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

Syndrome-Specific Neuroanatomical Phenotypes in Girls With Turner and Noonan Syndromes

BACKGROUND

Turner syndrome (TS) and Noonan syndrome (NS) are distinct genetic conditions with highly similar physical and neurodevelopmental phenotypes. TS is caused by X chromosome absence, whereas NS results from genetic mutations activating the Ras-mitogen-activated protein kinase signaling pathway. Previous neuroimaging studies in individuals with TS and NS have shown neuroanatomical variations relative to typically developing individuals, a standard comparison group when initially examining a clinical group of interest. However, none of these studies included a second clinical comparison group, limiting their ability to identify syndrome-specific neuroanatomical phenotypes.

METHODS

In this study, we compared the behavioral and brain phenotypes of 37 girls with TS, 26 girls with NS, and 37 typically developing girls, all ages 5 to 12 years, using univariate and multivariate data-driven analyses.

RESULTS

We found divergent neuroanatomical phenotypes between groups, despite high behavioral similarities. Relative to the typically developing group, TS was associated with smaller whole-brain cortical surface area (p ≤ .0001), whereas NS was associated with smaller whole-brain cortical thickness (p = .013). TS was associated with larger subcortical volumes (left amygdala, p = .002; right hippocampus, p = .002), whereas NS was associated with smaller subcortical volumes (bilateral caudate, p ≤ .003; putamen, p < .001; pallidum, p < .001; right hippocampus, p = .015). Multivariate analyses also showed diverging brain phenotypes in terms of surface area and cortical thickness, with surface area outperforming cortical thickness at group separation.

CONCLUSIONS

TS and NS have syndrome-specific brain phenotypes, despite their behavioral similarities. Our observations suggest that neuroanatomical phenotypes better reflect the different genetic etiologies of TS and NS and may be superior biomarkers relative to behavioral phenotypes.

Adolescent brain development in girls with Turner syndrome

Turner syndrome (TS) is a common sex chromosome aneuploidy in females associated with various physical, cognitive, and socio-emotional phenotypes. However, few studies have examined TS-associated alterations in the development of cortical gray matter volume and the two components that comprise this measure-surface area and thickness. Moreover, the longitudinal direct (i.e., genetic) and indirect (i.e., hormonal) effects of X-monosomy on the brain are unclear. Brain structure was assessed in 61 girls with TS (11.3 ± 2.8 years) and 55 typically developing girls (10.8 ± 2.3 years) for up to 4 timepoints. Surface-based analyses of cortical gray matter volume, thickness, and surface area were conducted to examine the direct effects of X-monosomy present before pubertal onset and indirect hormonal effects of estrogen deficiency/X-monosomy emerging after pubertal onset. Longitudinal analyses revealed that, whereas typically developing girls exhibited normative declines in gray matter structure during adolescence, this pattern was reduced or inverted in TS. Further, girls with TS demonstrated smaller total surface area and larger average cortical thickness overall. Regionally, the TS group exhibited decreased volume and surface area in the pericalcarine, postcentral, and parietal regions relative to typically developing girls, as well as larger volume in the caudate, amygdala, and temporal lobe regions and increased thickness in parietal and temporal regions. Surface area alterations were predominant by age 8, while maturational differences in thickness emerged by age 10 or later. Taken together, these results suggest the involvement of both direct and indirect effects of X-chromosome haploinsufficiency on brain development in TS.

Organ Abnormalities Caused by Turner Syndrome

Turner syndrome (TS), a genetic disorder due to incomplete dosage compensation of X-linked genes, affects multiple organ systems, leading to hypogonadotropic hypogonadism, short stature, cardiovascular and vascular abnormalities, liver disease, renal abnormalities, brain abnormalities, and skeletal problems. Patients with TS experience premature ovarian failure with a rapid decline in ovarian function caused by germ cell depletion, and pregnancies carry a high risk of adverse maternal and fetal outcomes. Aortic abnormalities, heart defects, obesity, hypertension, and liver abnormalities, such as steatosis, steatohepatitis, biliary involvement, liver cirrhosis, and nodular regenerative hyperplasia, are commonly observed in patients with TS. The SHOX gene plays a crucial role in short stature and abnormal skeletal phenotype in patients with TS. Abnormal structure formation of the ureter and kidney is also common in patients with TS, and a non-mosaic 45,X karyotype is significantly associated with horseshoe kidneys. TS also affects brain structure and function. In this review, we explore various phenotypic and disease manifestations of TS in different organs, including the reproductive system, cardiovascular system, liver, kidneys, brain, and skeletal system.

