting ability in fragile X syndrome males with the well-validated intra/extra dimensional set-shifting paradigm (IED) which offers detailed assessment of rule learning, reversal learning, and attentional set-shifting ability within and between stimulus dimensions. A novel scoring method for IED stage errors was employed to interpret set-shifting failure in terms of repetitive decision-making, distraction to irrelevance, and set-maintenance failure. Performance of FXS males was compared to typically developing children matched on mental age, adults matched on chronological age, and individuals with Down syndrome matched on both mental and chronological age. Results revealed that a significant proportion of FXS males already failed prior to the intra-dimensional set-shift stage, whereas all control participants successfully completed the stages up to the crucial extra-dimensional set-shift. FXS males showed a specific weakness in reversal learning, which was characterized by repetitive decision-making during the reversal of newly acquired stimulus-response associations in the face of simple stimulus configurations. In contrast, when stimulus configurations became more complex, FXS males displayed increased distraction to irrelevant stimuli. These findings are interpreted in terms of the cognitive demands imposed by the stages of the IED in relation to the alleged neural deficits in FXS.

Molecular and genetic analysis of the Drosophila model of fragile X syndrome

The Drosophila genome contains most genes known to be involved in heritable disease. The extraordinary genetic malleability of Drosophila, coupled to sophisticated imaging, electrophysiology, and behavioral paradigms, has paved the way for insightful mechanistic studies on the causes of developmental and neurological disease as well as many possible interventions. Here, we focus on one of the most advanced examples of Drosophila genetic disease modeling, the Drosophila model of Fragile X Syndrome, which for the past decade has provided key advances into the molecular, cellular, and behavioral defects underlying this devastating disorder. We discuss the multitude of RNAs and proteins that interact with the disease-causing FMR1 gene product, whose function is conserved from Drosophila to human. In turn, we consider FMR1 mechanistic relationships in non-neuronal tissues (germ cells and embryos), peripheral motor and sensory circuits, and central brain circuits involved in circadian clock activity and learning/memory.

Reduced cortical thickness in mental retardation

Mental retardation is a developmental disorder associated with impaired cognitive functioning and deficits in adaptive behaviors. Many studies have addressed white matter abnormalities in patients with mental retardation, while the changes of the cerebral cortex have been studied to a lesser extent. Quantitative analysis of cortical integrity using cortical thickness measurement may provide new insights into the gray matter pathology. In this study, cortical thickness was compared between 13 patients with mental retardation and 26 demographically matched healthy controls. We found that patients with mental retardation had significantly reduced cortical thickness in multiple brain regions compared with healthy controls. These regions include the bilateral lingual gyrus, the bilateral fusiform gyrus, the bilateral parahippocampal gyrus, the bilateral temporal pole, the left inferior temporal gyrus, the right lateral orbitofrontal cortex and the right precentral gyrus. The observed cortical thickness reductions might be the anatomical substrates for the impaired cognitive functioning and deficits in adaptive behaviors in patients with mental retardation. Cortical thickness measurement might provide a sensitive prospective surrogate marker for clinical trials of neuroprotective medications.

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.