Brain imaging in neurogenetic conditions: realizing the potential of behavioral neurogenetics research

Neurobiology of numerical learning

Numerical abilities are complex cognitive skills essential for dealing with requirements of the modern world. Although the brain structures and functions underlying numerical cognition in different species have long been appreciated, genetic and molecular techniques have more recently expanded the knowledge about the mechanisms underlying numerical learning. In this review, we discuss the status of the research related to the neurobiological bases of numerical abilities. We consider how genetic factors have been associated with mathematical capacities and how these link to the current knowledge of brain regions underlying these capacities in human and non-human animals. We further discuss the extent to which significant variations in the levels of specific neurotransmitters may be used as potential markers of individual performance and learning difficulties and take into consideration the therapeutic potential of brain stimulation methods to modulate learning and improve interventional outcomes. The implications of this research for formulating a more comprehensive view of the neural basis of mathematical learning are discussed.

Early impact of X- and Y-chromosome variations (XXX, XXY, XYY) on social communication and social emotional development in 1-2-year-old children

Sex chromosome trisomies (SCTs) are characterized by an extra X‐ or Y‐chromosome (XXX, XXY, XYY). The present study aims to investigate early signs of social communication and social emotional development in very young children with SCT. Thirty‐four children with SCT (aged 12–24 months) were included in this study, as well as 31 age‐matched controls. Social communication was measured with structured behavior observations according to the Early Social Communication Scales, and social emotional developmental level with the Bayley Social Emotional parental questionnaire. Recruitment and assessment took place in the Netherlands and in the United States. On average, 12–24‐month old children with SCT showed difficulties with early social communication, more so in responding to others as compared to initiating social communications. During social interactions, children with SCT made less frequent eye contact, compared to controls. Also, difficulties in acquiring social emotional milestones were found in 1‐year old children with SCT, with 44% of the children having social emotional vulnerabilities in the borderline or extremely low range, compared to typically developing children. In this cohort, no significant predictive effects of karyotype‐subtype (XXX, XXY, XYY) were found. Already from a very early age, SCT can be associated with increased risk for vulnerabilities in adaptive social functioning. These findings suggest that SCT impact the maturation of the social brain already from an early age, and stress the importance of early monitoring and (preventive) support early social development in young children with SCT.

Task-Related Brain Connectivity Activation Functional Magnetic Resonance Imaging in Intellectual Disability Population: A Meta-analytic Study

Introduction: Neuroimaging studies of intellectual disability (ID) have been published over the last three decades, but the findings are often inconsistent, and therefore, the neural correlates of ID remain elusive. This article aims to study the different publications in task-functional magnetic resonance imaging (fMRI) and different ID populations to make a qualitative and quantitative analysis on this field. Methods: After duplicates were removed, only 10 studies matching our inclusion criteria were incorporated. Moreover, a quality assessment of the included studies was done. Qualitative results of the different articles were analyzed, separated by type of task and type of ID. Seed-based d mapping (SDM) software was used. Results: The right temporal gyrus was more activated in control subjects than in ID. Concretely, the right temporal gyrus is implicated in many cognitive domains as semantic memory processing and language. Moreover, it can be highly influenced by the type of task used in every study. Heterogeneity was not detected. A jackknife sensitivity analysis was also estimated to improve the analysis reliability, and both results were confirmed. Conclusions: More task-fMRI studies on ID must be published to add larger samples to address the pathophysiological questions more directly.

Structural and functional brain alterations revealed by neuroimaging in CNV carriers

Copy Number Variants (CNVs) are associated with elevated rates of neuropsychiatric disorders. A 'genetics-first' approach, involving the CNV effects on the brain, irrespective of clinical symptomatology, allows investigation of mechanisms underlying neuropsychiatric disorders in the general population. Recent years have seen an increasing number of larger multisite neuroimaging studies investigating the effect of CNVs on structural and functional brain endophenotypes. Alterations overlap with those found in idiopathic psychiatric conditions but effect sizes are twofold to fivefold larger. Here we review new CNV-associated structural and functional brain alterations and outline the future of neuroimaging genomics research, with particular emphasis on developing new resources for the study of high-risk CNVs and rare genomic variants.

A review of neurocognitive functioning and risk for psychopathology in sex chromosome trisomy (47,XXY, 47,XXX, 47, XYY)

PURPOSE OF REVIEW

About one in 650-1000 children is born with an extra X or Y chromosome, referred to as sex chromosome trisomies (SCTs). Studying SCTs may uncover unique insights in neurodevelopmental pathways underlying the risk for neurobehavioral problems and psychopathology. There is also a clinical need for more knowledge about the phenotype of SCT with the recent introduction of noninvasive prenatal screening.

RECENT FINDINGS

The reviewed studies illustrate an increased vulnerability for psychopathology such as (symptoms of) autism spectrum disorder, attention-deficit/hyperactivity disorder, anxiety, depression and, to a lesser degree, psychotic disorders. Although traditionally the primary focus has been on language and learning problems, recent research suggests that impairments in executive functioning, social cognition and emotion regulation may also be key factors underlying the risk for neurobehavioral problems.