Obsessive-compulsive symptoms in two patients with chromosomal disorders involving the X chromosome

INTRODUCTION

The etio-pathophysiology of obsessive-compulsive disorder (OCD) can be explained using a biopsychosocial model. Little is known about obsessive-compulsive symptoms (OCS) in the context of chromosomal disorders involving the X chromosome.

METHODS

Case studies of two patients with chromosomal disorders involving the X chromosome (Patient 1 with a variant of Turner syndrome and Patient 2 with triple X syndrome).

RESULTS

Both patients were treated due to severe OCS. In the research MRI analysis, the most pronounced MRI change in both patients was a gray matter volume loss in the orbitofrontal cortex. Patient 1 additionally showed left mesiotemporal changes. Patient 2 presented with global gray matter volume reduction, slowing in EEG, and a reduced intelligence quotient.

DISCUSSION

OCS could occur in the context of Turner syndrome or triple X syndrome. The detected MRI changes would be compatible with dysfunction of the cortico-striato-thalamo-cortical loops involved in OCD pathophysiology. Further studies with larger patient groups should investigate whether this association can be validated.

Altered Brain Structure in Infants with Turner Syndrome

Turner syndrome (TS) is a genetic disorder affecting approximately 1:2000 live-born females. It results from partial or complete X monosomy and is associated with a range of clinical issues including a unique cognitive profile and increased risk for certain behavioral problems. Structural neuroimaging studies in adolescents, adults, and older children with TS have revealed altered neuroanatomy but are unable to identify when in development differences arise. In addition, older children and adults have often been exposed to years of growth hormone and/or exogenous estrogen therapy with potential implications for neurodevelopment. The study presented here is the first to test whether brain structure is altered in infants with TS. Twenty-six infants with TS received high-resolution structural MRI scans of the brain at 1 year of age and were compared to 47 typically developing female and 39 typically developing male infants. Results indicate that the typical neuroanatomical profile seen in older individuals with TS, characterized by decreased gray matter volumes in premotor, somatosensory, and parietal-occipital cortex, is already present at 1 year of age, suggesting a stable phenotype with origins in the prenatal or early postnatal period.

Effects of X Chromosome Monosomy and Genomic Imprinting on Observational Markers of Social Anxiety in Prepubertal Girls with Turner Syndrome

Previous studies have suggested that girls with Turner syndrome (TS) exhibit symptoms of social anxiety during interactions with others. However, few studies have quantified these behaviors during naturalistic face-to-face social encounters. In this study, we coded observational markers of social anxiety in prepubertal girls with TS and age-matched controls during a 10-min social encounter with an unfamiliar examiner. Results showed that girls with TS exhibited significantly higher levels of gaze avoidance compared to controls. Impairments in social gaze were particularly increased in girls with a maternally retained X chromosome (Xm), suggesting a genomic imprinting effect. These data indicate that social gaze avoidance may be a critical behavioral marker for identifying early social dysfunction in young girls with TS.

Brain Development in School-Age and Adolescent Girls: Effects of Turner Syndrome, Estrogen Therapy, and Genomic Imprinting

BACKGROUND

The study of Turner syndrome (TS) offers a unique window of opportunity for advancing scientific knowledge of how X chromosome gene imprinting, epigenetic factors, hormonal milieu, and chronologic age affect brain development in females.

METHODS

We described brain growth trajectories in 55 girls with TS and 53 typically developing girls (258 magnetic resonance imaging datasets) spanning 5 years. Using novel nonparametric and mixed effects analytic approaches, we evaluated influences of X chromosome genomic imprinting and hormone replacement therapy on brain development.

RESULTS

Parieto-occipital gray and white matter regions showed slower growth during typical pubertal timing in girls with TS relative to typically developing girls. In contrast, some basal ganglia, cerebellar, and limited cortical areas showed enhanced volume growth with peaks around 10 years of age.

CONCLUSIONS

The parieto-occipital finding suggests that girls with TS may be particularly vulnerable to altered brain development during adolescence. Basal ganglia regions may be relatively preserved in TS owing to their maturational growth before or early in typical pubertal years. Taken together, our findings indicate that particular brain regions are more vulnerable to TS genetic and hormonal effects during puberty. These specific alterations in neurodevelopment may be more likely to affect long-term cognitive behavioral outcomes in young girls with this common genetic condition.

