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

Frequency Dependent Changes of Regional Homogeneity in Children with Growth Hormone Deficiency

Abnormal spontaneous neural activity in children with growth hormone deficiency (GHD) has been found in previous resting-state functional magnetic resonance imaging (rs-fMRI) studies. Nevertheless, the spontaneous neural activity of GHD in different frequency bands is still unclear. Here, we combined rs-fMRI and regional homogeneity (ReHo) methods to analyze the spontaneous neural activity of 26 GHD children and 15 healthy controls (HCs) with age- and sex-matching in four frequency bands: slow-5 (0.014-0.031 Hz), slow-4 (0.031-0.081 Hz), slow-3 (0.081-0.224 Hz), and slow-2 (0.224-0.25 Hz). In the slow-5 band, GHD children compared with HCs displayed higher ReHo in the left dorsolateral part of the superior frontal gyrus, triangular part of the inferior frontal gyrus, precentral gyrus and middle frontal gyrus, and right angular gyrus, while lower ReHo in the right precentral gyrus, and several medial orbitofrontal regions. In the slow-4 band, GHD children relative to HCs revealed increased ReHo in the right middle temporal gyrus, whereas reduced ReHo in the left superior parietal gyrus, right middle occipital gyrus, and bilateral medial parts of the superior frontal gyrus. In the slow-2 band, compared with HCs, GHD children showed increased ReHo in the right anterior cingulate gyrus, and several prefrontal regions, while decreased ReHo in the left middle occipital gyrus, and right fusiform gyrus and anterior cingulate gyrus. Our findings demonstrate that regional brain activity in GHD children exhibits extensive abnormalities, and these abnormalities are related to specific frequency bands, which may provide bases for understanding its pathophysiology significance.

Resting-state functional connectivity in adults with 47,XXX: a 7 Tesla MRI study

Triple X syndrome is a sex chromosomal aneuploidy characterized by the presence of a supernumerary X chromosome, resulting in a karyotype of 47,XXX in affected females. It has been associated with a variable cognitive, behavioral, and psychiatric phenotype, but little is known about its effects on brain function. We therefore conducted 7 T resting-state functional magnetic resonance imaging and compared data of 19 adult individuals with 47,XXX and 21 age-matched healthy control women using independent component analysis and dual regression. Additionally, we examined potential relationships between social cognition and social functioning scores, and IQ, and mean functional connectivity values. The 47,XXX group showed significantly increased functional connectivity of the fronto-parietal resting-state network with the right postcentral gyrus. Resting-state functional connectivity (rsFC) variability was not associated with IQ and social cognition and social functioning deficits in the participants with 47,XXX. We thus observed an effect of a supernumerary X chromosome in adult women on fronto-parietal rsFC. These findings provide additional insight into the role of the X chromosome on functional connectivity of the brain. Further research is needed to understand the clinical implications of altered rsFC in 47,XXX.

Development of prefrontal cortex

During evolution, the cerebral cortex advances by increasing in surface and the introduction of new cytoarchitectonic areas among which the prefrontal cortex (PFC) is considered to be the substrate of highest cognitive functions. Although neurons of the PFC are generated before birth, the differentiation of its neurons and development of synaptic connections in humans extend to the 3rd decade of life. During this period, synapses as well as neurotransmitter systems including their receptors and transporters, are initially overproduced followed by selective elimination. Advanced methods applied to human and animal models, enable investigation of the cellular mechanisms and role of specific genes, non-coding regulatory elements and signaling molecules in control of prefrontal neuronal production and phenotypic fate, as well as neuronal migration to establish layering of the PFC. Likewise, various genetic approaches in combination with functional assays and immunohistochemical and imaging methods reveal roles of neurotransmitter systems during maturation of the PFC. Disruption, or even a slight slowing of the rate of neuronal production, migration and synaptogenesis by genetic or environmental factors, can induce gross as well as subtle changes that eventually can lead to cognitive impairment. An understanding of the development and evolution of the PFC provide insight into the pathogenesis and treatment of congenital neuropsychiatric diseases as well as idiopathic developmental disorders that cause intellectual disabilities.

X-Chromosome Effects on Attention Networks: Insights from Imaging Resting-State Networks in Turner Syndrome

Attention deficit hyperactivity disorder (ADHD) is strongly affected by sex, but sex chromosomes' effect on brain attention networks and cognition are difficult to examine in humans. This is due to significant etiologic heterogeneity among diagnosed individuals. In contrast, individuals with Turner syndrome (TS), who have substantially increased risk for ADHD symptoms, share a common genetic risk factor related to the absence of the X-chromosome, thus serving as a more homogeneous genetic model. Resting-state functional MRI was employed to examine differences in attention networks between girls with TS (n = 40) and age- sex- and Tanner-matched controls (n = 33). We compared groups on resting-state functional connectivity measures from data-driven independent components analysis (ICA) and hypothesis-based seed analysis. Using ICA, reduced connectivity was observed in both frontoparietal and dorsal attention networks. Similarly, using seeds in the bilateral intraparietal sulcus (IPS), reduced connectivity was observed between IPS and frontal and cerebellar regions. Finally, we observed a brain-behavior correlation between IPS-cerebellar connectivity and cognitive attention measures. These findings indicate that X-monosomy contributes affects to attention networks and cognitive dysfunction that might increase risk for ADHD. Our findings not only have clinical relevance for girls with TS, but might also serve as a biological marker in future research examining the effects of the intervention that targets attention skills.