SUMMARY

The research field of SCT is in need of a more longitudinal perspective to identify early markers of 'at risk' development, and to assess the effectiveness of early interventions. Neurocognitive markers that signal compromised neurodevelopment may prove to be helpful in this. Variability in the SCT phenotype provides a unique opportunity to identify not only genetic but also environmental factors that shape neurodevelopmental outcome, calling for studies focused on understanding individual differences.

A Different Brain: Anomalies of Functional and Structural Connections in Williams Syndrome

We describe the results of a functional and structural brain connectivity analysis comparing a homogeneous group of 10 young adults with Williams Syndrome (WS; 3 females, age 20. 7 ± 3.7 years, age range 17.4–28.7 years) to a group of 18 controls of similar age (3 females, age 23.9 ± 4.4 years, age range 16.8–30.2), with the aim to increase knowledge of the structure – function relationship in WS. Subjects underwent a 3T brain MRI exam including anatomical, functional (resting state) and structural (diffusion MRI) sequences. We found convergent anomalies in structural and functional connectivity in the WS group. Altered Fractional Anisotropy (FA) values in parieto-occipital regions were associated with increased connectivity in the antero-posterior pathways linking parieto-occipital with frontal regions. The analysis of resting state data showed altered functional connectivity in the WS group in main brain networks (default mode, executive control and dorsal attention, sensori-motor, fronto—parietal, ventral stream). The combined analysis of functional and structural connectivity displayed a different pattern in the two groups: in controls the highest agreement was found in frontal and visual areas, whereas in WS patients in posterior regions (parieto-occipital and temporal areas). These preliminary findings may reflect an altered “wiring” of the brain in WS, which can be driven by hyper-connectivity of the posterior regions as opposed to disrupted connectivity in the anterior areas, supporting the hypothesis that a different brain (organization) could be associated with a different (organization of) behavior in Williams Syndrome.

White matter microstructure in a genetically defined group at increased risk of autism symptoms, and a comparison with idiopathic autism: an exploratory study

Klinefelter syndrome (47,XXY) is associated with physical, behavioral, and cognitive consequences. Deviations in brain structure and function have been reported, but structural characteristics of white matter have barely been assessed. This exploratory diffusion tensor imaging study assessed white matter microstructure in boys with 47,XXY compared with non-clinical, male controls. Additionally, both similarities and differences between 47,XXY and autism spectrum disorders (ASD) have been reported in cognition, behavior and neural architecture. To further investigate these brain-behavior pathways, white matter microstructure in boys with 47,XXY was compared to that of boys with ASD. Fractional anisotropy (FA), radial diffusivity (Dr), axial diffusivity (Da), and mean diffusivity (MD) were assessed in 47,XXY (n = 9), ASD (n = 18), and controls (n = 14), using tract-based spatial statistics. Compared with controls, boys with 47,XXY have reduced FA, coupled with reduced Da, in the corpus callosum. Boys with 47,XXY also have reduced Dr. in the left anterior corona radiata and sagittal striatum compared with controls. Compared with boys with ASD, boys with 47,XXY show reduced Da in the right inferior fronto-occipital fasciculus. Although this study is preliminary considering the small sample size, reduced white matter integrity in the corpus callosum may be a contributing factor in the cognitive and behavioral problems associated with 47,XXY. In addition, the differences in white matter microstructure between 47,XXY and ASD may be important for our understanding of the mechanisms that are fundamental to behavioral outcome in social dysfunction, and may be targeted through intervention.

Genetic Consideration of Schizotypal Traits: A Review

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

Fragile X syndrome: A review of clinical management

The fragile X mental retardation 1 gene, which codes for the fragile X mental retardation 1 protein, usually has 5 to 40 CGG repeats in the 5' untranslated promoter. The full mutation is the almost always the cause of fragile X syndrome (FXS). The prevalence of FXS is about 1 in 4,000 to 1 in 7,000 in the general population although the prevalence varies in different regions of the world. FXS is the most common inherited cause of intellectual disability and autism. The understanding of the neurobiology of FXS has led to many targeted treatments, but none have cured this disorder. The treatment of the medical problems and associated behaviors remain the most useful intervention for children with FXS. In this review, we focus on the non-pharmacological and pharmacological management of medical and behavioral problems associated with FXS as well as current recommendations for follow-up and surveillance.

Reduced fronto-temporal and limbic connectivity in the 22q11.2 deletion syndrome: vulnerability markers for developing schizophrenia?