Neurobiological mechanisms underlying sex-related differences in stress-related disorders: Effects of neuroactive steroids on the hippocampus

Men and women differ in their vulnerability to a variety of stress-related illnesses, but the underlying neurobiological mechanisms are not well understood. This is likely due to a comparative dearth of neurobiological studies that assess male and female rodents at the same time, while human neuroimaging studies often don't model sex as a variable of interest. These sex differences are often attributed to the actions of sex hormones, i.e. estrogens, progestogens and androgens. In this review, we summarize the results on sex hormone actions in the hippocampus and seek to bridge the gap between animal models and findings in humans. However, while effects of sex hormones on the hippocampus are largely consistent in animals and humans, methodological differences challenge the comparability of animal and human studies on stress effects. We summarise our current understanding of the neurobiological mechanisms that underlie sex-related differences in behavior and discuss implications for stress-related illnesses.

Polygenic risk for circulating reproductive hormone levels and their influence on hippocampal volume and depression susceptibility

Altered reproductive hormone levels have been associated with the pathophysiology of depressive disorders and this risk may be imparted by their modulatory effect upon hippocampal structure and function. Currently it is unclear whether altered levels of reproductive hormones are causally associated with hippocampal volume reductions and the risk of depressive disorders. Here, we utilize genome-wide association study (GWAS) summary statistics from a GWAS focusing on reproductive hormones, consisting of 2913 individuals. Using this data, we generated polygenic risk scores (PRS) for estradiol, progesterone, prolactin and testosterone in the European RADIANT cohort consisting of 176 postpartum depression (PPD) cases (100% female, mean age: 41.6 years old), 2772 major depressive disorder (MDD) cases (68.6% female, mean age: 46.9 years old) and 1588 control participants (62.5% female, mean age: 42.4 years old), for which there was also a neuroimaging subset of 111 individuals (60.4% female, mean age: 50.0 years old). Only the best-fit PRS for estradiol showed a significant negative association with hippocampal volume, as well as many of its individual subfields; including the molecular layer and granule cell layer of the dentate gyrus, subiculum, CA1, CA2/3 and CA4 regions. Interestingly, several of these subfields are implicated in adult hippocampal neurogenesis. When we tested the same estradiol PRS for association with case-control status for PPD or MDD there was no significant relationship observed. Here, we provide evidence that genetic risk for higher plasma estradiol is negatively associated with hippocampal volume, but this does not translate into an increased risk of MDD or PPD. This work suggests that the relationship between reproductive hormones, the hippocampus, and depression is complex, and that there may not be a clear-cut pathway for etiology or risk moderation.

Carriage of Supernumerary Sex Chromosomes Decreases the Volume and Alters the Shape of Limbic Structures

Sex chromosome aneuploidy (SCA) increases risk for several psychiatric disorders associated with the limbic system, including mood and autism spectrum disorders. Thus, SCA offers a genetics-first model for understanding the biological basis of psychopathology. Additionally, the sex-biased prevalence of many psychiatric disorders could potentially reflect sex chromosome dosage effects on brain development. To clarify how limbic anatomy varies across sex and sex chromosome complement, we characterized amygdala and hippocampus structure in a uniquely large sample of patients carrying supernumerary sex chromosomes (n = 132) and typically developing controls (n = 166). After adjustment for sex-differences in brain size, karyotypically normal males (XY) and females (XX) did not differ in volume or shape of either structure. In contrast, all SCAs were associated with lowered amygdala volume relative to gonadally-matched controls. This effect was robust to three different methods for total brain volume adjustment, including an allometric analysis that derived normative scaling rules for these structures in a separate, typically developing population (n = 79). Hippocampal volume was insensitive to SCA after adjustment for total brain volume. However, surface-based analysis revealed that SCA, regardless of specific karyotype, was consistently associated with a spatially specific pattern of shape change in both amygdala and hippocampus. In particular, SCA was accompanied by contraction around the basomedial nucleus of the amygdala and an area crossing the hippocampal tail. These results demonstrate the power of SCA as a model to understand how copy number variation can precipitate changes in brain systems relevant to psychiatric disease.