Reversal Learning Performance in the XY∗ Mouse Model of Klinefelter and Turner Syndromes

Klinefelter syndrome (KS; 47, XXY) and Turner syndrome (TS; 45, XO) are caused by two relatively common sex chromosome aneuploidies. These conditions are associated with an increased odds of neuropsychiatric disorders, including attention deficit/hyperactivity disorder (ADHD), as well as impairments in cognition that include learning delays, attentional dysfunction and impulsivity. We studied cognitive functions in the XY^∗ mouse model, which allows comparison of XXY to XY males (KS model), and XO to XX females (TS model). We evaluated adult mice with and without gonads, using a version of an operant reversal-learning task (RLT) that can be used to measure various facets of learning, impulsivity and attention. In the KS model, only one measure related to impulsivity – perseverative responding under reversal conditions – reliably discriminated gonadally intact XXY and XY mice. In contrast, a fundamental learning impairment (more trials to criterion in acquisition phase) in XXY mice, as compared to XY, was observed in gonadectomized subjects. No other task measures showed differences consistent with KS. In the TS mouse model, XO mice did not show a pattern of results consistent with TS, similar to past observations. Thus, the application of this RLT to these XY^∗ models reveals only limited behavioral impairments relevant to KS.

Sex differences in psychiatric disorders: what we can learn from sex chromosome aneuploidies

The study of sexual dimorphism in psychiatric and neurodevelopmental disorders is challenging due to the complex interplay of diverse biological, psychological, and social factors. Males are more susceptible to neurodevelopmental disorders including intellectual disability, autism spectrum disorder, and attention-deficit activity disorder. Conversely, after puberty, females are more prone to major depressive disorder and anxiety disorders compared to males. One major biological factor contributing to sex differences is the sex chromosomes. First, the X and Y chromosomes have unique and specific genetic effects as well as downstream gonadal effects. Second, males have one X chromosome and one Y chromosome, while females have two X chromosomes. Thus, sex chromosome constitution also differs between the sexes. Due to this complexity, determining genetic and downstream biological influences on sexual dimorphism in humans is challenging. Sex chromosome aneuploidies, such as Turner syndrome (X0) and Klinefelter syndrome (XXY), are common genetic conditions in humans. The study of individuals with sex chromosome aneuploidies provides a promising framework for studying sexual dimorphism in neurodevelopmental and psychiatric disorders. Here we will review and contrast four syndromes caused by variation in the number of sex chromosomes: Turner syndrome, Klinefelter syndrome, XYY syndrome, and XXX syndrome. Overall we describe an increased rate of attention-deficit hyperactivity disorder and autism spectrum disorder, along with the increased rates of major depressive disorder and anxiety disorders in one or more of these conditions. In addition to contributing unique insights about sexual dimorphism in neuropsychiatric disorders, awareness of the increased risk of neurodevelopmental and psychiatric disorders in sex chromosome aneuploidies can inform appropriate management of these common genetic disorders.

Attention deficit hyperactivity disorder (ADHD) in phenotypically similar neurogenetic conditions: Turner syndrome and the RASopathies

Background

ADHD (attention deficit hyperactivity disorder) is a common neurodevelopmental disorder. There has been extensive clinical and basic research in the field of ADHD over the past 20 years, but the mechanisms underlying ADHD risk are multifactorial, complex and heterogeneous and, as yet, are poorly defined. In this review, we argue that one approach to address this challenge is to study well-defined disorders to provide insights into potential biological pathways that may be involved in idiopathic ADHD.

Main body

To address this premise, we selected two neurogenetic conditions that are associated with significantly increased ADHD risk: Turner syndrome and the RASopathies (of which Noonan syndrome and neurofibromatosis type 1 are the best-defined with regard to ADHD-related phenotypes). These syndromes were chosen for two main reasons: first, because intellectual functioning is relatively preserved, and second, because they are strikingly phenotypically similar but are etiologically distinct. We review the cognitive, behavioural, neural and cellular phenotypes associated with these conditions and examine their relevance as a model for idiopathic ADHD.

Conclusion

We conclude by discussing current and future opportunities in the clinical and basic research of these conditions, which, in turn, may shed light upon the biological pathways underlying idiopathic ADHD.

Mapping the effect of the X chromosome on the human brain: Neuroimaging evidence from Turner syndrome

In addition to determining sex, the X chromosome has long been considered to play a crucial role in brain development and intelligence. Turner syndrome (TS) is caused by the congenital absence of all or part of one of the X chromosomes in females. Thus, Turner syndrome provides a unique "knock-out model" for investigating how the X chromosome influences the human brain in vivo. Numerous cutting-edge neuroimaging techniques and analyses have been applied to investigate various brain phenotypes in women with TS, which have yielded valuable evidence toward elucidating the causal relationship between the X chromosome and human brain structure and function. In this review, we comprehensively summarize the recent progress made in TS-related neuroimaging studies and emphasize how these findings have enhanced our understanding of X chromosome function with respect to the human brain. Future investigations are encouraged to address the issues of previous TS neuroimaging studies and to further identify the biological mechanisms that underlie the function of specific X-linked genes in the human brain.