The 22q11.2 deletion syndrome (22q11DS) is a widely recognized genetic model allowing the study of neuroanatomical biomarkers that underlie the risk for developing schizophrenia. Recent advances in magnetic resonance image analyses enable the examination of structural connectivity integrity, scarcely used in the 22q11DS field. This framework potentially provides evidence for the disconnectivity hypothesis of schizophrenia in this high-risk population. In the present study, we quantify the whole brain white matter connections in 22q11DS using deterministic tractography. Diffusion Tensor Imaging was acquired in 30 affected patients and 30 age- and gender-matched healthy participants. The Human Connectome technique was applied to register white matter streamlines with cortical anatomy. The number of fibers (streamlines) was used as a measure of connectivity for comparison between groups at the global, lobar and regional level. All statistics were corrected for age and gender. Results showed a 10% reduction of the total number of fibers in patients compared to controls. After correcting for this global reduction, preserved connectivity was found within the right frontal and right parietal lobes. The relative increase in the number of fibers was located mainly in the right hemisphere. Conversely, an excessive reduction of connectivity was observed within and between limbic structures. Finally, a disproportionate reduction was shown at the level of fibers connecting the left fronto-temporal regions. We could therefore speculate that the observed disruption to fronto-temporal connectivity in individuals at risk of schizophrenia implies that fronto-temporal disconnectivity, frequently implicated in the pathogenesis of schizophrenia, could precede the onset of symptoms and, as such, constitutes a biomarker of the vulnerability to develop psychosis. On the contrary, connectivity alterations in the limbic lobe play a role in a wide range of psychiatric disorders and therefore seem to be less specific in defining schizophrenia.

Neuroanatomical phenotype of Klinefelter syndrome in childhood: a voxel-based morphometry study

Klinefelter syndrome (KS) is a genetic disorder characterized by a supernumerary X chromosome. As such, KS offers a naturally occurring human model for the study of both X-chromosome gene expression and androgen on brain development. Previous neuroimaging studies have revealed neuroanatomical variations associated with KS, but have differed widely with respect to subject inclusion criteria, including mosaicism, pubertal status, and history of testosterone replacement therapy (TRT), all factors likely to influence neurodevelopment. We conducted a voxel-based morphometry study of regional gray and white matter (GM and WM, respectively) volumes in 31 KS males (mean age, 9.69 ± 1.70 years) and 36 typically developing (TD) male controls (10.99 ± 1.72 years). None of the participants with KS had received TRT, and all were prepubertal and had nonmosaic 47,XXY karyotypes. After controlling for age, males with KS showed trends (0.05 < p < 0.10) for significantly reduced total gray matter volume (TGMV) and total white matter volume (TWMV), relative to TD males. After controlling for TGMV and age, the KS group had significantly increased sensorimotor and parietal-occipital GM and significantly reduced amygdalar, hippocampal, insular, temporal, and inferior frontal GM relative to TD controls. After controlling for TWMV and age, the KS group had significantly increased left parietal WM as well as significantly reduced frontal and temporal WM. These findings are indicative of a characteristic prepubertal neuroanatomical phenotype that may be associated with cognitive-behavioral features of KS. This work offers new insight into the relationships among X-chromosome gene expression, neuroanatomy, and cognitive-behavioral functions impaired in KS, including language and attention.

Vulnerability for psychopathology in Klinefelter syndrome: age-specific and cognitive-specific risk profiles

AIM

Studying Klinefelter syndrome (KS) (47,XXY) can reveal insights into mechanisms of neurodevelopment. Our aim was to identify factors that influence risk for psychopathology in this syndrome, with a focus on age-specific and cognitive-specific risk profiles.

METHODS

A total of 73 subjects with KS (25 children and 48 adults) and 93 age-matched controls (53 children and 40 adults) participated in the study. The discrepancy between verbal IQ (VIQ) and performance IQ (PIQ) was assessed using the Wechsler Intelligence Scales. IQ data were only measured in the Klinefelter group. All participants completed the Autism Questionnaire and Schizotypal Personality Questionnaire.

RESULTS

Increased levels of autism traits and schizotypal traits were observed in individuals with KS, with schizotypal traits increasing with age. The VIQ < PIQ group (n = 33) showed significantly increased levels of autism traits compared to the PIQ < VIQ group (n = 12) and controls. The PIQ < VIQ group showed significantly increased levels of schizotypal traits compared to the VIQ < PIQ group and controls. The VIQ-PIQ discrepancy significantly correlated with schizotypal traits and autism traits, in opposite directions.

CONCLUSION

Risk for psychopathology in KS may be age specific as well as dependent on cognitive profile. Relative deficits in verbal abilities seem more strongly associated with increased autism traits, whereas relative deficits in visuospatial abilities seem more strongly associated with increased schizotypal traits.

Structural and functional neuroimaging in Klinefelter (47,XXY) syndrome: a review of the literature and preliminary results from a functional magnetic resonance imaging study of language

Klinefelter (47,XXY) syndrome (KS), the most common form of sex-chromosomal aneuploidy, is characterized by physical, endocrinologic, and reproductive abnormalities. Individuals with KS also exhibit a cognitive/behavioral phenotype characterized by language and language-based learning disabilities and executive and attentional dysfunction in the setting of normal general intelligence. The underlying neurobiologic mechanisms are just now beginning to be elucidated through structural and functional neuroimaging. Here, we review the literature of structural and functional neural findings in KS identified by neuroimaging and present preliminary results from a functional magnetic resonance imaging study examining brain activity during a verb generation task in KS.