Gender-Specific Degeneration of Dementia-Related Subcortical Structures Throughout the Lifespan

Age-related changes in brain structure are a question of interest to a broad field of research. Structural decline has been consistently, but not unambiguously, linked to functional consequences, including cognitive impairment and dementia. One of the areas considered of crucial importance throughout this process is the medial temporal lobe, and primarily the hippocampal region. Gender also has a considerable effect on volume deterioration of subcortical grey matter (GM) structures, such as the hippocampus. The influence of age×gender interaction on disproportionate GM volume changes might be mediated by hormonal effects on the brain. Hippocampal volume loss appears to become accelerated in the postmenopausal period. This decline might have significant influences on neuroplasticity in the CA1 region of the hippocampus highly vulnerable to pathological influences. Additionally, menopause has been associated with critical pathobiochemical changes involved in neurodegeneration. The micro- and macrostructural alterations and consequent functional deterioration of critical hippocampal regions might result in clinical cognitive impairment-especially if there already is a decline in the cognitive reserve capacity. Several lines of potential vulnerability factors appear to interact in the menopausal period eventually leading to cognitive decline, mild cognitive impairment, or Alzheimer's disease. This focused review aims to delineate the influence of unmodifiable risk factors of neurodegenerative processes, i.e., age and gender, on critical subcortical GM structures in the light of brain derived estrogen effects. The menopausal period appears to be of key importance for the risk of cognitive decline representing a time of special vulnerability for molecular, structural, and functional influences and offering only a narrow window for potential protective effects.

Sexual dimorphism of frailty and cognitive impairment: Potential underlying mechanisms (Review)

The aim of the present study was to assess systematically gender differences in susceptibility to frailty and cognitive performance decline, and the underlying mechanisms. A systematic assessment was performed of the identified reviews of cohort, mechanistic and epidemiological studies. The selection criteria of the present study included: i) Sexual dimorphism of frailty, ii) sexual dimorphism of subjective memory decline (impairment) and atrophy of hippocampus during early life, iii) sexual dimorphism of late‑onset Alzheimer's disease and iv) sexual dimorphism mechanisms underlying frailty and cognitive impairment. Males exhibit a susceptibility to poor memory performance and a severe atrophy of the hippocampus during early life and females demonstrate a higher prevalence for frailty and late‑life dementia. The different alterations within the hypothalamic‑pituitary‑gonadal/adrenal axis, particularly with regard to gonadal hormones, cortisol and dehydroepiandrosterone/sulfate‑bound dehydroepiandrosterone prior to and following andropause in males and menopause in females, serve important roles in sexual dimorphism of frailty and cognitive impairment. These endocrine changes may accelerate immunosenescence, weaken neuroprotective and neurotrophic effects, and promote muscle catabolism. The present study suggested that these age‑associated endocrine alterations interact with gender‑specific genetic and epigenetic factors, together with immunosenescence and iron accumulation. Environment factors, including psychological factors, are additional potential causes of the sexual dimorphism of frailty and cognitive impairment.

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.

In-vivo Dynamics of the Human Hippocampus across the Menstrual Cycle

Sex hormones fluctuate during the menstrual cycle. Evidence from animal studies suggests similar subtle fluctuations in hippocampal structure, predominantly linked to estrogen. Hippocampal abnormalities have been observed in several neuropsychiatric pathologies with prominent sexual dimorphism. Yet, the potential impact of subtle sex-hormonal fluctuations on human hippocampal structure in health is unclear. We tested the feasibility of longitudinal neuroimaging in conjunction with rigorous menstrual cycle monitoring to evaluate potential changes in hippocampal microstructure associated with physiological sex-hormonal changes. Thirty longitudinal diffusion weighted imaging scans of a single healthy female subject were acquired across two full menstrual cycles. We calculated hippocampal fractional anisotropy (FA), a measure sensitive to changes in microstructural integrity, and investigated potential correlations with estrogen. We observed a significant positive correlation between FA values and estrogen in the hippocampus bilaterally, revealing a peak in FA closely paralleling ovulation. This exploratory, single-subject study demonstrates the feasibility of a longitudinal DWI scanning protocol across the menstrual cycle and is the first to link subtle endogenous hormonal fluctuations to changes in FA in vivo. In light of recent attempts to neurally phenotype single humans, our findings highlight menstrual cycle monitoring in parallel with highly sampled individual neuroimaging data to address fundamental questions about the dynamics of plasticity in the adult brain.