Chiari I Malformation Associated with Turner Syndrome

Turner syndrome (TS) is a rare genetic disease due to the absence of one X chromosome. Patients with TS have more subtle neurological/neuropsychiatric problems, while headache is an uncommon clinical presentation which needs attention. We report a 12-year-old child presenting with typical cough headache. Her magnetic resonance imaging revealed Chiari I malformation associated with TS. To the best of our knowledge, Chiari I malformation associated with TS is not described in literature. We report the first case of TS associated with Chiari I malformation. Interestingly, Chiari I malformation is also associated with Noonan's syndrome, which is a close morphological mimicker of TS, raising the possibility of sharing similar pathogenesis in both conditions.

The role of short-term memory and visuo-spatial skills in numerical magnitude processing: Evidence from Turner syndrome

Most studies on magnitude representation have focused on the visual modality with no possibility of disentangling the influence of visuo-spatial skills and short-term memory (STM) abilities on quantification processes. This study examines this issue in patients with Turner syndrome (TS), a genetic condition characterized by a specific cognitive profile frequently associating poor mathematical achievement, low spatial skills and reduced STM abilities. In order to identify the influence of visuo-spatial and STM processing on numerical magnitude abilities, twenty female participants with TS and twenty control female participants matched for verbal IQ and education level were administered a series of magnitude comparison tasks. The tasks differed on the nature of the magnitude to be processed (continuous, discrete and symbolic magnitude), on visuo-spatial processing requirement (no/high) and on STM demands (low in simultaneous presentation vs. high in sequential presentation). Our results showed a lower acuity when participants with TS compared the numerical magnitudes of stimuli presented sequentially (low visuo-spatial processing and high STM load: Dot sequence and Sound sequence) while no difference was observed in the numerical comparison of sets presented simultaneously. In addition, the group difference in sequential tasks disappeared when controlling for STM abilities. Finally, both groups demonstrated similar performance when comparing continuous or symbolic magnitude stimuli and they exhibited comparable subitizing abilities. These results highlight the importance of STM abilities in extracting numerosity through a sequential presentation and underline the importance of considering the impact of format presentation on magnitude judgments.

The Effects of the X Chromosome on Intrinsic Functional Connectivity in the Human Brain: Evidence from Turner Syndrome Patients

Turner syndrome (TS), a disorder caused by the congenital absence of one of the 2 X chromosomes in female humans, provides a valuable human "knockout model" for studying the functions of the X chromosome. At present, it remains unknown whether and how the loss of the X chromosome influences intrinsic functional connectivity (FC), a fundamental phenotype of the human brain. To address this, we performed resting-state functional magnetic resonance imaging and specific cognitive assessments on 22 TS patients and 17 age-matched control girls. A novel data-driven approach was applied to identify the disrupted patterns of intrinsic FC in TS. The TS girls exhibited significantly reduced whole-brain FC strength within the bilateral postcentral gyrus/intraparietal sulcus, angular gyrus, and cuneus and the right cerebellum. Furthermore, a specific functional subnetwork was identified in which the intrinsic FC between nodes was mostly reduced in TS patients. Particularly, this subnetwork is composed of 3 functional modules, and the disruption of intrinsic FC within one of these modules was associated with the deficits of TS patients in math-related cognition. Taken together, these findings provide novel insight into how the X chromosome affects the human brain and cognition, and emphasize an important role of X-linked genes in intrinsic neural coupling.

Alterations in brain connectivity in three sub-regions of the anterior cingulate cortex in heroin-dependent individuals: Evidence from resting state fMRI

Previous studies that utilized task-based approaches have demonstrated that the chronic use of heroin is associated with altered activity of the anterior cingulate cortex (ACC). However, few studies have focused on examining the variation in resting-state functional connectivity in heroin-dependent individuals, which might help further understanding the mechanisms underlying heroin addiction. Due to the structural and functional heterogeneity of the ACC, we systematically mapped the resting-state functional connectivity patterns of three sub-regions of the ACC in heroin-dependent individuals, wondered whether the partition of three sub-regions of the ACC is feasible in heroin-dependent individuals, and identified how heroin affected the correlated activities among three sub-regions of the ACC using resting-state functional magnetic resonance imaging (fMRI). In the present study, fMRI data were acquired from 21 heroin-dependent individuals (Her group) and 15 non-addicted controls (CN group). Compared to controls, there were reduced functional connectivities in the dorsal ACC (dACC) and rostral ACC (rACC) networks with different areas of the dorsal striatum (the caudate and the putamen) in the Her group. Meanwhile, there exhibited an inverted alteration of pattern for orbital frontal cortex (OFC) and superior frontal gyrus (SFG) in the functional connectivity network with the dACC and subcallosal ACC (sACC), and a different alteration of the cerebellum and the amygdala in the functional connectivity network with the rACC and the sACC. In addition, we also found reduced connectivities between dACC and rACC, as well as reduced connectivities between sACC and dACC. Our findings of variations of functional connectivities in three sub-regions of ACC in Her group implied that these sub-regions of the ACC together with other key brain areas (such as dorsal striatum, OFC, SFG, cerebellum, amygdale, etc.) might potentially play independent and/or overlapping roles in heroin addiction, which might indicate the potential direction of future research.