Turner syndrome: neuroimaging findings: structural and functional

Neuroimaging studies of Turner syndrome can advance our understanding of the X chromosome in brain development, and the modulatory influence of endocrine factors. There is increasing evidence from neuroimaging studies that TX individuals have significant differences in the anatomy, function, and metabolism of a number of brain regions; including the parietal lobe; cerebellum, amygdala, hippocampus; and basal ganglia; and perhaps differences in "connectivity" between frontal and parieto-occipital regions. Finally, there is preliminary evidence that genomic imprinting, sex hormones and growth hormone have significant modulatory effects on brain maturation in TS.

Insights into brain development from neurogenetic syndromes: evidence from fragile X syndrome, Williams syndrome, Turner syndrome and velocardiofacial syndrome

Over the past few decades, behavioral, neuroimaging and molecular studies of neurogenetic conditions, such as Williams, fragile X, Turner and velocardiofacial (22q11.2 deletion) syndromes, have led to important insights regarding brain development. These investigations allow researchers to examine "experiments of nature" in which the deletion or alteration of one gene or a contiguous set of genes can be linked to aberrant brain structure or function. Converging evidence across multiple imaging modalities has now begun to highlight the abnormal neural circuitry characterizing many individual neurogenetic syndromes. Furthermore, there has been renewed interest in combining analyses across neurogenetic conditions in order to search for common organizing principles in development. In this review, we highlight converging evidence across syndromes from multiple neuroimaging modalities, with a particular emphasis on functional imaging. In addition, we discuss the commonalities and differences pertaining to selective deficits in visuospatial processing that occur across four neurogenetic syndromes. We suggest avenues for future exploration, with the goal of achieving a deeper understanding of the neural abnormalities in these affected populations.

Brain abnormalities in Williams syndrome: a review of structural and functional magnetic resonance imaging findings

Williams syndrome (WS) is rare genetic form of mental retardation caused by a microdeletion on chromosome 7q11.23 that causes cognitive impairment and a variety of physical abnormalities. MRI studies of WS have demonstrated a series of brain abnormalities, including decreased brain size, with a relatively greater decrease in the volume of the cerebral white matter volume as compared to the cerebral gray matter. Moreover there is evidence that the posterior cerebrum is more affected in that persons with WS have a greater ratio of frontal to posterior regional volume. These findings are further supported by automated analyses that have shown reduced gray matter density in the superior parietal lobe areas. Functional MRI studies have demonstrated hypofunction immediately adjacent to, and anterior to, the intraparietal sulcus, a region in which structural brain differences had been identified. These anatomical and functional differences are consistent with the neuropsychological profile of WS - in particular, with evidence of dorsal stream visual processing deficits. To date, however, studies have always been performed in comparison to intellectually average controls. It is not clear, therefore, if findings are specific to the WS population or whether they represent a morphological disturbance characteristic of mental retardation, irrespective of genetic etiology. In this article, we reviewed recent advances underlying the structural and functional neural substrate of WS in Medical Literature Analysis and Retrieval System Online (MEDLINE; 1997-2007).

Behavioural and cognitive phenotypes in idiopathic autism versus autism associated with fragile X syndrome

BACKGROUND

In order to better understand the underlying biological mechanism/s involved in autism, it is important to investigate the cognitive and behavioural phenotypes associated with idiopathic autism (autism without a known cause) and comorbid autism (autism associated with known genetic/biological disorders such as fragile X syndrome). Parental effects associated with each type of autism also serve to cast light on the biological underpinnings of autism.

METHOD

Forty-nine participants with idiopathic autism (AD; Mean age: 11.16; SD: 6.08) and their parents (45 mothers; 34 fathers), and 48 participants with fragile X syndrome and co-morbid autism (FXS/AD; Mean age: 17.30; SD: 10.22) and their parents (32 mothers; 30 fathers) were administered the ADOS-G and the age-appropriate Wechsler test to ascertain autism and cognitive profiles respectively.

RESULTS

The AD and FXS/AD groups showed a similar profile on the ADOS domains, with slightly higher scores on the Communication domain in the FXS/AD group, after adjusting for full-scale IQ. Marked differences between the groups in their cognitive abilities were apparent, with the FXS/AD group showing significantly lower scores on all subtests except Comprehension. While no parental effects were found for the FXS/AD group, a paternal effect was apparent on the combined ADOS score for the AD group. Moreover, midparental effects were found in this group for full-scale IQ (FSIQ) and verbal IQ (VIQ). Analyses also revealed parental effects for the subtests of Similarities, Vocabulary, and Information with predominantly maternal effect, and Digit Span with predominantly paternal effect. Both parents contributed to the midparental effect for Processing Speed.

CONCLUSIONS

The results, together with our previous findings, suggest that the postulated combination of susceptibility genes for autism may primarily involve cognitive rather than behavioural processes.