Face perception in women with Turner syndrome and its underlying factors

Turner syndrome (TS) is a chromosomal condition that affects development in females. It is characterized by short stature, ovarian failure and other congenital malformations, due to a partial or complete absence of the sex chromosome. Women with TS frequently suffer from various physical and hormonal dysfunctions, along with impairments in visual-spatial processing and social cognition difficulties. Previous research has also shown difficulties in face and emotion perception. In the current study we examined two questions: First, whether women with TS, that are impaired in face perception, also suffer from deficits in face-specific processes. The second question was whether these face impairments in TS are related to visual-spatial perceptual dysfunctions exhibited by TS individuals, or to impaired social cognition skills. Twenty-six women with TS and 26 control participants were tested on various cognitive and psychological tests to assess visual-spatial perception, face and facial expression perception, and social cognition skills. Results show that women with TS were less accurate in face perception and facial expression processing, yet they exhibited normal face-specific processes (configural and holistic processing). They also showed difficulties in spatial perception and social cognition capacities. Additional analyses revealed that their face perception impairments were related to their deficits in visual-spatial processing. Thus, our results do not support the claim that the impairments in face processing observed in TS are related to difficulties in social cognition. Rather, our data point to the possibility that face perception difficulties in TS stem from visual-spatial impairments and may not be specific to faces.

Sex differences in amygdala shape: Insights from Turner syndrome

OBJECTIVE

Sex differences in the manifestation of psychiatric disorders, including anxiety disorders, are among the most prominent findings in psychiatry. The study of Turner syndrome (TS), caused by X-monosomy, has the potential to reveal mechanisms that underline male/female differences in neuropsychiatric disorders. The amygdala has been implicated in numerous neuropsychiatric disorders. Previous studies suggest an effect of TS on amygdala volume as well as on amygdala-related behaviors such as anxiety. Our objective is to investigate the amygdala shape in TS. Specifically, we tested whether amygdala enlargements in TS are localized to specific nuclei implicated in anxiety, such as the basomedial nucleus.

EXPERIMENTAL DESIGN

We use a surface-based analytical modeling approach to contrast 41 pre-estrogen treatment girls with TS (mean age 8.6 ± 2.4) with 34 age-and sex-matched typically developing (TD) controls (mean age 8.0 ± 2.8). Anxiety symptoms were assessed using the Revised Children's Manifest Anxiety Scale - 2 (RCMAS-2) in both groups.

PRINCIPAL OBSERVATIONS

TS was associated with anomalous enlargement of the amygdala. Surface-based modeling revealed shape differences (increased radial-distances) in bilateral basal and basomedial nuclei within the basolateral complex. RCMAS-2 Total Anxiety t-score was significantly higher in participants with TS compared with TD controls (P = 0.012).

CONCLUSIONS

Group differences in global amygdala volumes were driven by local morphological increases in areas that are critically involved in face emotion processing and anxiety. In the context of increased amygdala volumes in TS, our results also showed increased worry and social anxiety in young girls with TS compared with TD.

Morphological Changes of Amygdala in Turner Syndrome Patients

AIMS

Turner's syndrome (TS) losts one of the X chromosomes and exhibits social cognition deficits. Previous studies have reported that women with TS demonstrated structural and functional abnormalities in brain, including increased volume in amygdala. However, most studies regarded the amygdala as a whole, and the abnormalities in the specific subregions of amygdala in TS have not been studied. Here, we aimed to investigate the local morphological changes of amygdala in TS using the surface morphology analysis method.

METHODS

A total of 19 adolescents with 45XO TS and 20 matched adolescents with typical development were evaluated using magnetic resonance imaging. The amygdalae of all participants were manually delineated. 3D surface remodeling and parameterization were performed based on the outlined boundaries of amygdalae. We extracted two surface metrics, namely direct Euclidean displacement and normal projection that were used to represent the morphology of amygdala.

RESULTS

Statistical analysis showed significant outward deformation in the laterobasal subregion of left amygdala in patients with TS, compared with the controls using either direct Euclidean displacement or normal displacement.

CONCLUSIONS

Our findings provide novel insight into the pathological changes in the amygdala of patients with TS.