Turner syndrome: review of clinical, neuropsychiatric, and EEG status: an experience of tertiary center

We reviewed the clinical, neuropsychiatric, and EEG status of 53 turner syndrome (TS) females, aged 3-16 years, in Assiut university hospitals, Upper Egypt. The diagnosis and care of patients with TS in Egypt is still in the developing stage. Hence this study was undertaken to review the details of patients with TS with respect to the pattern of cognitive, psychiatric, and motor dysfunction. We aimed to provide a comprehensive data about the experience of our center comparable to previous studies, which have been published in this field. This will contribute to a better definition of the neuropsychiatric features that may be specific to TS that allows early and better detection and management of these cases. We found FSIQ and verbal IQ that seem to be at a nearly normal level and a decreased performance IQ. ADHD and autistic symptoms were found in 20.70 and 3.77 % of our cohort, respectively. The motor performance in TS was disturbed, with some neurological deficits present in 17 % (reduced muscle tone and reduced muscle power). In addition, females with TS in our study exhibit social and emotional problems, including anxiety (5.66 %) and depression (11.30 %). The EEG results revealed abnormalities in seven patients (13.20 %). One patient presenting with generalized tonic-clonic seizures showed generalized epileptiform activity, and six patients presenting with intellectual disabilities showed abnormal EEG background activity.

Exceptional lexical skills but executive language deficits in school starters and young adults with Turners syndrome: implications for X chromosome effects on brain function

TS school starters had enhanced receptive and expressive language on standardised assessment (CELF-P) and enhanced rhyme judgements, spoonerisms, and lexical decision, indicating enhanced phonological skills and word representations. There was marginal but consistent advantage across lexico-semantic tasks. On executive tasks, speeded naming of numbers was impaired but not pictures. Young TS adults had enhanced naming and receptive vocabulary, indicating enhanced semantic skills. There were consistent deficits in executive language: phonemic oral fluency, rhyme fluency, speeded naming of pictures, numbers and colours; sentence completion requiring supression of prepotent responses. Haploinsufficiency of X-chromosome drives mechanisms that affect the anatomical and neurochemical development of the brain, resulting in enhanced temporal lobe aspects of language. These strengths co-exist with impaired development of frontal lobe executive language systems. This means not only that these elements of language can decouple in development but that their very independence is driven by mechanisms linked to the X-chromosome.

Reduced functional connectivity during working memory in Turner syndrome

Turner syndrome (TS) is a genetic disorder affecting females, resulting from the complete or partial absence of an X chromosome. The cognitive profile of TS shows relative strengths in the verbal domain and weaknesses in the procedural domain, including working memory. Neuroimaging studies have identified differences in the morphology of the parietal lobes, and white matter pathways linking frontal and parietal regions, as well as abnormal activation in dorsal frontal and parietal regions. Taken together these findings suggest that abnormal functional connectivity between frontal and parietal regions may be related to working memory impairments in TS, a hypothesis we tested in the present study. We scanned TS and typically developing participants with functional magnetic resonance imaging while they performed visuospatial and phonological working memory tasks. We generated a seed region in parietal cortex based on structural differences in TS and found that functional connectivity with dorsal frontal regions was reduced during working memory in TS. Finally, we found that connectivity was correlated with task performance in TS. These findings suggest that structural brain abnormalities in TS affect not only regional activity but also the functional interactions between regions and that this has important consequences for behavior.

Response inhibition and reward anticipation in medication-naïve adults with attention-deficit/hyperactivity disorder: a within-subject case-control neuroimaging study

BACKGROUND

Previous research suggests that ADHD patients are characterized by both reduced activity in the inferior frontal gyrus (IFG) during response inhibition tasks (such as the Go-NoGo task), and reduced activity in the ventral striatum during reward anticipation tasks (such as the Monetary-Incentive-Delay [MID] task). However, no prior research has applied either of these paradigms in medication-naïve adults with ADHD, nor have these been implemented in an intrasubject manner.

METHODS

The sample consisted of 19 medication-naïve adults with ADHD and 19 control subjects. Main group analyses were based on individually defined regions of interest: the IFG and the VStr for the Go-NoGo and the MID task respectively. In addition, we analyzed the correlation between the two measures, as well as between these measures and the clinical symptoms of ADHD.

RESULTS

We observed reduced bilateral VStr activity in adults with ADHD during reward anticipation. No differences were detected in IFG activation on the Go-NoGo paradigm. Correlation analyses suggest that the two tasks are independent at a neural level, but are related behaviorally in terms of the variability of the performance reaction time. Activity in the bilateral VStr but not in the IFG was associated negatively with symptoms of hyperactivity/impulsivity.

CONCLUSIONS

Results underline the implication of the reward system in ADHD adult pathophysiology and suggest that frontal abnormalities during response inhibition performance may not be such a pivotal aspect of the phenotype in adulthood. In addition, our findings point toward response variability as a core feature of the disorder.