Defining the social phenotype in Williams syndrome: a model for linking gene, the brain, and behavior

Research into phenotype-genotype correlations in neurodevelopmental disorders has greatly elucidated the contribution of genetic and neurobiological factors to variations in typical and atypical development. Etiologically relatively homogeneous disorders, such as Williams syndrome (WS), provide unique opportunities for elucidating gene-brain-behavior relationships. WS is a neurogenetic disorder caused by a hemizygous deletion of approximately 25 genes on chromosome 7q11.23. This results in a cascade of physical, cognitive-behavioral, affective, and neurobiological aberrations. WS is associated with a markedly uneven neurocognitive profile, and the mature state cognitive profile of WS is relatively well developed. Although anecdotally, individuals with WS have been frequently described as unusually friendly and sociable, personality remains a considerably less well studied area. This paper investigates genetic influences, cognitive-behavioral characteristics, aberrations in brain structure and function, and environmental and biological variables that influence the social outcomes of individuals with WS. We bring together a series of findings across multiple levels of scientific enquiry to examine the social phenotype in WS, reflecting the journey from gene to the brain to behavior. Understanding the complex multilevel scientific perspective in WS has implications for understanding typical social development by identifying important developmental events and markers, as well as helping to define the boundaries of psychopathology.

Neural phenotypes of common and rare genetic variants

Neuroimaging methods offer a powerful way to bridge the gaps between genes, neurobiology and behavior. Such investigations may be further empowered by complementary strategies involving chromosomal abnormalities associated with particular neurobehavioral phenotypes, which can help to localize causative genes and better understand the genetics of complex traits in the general population. Here we review the evidence from studies using these convergent approaches to investigate genetic influences on brain structure: (1) studies of common genetic variations associated with particular neuroanatomic phenotypes, and (2) studies of possible 'genetic subtypes' of neuropsychiatric disorders with very high penetrance, with a focus on neuroimaging studies using novel computational brain mapping algorithms. Finally, we discuss the contribution of behavioral neurogenetics research to our understanding of the genetic basis of neuropsychiatric disorders in the broader population.

Review of twin and family studies on neuroanatomic phenotypes and typical neurodevelopment

This article reviews the extant twin studies employing magnetic resonance imaging data (MRI), with an emphasis on studies of population-based samples. There have been approximately 75 twin reports using MRI, with somewhat under half focusing on typical brain structure. Of these, most are samples of adults. For large brain regions such as lobar volumes, the heritabilities of large brain volumes are consistently high, with genetic factors accounting for at least half of the phenotypic variance. The role of genetics in generating individual differences in the volumes of small brain regions is less clear, mostly due to a dearth of information, but rarely because of disagreement between studies. Multivariate analyses show strong genetic relationships between brain regions. Cortical regions involved in language, executive function, and emotional regulation appear to be more heritable than other areas. Studies of brain shape also show significant, albeit lower, genetic effects on population variance. Finally, there is evidence of significant genetically mediated relationships between intelligence and brain structure. At present, the majority of twin imaging studies are limited by sample sizes small by the standards of behavioral genetics; nevertheless the literature at present represents a pioneering effort in the pursuit of answers to many challenging neurobiological questions.

From genes to brain: understanding brain development in neurogenetic disorders using neuroimaging techniques

For almost two decades, a considerable amount of work has been devoted to the accurate delineation of normal and abnormal brain development using cerebral MRI. In the broad field of neuroimaging research, specific genetic conditions associated with impaired cognitive performances or with psychiatric symptoms have received increased attention because of their potential for revealing insight on the biologic correlates of behavior. First delineated by volumetric measurements of cerebral lobes or regions of interest, new image processing techniques are currently defining cerebral phenotypes associated with neurogenetic disorders with increasing precision. In this article the authors review the contribution of structural brain imaging in advancing our understanding of the pathogenic processes underlying altered brain development in Down, fragile X, and velocardiofacial (22q11DS) syndromes.

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.

Impaired neural networks for approximate calculation in dyscalculic children: a functional MRI study

BACKGROUND

Developmental dyscalculia (DD) is a specific learning disability affecting the acquisition of mathematical skills in children with otherwise normal general intelligence. The goal of the present study was to examine cerebral mechanisms underlying DD.

METHODS

Eighteen children with DD aged 11.2 +/- 1.3 years and twenty age-matched typically achieving schoolchildren were investigated using functional magnetic resonance imaging (fMRI) during trials testing approximate and exact mathematical calculation, as well as magnitude comparison.

RESULTS

Children with DD showed greater inter-individual variability and had weaker activation in almost the entire neuronal network for approximate calculation including the intraparietal sulcus, and the middle and inferior frontal gyrus of both hemispheres. In particular, the left intraparietal sulcus, the left inferior frontal gyrus and the right middle frontal gyrus seem to play crucial roles in correct approximate calculation, since brain activation correlated with accuracy rate in these regions. In contrast, no differences between groups could be found for exact calculation and magnitude comparison. In general, fMRI revealed similar parietal and prefrontal activation patterns in DD children compared to controls for all conditions.

CONCLUSION

In conclusion, there is evidence for a deficient recruitment of neural resources in children with DD when processing analog magnitudes of numbers.