Alexithymia, emotion perception, and social assertiveness in adult women with Noonan and Turner syndromes

Noonan syndrome (NS) and Turner syndrome (TS) are associated with cognitive problems and difficulties in affective information processing. While both phenotypes include short stature, facial dysmorphisms, and a webbed neck, genetic etiology and neuropsychological phenotype differ significantly. The present study examines putative differences in affective information processing and social assertiveness between adult women with NS and TS. Twenty-six women with NS, 40 women with TS, and 40 female controls were matched on age and intelligence, and subsequently compared on (1) alexithymia, measured by the Bermond-Vorst Alexithymia Questionnaire, (2) emotion perception, evaluated by the Emotion Recognition Task, and (3) social assertiveness and social discomfort, assessed by the Scale for Interpersonal Behavior. Women with TS showed higher levels of alexithymia than women with NS and controls (P-values < 0.001), whereas women with NS had more trouble recognizing angry facial expressions in comparison with controls (P = 0.01). No significant group differences were found for the frequency of social assertiveness and the level of social discomfort. Women with NS and TS demonstrated different patterns of impairment in affective information processing, in terms of alexithymia and emotion perception. The present findings suggest neuropsychological phenotyping to be helpful for the diagnosis of specific cognitive-affective deficits in genetic syndromes, for the enhancement of genetic counseling, and for the development of personalized treatment plans.

Assessing gonadal hormone contributions to affective psychopathologies across humans and animal models

Despite increasing acknowledgement of hormonal contributions to mood and anxiety disorders, the underlying mechanisms by which gonadal hormones influence psychopathology-related behaviours remain unknown. This review focuses on recent research that examines the influence of gonadal steroid hormones, including androgens, oestrogens, and progesterone, on mood and anxiety-related behaviours in human health and disease. To this aim, the literature was surveyed for studies that assess conditions with suspected underlying hormonal imbalances in otherwise healthy participants (e.g., premenstrual dysphoric disorder, postmenopausal depression) as well as conditions linked to congenital endocrine abnormalities (e.g., Turner Syndrome, Klinefelter Syndrome, polycystic ovary syndrome, congenital adrenal hyperplasia, familial male precocious puberty, androgen insensitivity syndrome). Furthermore, to better inform clinical work and to create a translational bridge, a second goal was to set human psychopathologies and animal models of these conditions side-by-side. In the second part of the review, based on consistencies revealed in the existing literature across conditions, a new model for the impact of gonadal hormones on anxious and depressed behavioural states is proposed. Finally, we conclude by proposing directions for future research, including the development of specific tasks suitable for cross-species comparisons to increase our knowledge of the role of gonadal hormones in mood and anxiety.

Sex differences in cognitive impairment and Alzheimer's disease

Studies have shown differences in specific cognitive ability domains and risk of Alzheimer's disease between the men and women at later age. However it is important to know that sex differences in cognitive function during adulthood may have their basis in both organizational effects, i.e., occurring as early as during the neuronal development period, as well as in activational effects, where the influence of the sex steroids influence brain function in adulthood. Further, the rate of cognitive decline with aging is also different between the sexes. Understanding the biology of sex differences in cognitive function will not only provide insight into Alzheimer's disease prevention, but also is integral to the development of personalized, gender-specific medicine. This review draws on epidemiological, translational, clinical, and basic science studies to assess the impact of sex differences in cognitive function from young to old, and examines the effects of sex hormone treatments on Alzheimer's disease in men and women.

Typical and atypical brain development: a review of neuroimaging studies

In the course of development, the brain undergoes a remarkable process of restructuring as it adapts to the environment and becomes more efficient in processing information. A variety of brain imaging methods can be used to probe how anatomy, connectivity, and function change in the developing brain. Here we review recent discoveries regarding these brain changes in both typically developing individuals and individuals with neurodevelopmental disorders. We begin with typical development, summarizing research on changes in regional brain volume and tissue density, cortical thickness, white matter integrity, and functional connectivity. Space limits preclude the coverage of all neurodevelopmental disorders; instead, we cover a representative selection of studies examining neural correlates of autism, attention deficit/hyperactivity disorder, Fragile X, 22q11.2 deletion syndrome, Williams syndrome, Down syndrome, and Turner syndrome. Where possible, we focus on studies that identify an age by diagnosis interaction, suggesting an altered developmental trajectory. The studies we review generally cover the developmental period from infancy to early adulthood. Great progress has been made over the last 20 years in mapping how the brain matures with MR technology. With ever-improving technology, we expect this progress to accelerate, offering a deeper understanding of brain development, and more effective interventions for neurodevelopmental disorders.