Neuroanatomical spatial patterns in Turner syndrome

Turner syndrome (TS) is a highly prevalent genetic condition caused by partial or complete absence of one X-chromosome in a female and is associated with a lack of endogenous estrogen during development secondary to gonadal dysgenesis. Prominent cognitive weaknesses in executive and visuospatial functions in the context of normal overall IQ also occur in affected individuals. Previous neuroimaging studies of TS point to a profile of neuroanatomical variation relative to age and sex matched controls. However, there are no neuroimaging studies focusing on young girls with TS before they receive exogenous estrogen treatment to induce puberty. Information obtained from young girls with TS may help to establish an early neural correlate of the cognitive phenotype associated with the disorder. Further, univariate analysis has predominantly been the method of choice in prior neuroimaging studies of TS. Univariate approaches examine between-group differences on the basis of individual image elements (i.e., a single voxel's intensity or the volume of an a priori defined brain region). This is in contrast to multivariate methods that can elucidate complex neuroanatomical profiles in a clinical population by determining the pattern of between-group differences from many image elements evaluated simultaneously. In this case, individual image elements might not be significantly different between groups but can still contribute to a significantly different overall spatial pattern. In this study, voxel-based morphometry (VBM) of high-resolution magnetic resonance images was used to investigate differences in brain morphology between 13 pediatric, pre-estrogen girls with monosomic TS and 13 age-matched typically developing controls (3.0 T imaging: mean age 9.1±2.1). A similar analysis was performed with an older cohort of 13 girls with monosomic TS and 13 age-matched typically developing controls (1.5 T imaging: mean age 15.8±4.5). A multivariate, linear support vector machine analysis using leave-one-out cross-validation was then employed to discriminate girls with TS from typically developing controls based on differences in neuroanatomical spatial patterns and to assess how accurately such patterns translate across heterogeneous cohorts. VBM indicated that both TS cohorts had significantly reduced gray matter volume in the precentral, postcentral, and supramarginal gyri and enlargement of the left middle and superior temporal gyri. Support vector machine (SVM) classifiers achieved high accuracy for discriminating brain morphology patterns in TS from typically developing controls and also displayed spatial patterns consistent with the VBM results. Furthermore, the SVM classifiers identified additional neuroanatomical variations in individuals with TS, localized in the hippocampus, orbitofrontal cortex, insula, caudate, and cuneus. Our results demonstrate robust spatial patterns of altered brain morphology in developmentally dynamic populations with TS, providing further insight into the neuroanatomical correlates of cognitive-behavioral features in this condition.

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.

Cortical anatomy in human X monosomy

Turner syndrome (TS) is a model for X chromosome influences on neurodevelopment because it is most commonly caused by absence of one X chromosome and associated with altered brain structure and function. However, all prior in vivo magnetic resonance imaging studies of the brain in TS have either used manual approaches or voxel-based morphometry (VBM) to measure cortical volume (CV). These methods, unlike surface-based morphometry (SBM), cannot measure the two neurobiologically distinct determinants of CV- cortical thickness (CT) and surface area (SA) - which have differing genetic determinants and may be independently altered. Therefore, in 24 adults with X monosomy and 19 healthy female controls, we used SBM to compare (i) lobar CV, CT and SA; (ii) an index of hemispheric gyrification; (iii) CT throughout the cortical sheet; and (iv) CT correlation between cortical regions. Compared to controls, females with TS had (i) significantly increased CT and decreased SA in parietal and occipital lobes (resulting in no significant difference in lobar CV); (ii) reduced hemispheric gyrification bilaterally; (iii) foci of significantly increased CT involving inferior temporal, lateral occipital, intraparietal sulcus (IPS), cingulate and orbitofrontal cortices; and (iv) significantly reduced CT correlation between the left IPS and cortical regions including supramarginal and lateral occipital gyri. Our findings suggest that females with TS have complex, sometimes "opposing", abnormalities in SA/gyrification (decreased) and CT (increased), which can result in no overall detectable differences in CV. Thus, haploinsufficiency of X chromosome genes, may differentially impact the distinct mechanisms shaping SA (e.g. cortical folding) and CT (e.g. dendritic arborization/pruning). CT disruptions are maximal within and between cortical regions previously implicated in the TS cognitive phenotype.

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.

Vulnerabilidad social en el síndrome de turner: interacción genes-ambiente

En este trabajo se exponen los fundamentos teóricos que permiten considerar al Síndrome de Turner como un “modelo genético sensible” en el cual analizar asociaciones entre caracteres psicológicos y factores genéticos y ambientales. La investigación en esta línea permitiría dilucidar mecanismos de riesgo ambiental y comprender el grado de “vulnerabilidad” que presentan las mujeres con el síndrome. El Síndrome de Turner es un trastorno genético, no heredable, que se caracteriza por la deleción total o parcial del cromosoma X en el sexo femenino. El estudio de la disfunción social que presentan las mujeres con este síndrome, es decir, de la capacidad para relacionarse con el entorno y la calidad de los vínculos tiene importantes implicaciones en la comprensión de la forma en que actúa el ambiente sobre el desarrollo psicológico, y de cómo a su vez éste se ve afectado por factores genéticos que actúan en interacción.