Science and society: applications of behavioural genetics: outpacing the science?

Human behavioural genetics is an established research discipline of the genomic age, and applications for behavioural genetic information are most likely to emerge in areas such as criminal justice, education, employment and insurance. However, behavioural genetic research into personality traits and antisocial behaviour poses several risks; for example, tentative or preliminary research findings might be misused in legal and commercial settings. Scientific caution, public and media education, expert consultation and confidentiality protection are essential for the responsible use of behavioural genetics.

Klinefelter's syndrome (XXY) as a genetic model for psychotic disorders

Males with an extra-X chromosome (Klinefelter's syndrome) frequently, although not always, have an increased prevalence of psychiatric disturbances that range from attention deficit disorder in childhood to schizophrenia or severe affective disorders during adulthood. In addition, they frequently have characteristic verbal deficits. Thus, examining brain magnetic resonance imaging (MRI) scans of these individuals may yield clues to the influence of X chromosome genes on brain structural variation corresponding to psychiatric and cognitive disorders. Eleven adult XXY and 11 age matched XY male controls were examined with a structured psychiatric interview, battery of cognitive tests, and an MRI scan. Ten of eleven of the XXY men had some form of psychiatric disturbance, four of whom had auditory hallucinations compared with none of the XY controls. Significantly smaller frontal lobe, temporal lobe, and superior temporal gyrus (STG) cortical volumes were observed bilaterally in the XXY men. In addition, diffusion tensor imaging (DTI) of white matter integrity resulted in four regions of reduced fractional anisotropy (FA) in XXY men compared with controls, three in the left hemisphere, and one on the right. These correspond to the left posterior limb of the internal capsule, bilateral anterior cingulate, and left arcuate bundle. Specific cognitive deficits in executive functioning attributable to frontal lobe integrity and verbal comprehension were noted. Thus, excess expression of one or more X chromosome genes influences both gray and white matter development in frontal and temporal lobes, as well as white matter tracts leading to them, and may in this way contribute to the executive and language deficits observed in these adults. Future prospective studies are needed to determine which gene or genes are involved and whether their expression could be modified with appropriate treatments early in life. Brain expressed genes that are known to escape inactivation on extra-X chromosomes would be prime candidates.

Renewal of the neurophysiology of language: functional neuroimaging

Functional neuroimaging methods have reached maturity. It is now possible to start to build the foundations of a physiology of language. The remarkable number of neuroimaging studies performed so far illustrates the potential of this approach, which complements the classical knowledge accumulated on aphasia. Here we attempt to characterize the impact of the functional neuroimaging revolution on our understanding of language. Although today considered as neuroimaging techniques, we refer less to electroencephalography and magnetoencephalography studies than to positron emission tomography and functional magnetic resonance imaging studies, which deal more directly with the question of localization and functional neuroanatomy. This review is structured in three parts. 1) Because of their rapid evolution, we address technical and methodological issues to provide an overview of current procedures and sketch out future perspectives. 2) We review a set of significant results acquired in normal adults (the core of functional imaging studies) to provide an overview of language mechanisms in the "standard" brain. Single-word processing is considered in relation to input modalities (visual and auditory input), output modalities (speech and written output), and the involvement of "central" semantic processes before sentence processing and nonstandard language (illiteracy, multilingualism, and sensory deficits) are addressed. 3) We address the influence of plasticity on physiological functions in relation to its main contexts of appearance, i.e., development and brain lesions, to show how functional imaging can allow fine-grained approaches to adaptation, the fundamental property of the brain. In closing, we consider future developments for language research using functional imaging.

Imaging of neurogenetic and neurometabolic disorders of childhood

Magnetic resonance imaging (MRI) has emerged as a powerful tool in the study of normal and abnormal brain structure, function, and biochemistry. In particular, functional MRI has come into its own as a tool to study normal and abnormal brain functions such as learning, memory, and motor learning, as well as delineation of neurogenetic cognitive phenotypes. White matter microstructure can be studied using diffusion tensor imaging, which may allow abnormal white matter to be visualized prior to abnormalities on anatomic MRI. Magnetic resonance spectroscopy, a noninvasive method to study brain biochemistry, may allow for the delineation of regional metabolic changes as a result of disease progression and/or therapeutic intervention. With MRI techniques, one can investigate the relationship between structure, function, genes, and behavior. This report discusses the research applications of MRI to the study of neurogenetic disorders of childhood.

Functional and structural alterations of the intraparietal sulcus in a developmental dyscalculia of genetic origin

Cognitive theories of numerical representation suggest that understanding of numerical quantities is driven by a magnitude representation associated with the intraparietal sulcus and possibly under genetic control. The aim of this study was to investigate, using fMRI and structural imaging, the interaction between the abnormal development of numerical representation in an X-linked condition, Turner syndrome (TS), and the development of the intraparietal sulcus. fMRI during exact and approximate calculation in TS showed an abnormal modulation of intraparietal activations as a function of number size. Morphological analysis revealed an abnormal length, depth, and sulcal geometry of the right intraparietal sulcus, suggesting an important disorganization of this region in TS. Thus, a genetic form of developmental dyscalculia can be related to both functional and structural anomalies of the right intraparietal sulcus, suggesting a crucial role of this region in the development of arithmetic abilities.