Moving toward an understanding of hormone replacement therapy in adolescent girls: looking through the lens of Turner syndrome

Turner syndrome (TS) is a relatively common disorder of phenotypic females caused by loss of all or part of the second sex chromosome. Most individuals with TS have short stature and gonadal dysgenesis and are at risk for many other medical and learning problems. In the 45,X ovary, germs cells multiply quite normally during fetal development, but there is accelerated atresia of oocytes in the second half of pregnancy that produces gonadal insufficiency by birth. In girls with other karyotypes, especially those mosaic for 45,X/46,XX, gonadal function may be normal or near-normal. In this chapter, management goals for gonadal insufficiency in girls with TS are presented. The effects of estrogen deficiency and its replacement on three specific problems associated with TS-short stature, cardiovascular disease, and developmental differences in brain structure and function-are explored. General guidelines for estrogen replacement therapy using transdermal estrogen, the most physiologic option, are provided and future research goals are outlined.

Impaired response inhibition function in abstinent heroin dependents: an fMRI study

Heroin, like various illicit substances, has a negative impact on the frontal cognitive function after repeated abuse. We used functional magnetic resonance imaging (fMRI) to examine the neural substrates of response inhibition and competition in 18 healthy controls and assess the frontal neurocognition in 30 abstinent heroin dependents (AHD) as they performed a Go/NoGo Association task with reaction times recorded spontaneously. The neural response which was induced by response inhibition was prominent in the midline structure, specifically the bilateral medial prefrontal gyrus and anterior cingulated cortex, as well as the left middle frontal gyrus, insula, bilateral inferior frontal gyrus and limbic system. Unlike drug-naïve controls, only the bilateral superior frontal gyrus and left middle frontal gyrus were activated in AHD. Furthermore, the RT of AHD was significantly longer than that of controls. The results suggest that: (1) the ACC, mPFC and inferior frontal lobe play an important role in response inhibition and competition; (2) heroin dependents had an impaired response inhibition function that lasted even months into abstinence, which indicates that the negative effect of heroin on the inhibitory function still continues in early protracted withdrawal state.

Turner Syndrome

Turner syndrome is a neurogenetic disorder characterized by partial or complete monosomy-X. It is associated with certain physical and medical features, including estrogen deficiency, short stature, and increased risk for several diseases, with cardiac conditions being among the most serious. The cognitive-behavioral phenotype associated with the syndrome includes strengths in verbal domains with impairments in visuospatial, executive function, and emotion processing. Less is known regarding psychosocial and psychiatric functioning in Turner syndrome, but essential aspects of psychotherapeutic treatment plans are suggested. Future investigations should include continued genetic studies and determination of candidate genes for physical and cognitive features. Multimodal, interdisciplinary studies are essential for identifying optimal, syndrome-specific interventions for improving the lives of individuals who have Turner syndrome.

Ocular motor indicators of executive dysfunction in fragile X and Turner syndromes

Fragile X and Turner syndromes are two X-chromosome-related disorders associated with executive function and visual spatial deficits. In the present study, we used ocular motor paradigms to examine evidence that disruption to different neurological pathways underlies these deficits. We tested 17 females with fragile X, 19 females with Turner syndrome, and 40 females with neither disorder who comprised the comparison group. Group differences emerged for both the fragile X and Turner syndrome groups, each relative to the comparison group: Females with fragile X had deficits in generating memory-guided saccades, predictive saccades, and saccades made in the overlap condition of a gap/overlap task. Females with Turner syndrome showed deficits in generating memory-guided saccades, but not during either the predictive saccade or gap/overlap task. Females with Turner syndrome, but not females with fragile X, showed deficits in visually guided saccades and anti-saccades. These findings indicate that different brain regions are affected in the two disorders, and suggest that different pathways lead to the similar cognitive phenotypes described for fragile X and Turner syndromes.

It is not all hormones: Alternative explanations for sexual differentiation of the brain

Males and females of many species differ with regard to neurodevelopment, ongoing brain function and behavior. For many years, it was assumed that these differences primarily arose due to hormonal masculinization of the male brain (and to a lesser extent hormonal feminization of the female brain). Recent elegant experiments in model systems have revealed that, while gonadal hormones undoubtedly play an important role in sexual differentiation of the brain, they are not the only possible mechanism for this phenomenon. In the present review, we discuss the concept that genes residing upon the sex chromosomes (which are asymmetrically inherited between males and females) may influence sexually dimorphic neurobiology directly, and suggest possible mechanisms. Future work will be directed towards understanding the extent and specificity with which sex-linked genes and hormones define brain structure and function, and towards elucidating potential interactions between the two mechanisms. Ultimately, it is hoped that such studies will provide insights into why men and women are differentially vulnerable to certain mental disorders, and will enable the development of effective sex-tailored therapeutics.

Healthcare for adolescents with Turner syndrome

This review paper highlights important healthcare issues for adolescents with Turner Syndrome. Turner Syndrome potentially affects multiple organ systems including: cardiovascular, renal, endocrine, neurologic, gastrointestinal, skin, skeletal, auditory, and reproductive systems. Congenital and acquired cardiac defects remain the most significant health problem faced by women with Turner Syndrome.

Selective alterations of white matter associated with visuospatial and sensorimotor dysfunction in turner syndrome

Turner syndrome (TS) is a neurogenetic disorder characterized by impaired spatial, numerical, and motor functioning but relatively spared verbal ability. Results from previous neuroimaging studies suggest that gray matter alterations in parietal and frontal regions may contribute to atypical visuospatial and executive functioning in TS. Recent findings in TS also indicate variations in the shape of parietal gyri and white matter microstructural anomalies of the temporal lobe. Diffusion tensor imaging and structural imaging methods were used to determine whether 10 females with TS and 10 age- and gender-matched control subjects exhibited differences in fractional anisotropy, white matter density, and local brain shape. Relative to controls, females with TS had lower fractional anisotropy (FA) values in the deep white matter of the left parietal-occipital region extending anteriorly along the superior longitudinal fasciculus into the deep white matter of the frontal lobe. In addition, decreased FA values were located bilaterally in the internal capsule extending into the globus pallidus and in the right prefrontal region. Voxel-based morphometry (VBM) analysis showed corresponding white matter density differences in the internal capsules and left centrum semiovale. Tensor-based morphometry analysis indicated that the FA and VBM results were not attributable to differences in the local shape of brain structures. Compared with controls, females with TS had increases in FA values and white matter density in language-related areas of the inferior parietal and temporal lobes. These complementary analyses provide evidence for alterations in white matter pathways that subserve affected and preserved cognitive functions in TS.

Visuospatial skills and their association with math performance in girls with fragile X or Turner syndrome

The present study was designed to assess object identification ("what") and location ("where") skills among girls with fragile X or Turner syndrome and girls with neither disorder. Participants completed standardized subtests of visual perception and tasks of visuospatial "what" and "where" memory. Girls with fragile X had average performance on most object identification tasks, yet 53% failed to accurately recreate the gestalt of a design during the "where" memory task. Fewer than 7% of girls in the Turner or comparison group made this error. Girls with Turner syndrome had lower scores and longer response times on object perception tasks and had poorer recall of location for internal features of the design on the "where" memory task, relative to girls in the comparison or fragile X group. When limiting analyses to IQ-matched samples, correlations between math and visual perception tasks emerged, but only for girls with fragile X. These results reflect important differences between two cognitive phenotypes and have implications for the role of visuospatial processing in early math performance.

Visuospatial executive function in Turner syndrome: functional MRI and neurocognitive findings

Turner syndrome is a genetic disorder that results from an abnormal or missing X chromosome in females and is typically associated with impairments in visuospatial, but not verbal, information processing. These visuospatial processing impairments may be exacerbated with increased task demands, such as those engaged during working memory (WM). While previous studies have examined spatial WM function in Turner syndrome, none have directly compared the neural correlates of spatial and verbal WM processes across the encoding, maintenance and retrieval phases. We employed both neurocognitive assessments and functional MRI (fMRI) to examine the neural circuitry underlying both verbal and visuospatial WM functions in individuals with Turner syndrome and normal controls. We furthermore examined the vulnerability of task-related fMRI activation to distracters presented during WM maintenance. Fifteen healthy female volunteers and eight individuals with Turner syndrome performed a delayed-response WM task during fMRI scanning. Neurocognitive tests revealed impaired performance across both verbal and spatial domains in Turner syndrome, with greater impairment on tasks with WM demands. Frontoparietal regions in controls showed significantly sustained levels of activation during visuospatial WM. This sustained activation was significantly reduced in the group with Turner syndrome. Domain-specific activation of temporal regions, in contrast, did not differ between the two groups. Sensory distraction during the WM maintenance phase did not differentially alter frontoparietal activation between the two groups. The results reveal impaired frontoparietal circuitry recruitment during visuospatial executive processing in Turner syndrome, suggesting a significant role for the X chromosome in the development of these pathways.

Neuro-functional differences associated with arithmetic processing in Turner syndrome

Turner syndrome (TS) is a neurogenetic disorder characterized by the absence of one X chromosome in a phenotypic female. Individuals with TS are at risk for impairments in mathematics. We investigated the neural mechanisms underlying arithmetic processing in TS. Fifteen subjects with TS and 15 age-matched typically developing controls were scanned using functional MRI while they performed easy (two-operand) and difficult (three-operand) versions of an arithmetic processing task. Both groups activated fronto-parietal regions involved in arithmetic processing during the math tasks. Compared with controls, the TS group recruited additional neural resources in frontal and parietal regions during the easier, two-operand math task. During the more difficult three-operand task, individuals with TS demonstrated significantly less activation in frontal, parietal and subcortical regions than controls. However, the TS group's performance on both math tasks was comparable to controls. Individuals with TS demonstrate activation differences in fronto-parietal areas during arithmetic tasks compared with controls. They must recruit additional brain regions during a relatively easy task and demonstrate a potentially inefficient response to increased task difficulty compared with controls.