Phenotypic variation and FMRP levels in fragile X

Data on the relationships between cognitive and physical phenotypes, and a deficit of fragile X mental retardation 1 (FMR1) gene-specific protein product, FMRP, are presented and discussed in context with earlier findings. The previously unpublished results obtained, using standard procedures of regression and correlations, showed highly significant associations in males between FMRP levels and the Wechsler summary and subtest scores and in females between these levels and the full-scale intelligence quotient (FSIQ), verbal and performance IQ, and some Wechsler subtest scores. The published results based on data from 144 extended families with fragile X, recruited from Australia and the United States within a collaborative NIH-supported project, were obtained using robust modification of maximum likelihood in pedigrees. The results indicated that processing speed, short-term memory, and the ability to control attention, especially in the context of regulating goal-directed behavior, may be primarily affected by the FMRP depletion. The effect of this depletion on physical phenotype was also demonstrated, especially on body and head height and extensibility of finger joints. It is recommended that further studies should rely on more accurate measures of FMRP levels, and use of larger samples, to overcome extensive variability in the data.

Effect of the Fragile X Status Categories and the Fragile X Mental Retardation Protein Levels on Executive Functioning in Males and Females With Fragile X

The effects of a fragile X disorder on executive function impairment were assessed in 144 extended families, which included individuals with fragile X premutation and full mutation and their relatives without fragile X. A modification of the maximum-likelihood estimators for pedigree data, as well as ordinal logistic regression, were used in data analysis. The most outstanding deficit, occurring especially in males, involved impaired capacity to use an intention to regulate purposeful behavior. This deficit occurred independently of general cognitive impairment but was related to depletion of fragile X mental retardation 1 gene protein product. The other executive function deficits were accounted for by the general cognitive impairment. Possible mechanisms of the effect of fragile X premutation on impairments of executive functioning are considered.

The schizophrenia phenotype in 22q11 deletion syndrome

OBJECTIVE

This study investigated the schizophrenia phenotype in 24 subjects with 22q11 deletion syndrome (22qDS) and schizophrenia (22qDS-schizophrenia), a rare but relatively homogenous genetic subtype of schizophrenia associated with a microdeletion on chromosome 22. Individuals with 22qDS are at genetically high risk for schizophrenia.

METHOD

Standard measures of signs, symptoms, and course of schizophrenia were assessed in 16 adults with 22qDS-schizophrenia who did not meet criteria for mental retardation and in 46 adults with schizophrenia without evidence of 22qDS from a community familial sample.

RESULTS

There were no significant differences in age at onset, lifetime or cross-sectional core positive and negative schizophrenic symptoms, or global functioning between the two groups of patients with schizophrenia. Patients with 22qDS-schizophrenia had higher excitement subscale scores and less lifetime substance use than the comparison patients with schizophrenia, but no significant differences in anxiety-depression symptom severity were found between the groups.

CONCLUSIONS

These findings indicate that the core clinical schizophrenia phenotype would not distinguish individuals with a 22qDS subtype from those with schizophrenia who did not have the 22qDS subtype. The results provide further support for the utility of 22qDS-schizophrenia as a neurodevelopmental model of schizophrenia as well as support for prospective studies of individuals with 22qDS to help identify precursors of schizophrenia.

Abnormal prefrontal cortex function during response inhibition in Turner syndrome: functional magnetic resonance imaging evidence

BACKGROUND

Turner syndrome (TuS) arises from the partial or complete absence of one X chromosome. Although neuropsychological studies report impaired attentional function and response inhibition in TuS, the neural correlates of these cognitive problems are unknown.

METHODS

Eleven female subjects with TuS and 11 individually matched normal control subjects were imaged using functional magnetic resonance imaging while performing a Go/NoGo task.

RESULTS

Groups did not differ on accuracy or reaction time; however, the TuS group activated more in the bilateral superior and middle frontal gyri than control subjects. Control subjects did not activate more than the TuS group in any region.

CONCLUSION

These findings suggest that female subjects with TuS compensate for executive dysfunction via recruitment of additional prefrontal cortex regions involved in inhibition, attention, and working memory, functions necessary for successful performance of Go/NoGo tasks. Elucidating brain function in TuS will advance our understanding of the influence of X-chromosome genes on neurodevelopment and brain function and contribute to planning future intervention strategies.

Ethics of neuroimaging in pediatric development

Neuroimaging in pediatrics is accompanied by all the ethical dilemmas associated with neuroimaging in adults, magnified significantly. The defining characteristics of childhood make working ethically with the population particularly problematic. Children have not developed the rational capabilities necessary to make informed decisions and the variability and change associated with development contribute to heightened risks and/or benefits of any procedure and limit interpretation of data. As a consequence, fewer pediatric than adult neuroimaging research studies have been done, further limiting general knowledge of the field. Significant strides have been made just within the past few years with the collection of normative data sets of healthy children. Recommendations on how to proceed with pediatric neuroimaging studies while ensuring ethical treatment of the participants are presented.