X-linked imprinting: effects on brain and behaviour

Imprinted genes are monoallelically expressed in a parent-of-origin-dependent manner and can affect brain and behavioural phenotypes. The X chromosome is enriched for genes affecting neurodevelopment and is donated asymmetrically to male and female progeny. Hence, X-linked imprinted genes could potentially influence sexually dimorphic neurobiology. Consequently, investigations into such loci may provide new insights into the biological basis of behavioural differences between the sexes and into why men and women show different vulnerabilities to certain mental disorders. In this review, we summarise recent advances in our knowledge of X-linked imprinted genes and the brain substrates that they may act upon. In addition, we suggest strategies for identifying novel X-linked imprinted genes and their downstream effects and discuss evolutionary theories regarding the origin and maintenance of X-linked imprinting.

Endocrine disruption and cognitive function in adolescent female rhesus monkeys

Female rhesus monkeys (n=8/group) received daily oral doses of exogenous estrogen [diethylstilbestrol (DES), 0.5 mg/kg, methoxychlor (MXC), 25 or 50 mg/kg] for 6 months before and after the anticipated age of menarche. Behavior was assessed during and for 9 months after dosing. Visual discrimination performance (simultaneous nonmatch-to-sample with trial-unique stimuli) conducted during dosing demonstrated delayed improvement and poorer performance in the MXC50 group, with some similar effects in the DES group. Visual recognition memory, assessed with delays of < or = 3 s, was not apparently affected. Spatial working memory, assessed after dosing, also showed acquisition deficits and possible working memory difficulties in the MXC50 group. Spontaneous motor activity, monitored at 6-month intervals, was not affected by treatment. Late peak latencies of the auditory brainstem response (ABR) were shorter in the DES group 6 months after treatment, suggesting long-term effects on brain. The study suggests that some aspects of brain function can be modified by exposure to exogenous estrogen during pubertal development. Although DES is a more potent estrogen, the high-dose MXC group was more affected behaviorally. Differential effects of the two agents at the estrogen receptor subtypes (ER alpha and ER beta) may be relevant to the differential behavioral outcomes.

Effects of prenatal marijuana on response inhibition: an fMRI study of young adults

The neurophysiological effects of prenatal marijuana exposure on response inhibition were assessed in 18- to 22-year-olds. Thirty-one participants from the Ottawa Prenatal Prospective Study (OPPS) performed a blocked design Go/No-Go task while neural activity was imaged with functional magnetic resonance imaging (fMRI). The OPPS is a longitudinal study that provides a unique body of information collected from each participant over 20 years, including prenatal drug history, detailed cognitive/behavioral performance from infancy to young adulthood, and current and past drug usage. The fMRI results showed that with increased prenatal marijuana exposure, there was a significant increase in neural activity in bilateral prefrontal cortex and right premotor cortex during response inhibition. There was also an attenuation of activity in left cerebellum with increased prenatal exposure to marijuana when challenging the response inhibition neural circuitry. Prenatally exposed offspring had significantly more commission errors than nonexposed participants, but all participants were able to perform the task with more than 85% accuracy. These findings were observed when controlling for present marijuana use and prenatal exposure to nicotine, alcohol and caffeine, and suggest that prenatal marijuana exposure is related to changes in neural activity during response inhibition that last into young adulthood.

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.

Amygdala and hippocampal volumes in Turner syndrome: a high-resolution MRI study of X-monosomy

Turner syndrome (TS) results from partial or complete X-monosomy and is characterized by deficits in visuospatial functioning as well as social cognition and memory. Neuroimaging studies have demonstrated volumetric differences in the parietal region of females with TS compared to controls. The present study examined amygdala and hippocampus morphology in an attempt to further understand the neural correlates of psychosocial and memory functioning in TS. Thirty females with TS age 7.6-33.3 years (mean = 14.7 +/- 6.4) and 29 age-matched controls (mean age = 14.8 +/- 5.9; range = 6.4-32.7) were scanned using high resolution MRI. Volumetric analyses of the MRI scans included whole brain segmentation and manual delineation of the amygdala and hippocampus. Compared to controls, participants with TS demonstrated significantly larger left amygdala gray matter volumes, irrespective of total cerebral tissue and age. Participants with TS also showed disproportionately reduced right hippocampal volumes, involving both gray and white matter. Amygdala and hippocampal volumes appear to be impacted by X-monosomy. Aberrant morphology in these regions may be related to the social cognition and memory deficits often experienced by individuals with TS. Further investigations of changes in medial temporal morphology associated with TS are warranted.

A review of neuropsychological and motor studies in Turner Syndrome

We reviewed the literature on Turner Syndrome (TS) from 1962 until March 2003 with respect to the following questions: Is there a consistent pattern of cognitive and/or motor dysfunction in TS girls and if so, is there an explanation for the disturbance? Many studies indicate that girls with TS have a disharmonic IQ profile: a verbal IQ that seems to be at a (nearly) normal level and a decreased PIQ. This profile remains into adulthood. Visual-spatial problems are mentioned most frequently and there is some evidence for a relationship to particular neuro-anatomical structures, hormonal dysfunction, and genotype. Although much less research has been done on motor performance in TS, there is clear evidence that it is disturbed too in TS. Many authors emphasize the interaction between somatic, psychological and social factors, but we did not find a clear theoretical framework explaining this relationship. We argue that there may be two independent problems: a visuospatial and a motor deficit possible related to specific genotypes and both have implications for functioning in daily life.