Effect of the deficits of fragile X mental retardation protein on cognitive status of fragile x males and females assessed by robust pedigree analysis

The effect of the fragile X mental retardation 1 (FMR1) gene product (fragile X mental retardation protein [FMRP]) deficits on Full-Scale IQ (FSIQ) and FSIQ-adjusted Wechsler subtests and index scores in fragile X disorder were assessed using a robust modification of the maximum likelihood estimators for pedigree data. The results from 144 extended families have demonstrated a linear effect of progressively reduced levels of FMRP on the FSIQ and all subtest and summary scores in either gender. The effect of FMRP in decreasing FSIQ-adjusted subtest scores was highly significant for Digit Span, Symbol Search, Object Assembly, and Picture Arrangement, with a consistent trend in both genders. Heritability for FSIQ and unadjusted subtest scores estimated from the covariance model did not exceed 50% and varied widely from the highest for Verbal score to the lowest for Picture Completion score. Possible mechanisms by which FMRP deficit impacts on specific weaknesses in fragile X are considered on the basis of present data.

A converging-methods approach to fragile X syndrome

Converging approaches across domains of brain anatomy, cell biology, and behavior indicate that Fragile X syndrome, arising from impaired expression of a single gene and protein, appears to involve an aberration of normal developmental processes. Synapse overproduction and selective elimination, or pruning, characterize normal brain development. In autopsy tissue from Fragile X patients and in a knockout mouse model of the disease, synapse overproduction appears to occur unaccompanied by synapse pruning and maturation, leaving an excess of immature spine synapses in place. The absence of the Fragile X protein seems to impair the synthesis of important proteins at synapses. The developmental outcome in Fragile X is a nervous system that is relatively disorganized, resulting in disrupted perceptual, and cognitive social, behavior.

Patterns of dysmorphic features in schizophrenia

Congenital dysmorphic features are prevalent in schizophrenia and may reflect underlying neurodevelopmental abnormalities. A cluster analysis approach delineating patterns of dysmorphic features has been used in genetics to classify individuals into more etiologically homogeneous subgroups. In the present study, this approach was applied to schizophrenia, using a sample with a suspected genetic syndrome as a testable model. Subjects (n = 159) with schizophrenia or schizoaffective disorder were ascertained from chronic patient populations (random, n = 123) or referred with possible 22q11 deletion syndrome (referred, n = 36). All subjects were evaluated for presence or absence of 70 reliably assessed dysmorphic features, which were used in a three-step cluster analysis. The analysis produced four major clusters with different patterns of dysmorphic features. Significant between-cluster differences were found for rates of 37 dysmorphic features (P < 0.05), median number of dysmorphic features (P = 0.0001), and validating features not used in the cluster analysis: mild mental retardation (P = 0.001) and congenital heart defects (P = 0.002). Two clusters (1 and 4) appeared to represent more developmental subgroups of schizophrenia with elevated rates of dysmorphic features and validating features. Cluster 1 (n = 27) comprised mostly referred subjects. Cluster 4 (n = 18) had a different pattern of dysmorphic features; one subject had a mosaic Turner syndrome variant. Two other clusters had lower rates and patterns of features consistent with those found in previous studies of schizophrenia. Delineating patterns of dysmorphic features may help identify subgroups that could represent neurodevelopmental forms of schizophrenia with more homogeneous origins.

Imaging normal and abnormal brain development: new perspectives for child psychiatry

OBJECTIVE

The availability of non-invasive brain imaging permits the study of normal and abnormal brain development in childhood and adolescence. This paper summarizes current knowledge of brain abnormalities of two conditions, attention deficit hyperactivity disorder (ADHD) and childhood onset schizophrenia (COS), and illustrates how such findings are bringing clinical and preclinical perspectives closer together.

METHOD

A selected review is presented of the pattern and temporal characteristics of anatomic brain magnetic resonance imaging (MRI) studies in ADHD and COS. These results are discussed in terms of candidate mechanisms suggested by studies in developmental neuroscience.

RESULTS

There are consistent, diagnostically specific patterns of brain abnormality for ADHD and COS. Attention deficit hyperactivity disorder is characterized by a slightly smaller (4%) total brain volume (both white and grey matter), less-consistent abnormalities of the basal ganglia and a striking (15%) decrease in posterior inferior cerebellar vermal volume. These changes do not progress with age. In contrast, patients with COS have smaller brain volume due to a 10% decrease in cortical grey volume. Moreover, in COS there is a progressive loss of regional grey volume particularly in frontal and temporal regions during adolescence.

CONCLUSIONS

In ADHD, the developmental pattern suggests an early non-progressive 'lesion' involving neurotrophic factors controlling overall brain growth and selected dopamine circuits. In contrast, in COS, which shows progressive grey matter loss, various candidate processes influencing later synaptic and dendritic pruning are suggested by human post-mortem and developmental animal studies.