Brain sex matters: estrogen in cognition and Alzheimer's disease

Estrogens are the primary female sex hormones and play important roles in both reproductive and non-reproductive systems. Estrogens can be synthesized in non-reproductive tissues such as liver, heart, muscle, bone and the brain. During the past decade, increasing evidence suggests that brain estrogen can not only be synthesized by neurons, but also by astrocytes. Brain estrogen also works locally at the site of synthesis in paracrine and/or intracrine fashion to maintain important tissue-specific functions. Here, we will focus on the biology of brain estrogen and its impact on cognitive function and Alzheimer's disease. This comprehensive review provides new insights into brain estrogens by presenting a better understanding of the tissue-specific estrogen effects and their roles in healthy ageing and cognitive function.

Influence of the X-chromosome on neuroanatomy: evidence from Turner and Klinefelter syndromes

Studies of sex effects on neurodevelopment have traditionally focused on animal models investigating hormonal influences on brain anatomy. However, more recent evidence suggests that sex chromosomes may also have direct upstream effects that act independently of hormones. Sex chromosome aneuploidies provide ideal models to examine this framework in humans, including Turner syndrome (TS), where females are missing one X-chromosome (45X), and Klinefelter syndrome (KS), where males have an additional X-chromosome (47XXY). As these disorders essentially represent copy number variants of the sex chromosomes, investigation of brain structure across these disorders allows us to determine whether sex chromosome gene dosage effects exist. We used voxel-based morphometry to investigate this hypothesis in a large sample of children in early puberty, to compare regional gray matter volumes among individuals with one (45X), two (typically developing 46XX females and 46XY males), and three (47XXY) sex chromosomes. Between-group contrasts of TS and KS groups relative to respective sex-matched controls demonstrated highly convergent patterns of volumetric differences with the presence of an additional sex chromosome being associated with relatively decreased parieto-occipital gray matter volume and relatively increased temporo-insular gray matter volumes. Furthermore, z-score map comparisons between TS and KS cohorts also suggested that this effect occurs in a linear dose-dependent fashion. We infer that sex chromosome gene expression directly influences brain structure in children during early stages of puberty, extending our understanding of genotype-phenotype mechanisms underlying sex differences in the brain.

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.

Neuroanatomical correlates of Klinefelter syndrome studied in relation to the neuropsychological profile

Brain imaging in Klinefelter syndrome (47, XXY) (KS), a genetic disorder characterized by the presence of an extra X chromosome, may contribute to understanding the relationship between gene expression, brain structure, and subsequent cognitive disabilities and psychiatric disorders. We conducted the largest to date voxel-based morphometry study of 65 KS subjects and 65 controls matched for age and education and correlated these data to neuropsychological test scores. The KS patients had significantly smaller total brain volume (TBV), total gray matter volume (GMV) and total white matter volume (WMV) compared to controls, whereas no volumetric difference in cerebral spinal fluid (CSF) was found. There were no differences in TBV, GMV, WMV or CSF between testosterone treated KS (T-KS) and untreated KS (U-KS) patients. Compared to controls, KS patients had significantly decreased GMV bilaterally in insula, putamen, caudate, hippocampus, amygdala, temporal pole and frontal inferior orbita. Additionally, the right parahippocampal region and cerebellar volumes were reduced in KS patients. KS patients had significantly larger volumes in right postcentral gyrus, precuneus and parietal regions. Multivariate classification analysis discriminated KS patients from controls with 96.9% (p < 0.001) accuracy. Regression analyses, however, revealed no significant association between GMV differences and cognitive and psychological factors within the KS patients and controls or the groups combined. These results show that although gene dosage effect of having and extra X-chromosome may lead to large scale alterations of brain morphometry and extended cognitive disabilities no simple correspondence links these measures.

Sex differences in cortical thickness and their possible genetic and sex hormonal underpinnings

Although it has been shown that cortical thickness (Cth) differs between sexes, the underlying mechanisms are unknown. Seeing as XXY males have 1 extra X chromosome, we investigated the possible effects of X- and sex-chromosome dosage on Cth by comparing data from 31 XXY males with 39 XY and 47 XX controls. Plasma testosterone and estrogen were also measured in an effort to differentiate between possible sex-hormone and sex-chromosome gene effects. Cth was calculated with FreeSurfer software. Parietal and occipital Cth was greater in XX females than XY males. In these regions Cth was inversely correlated with z-normalized testosterone. In the motor strip, the cortex was thinner in XY males compared with both XX females and XXY males, indicating the possibility of an X-chromosome gene-dosage effect. XXY males had thinner right superior temporal and left middle temporal cortex, and a thicker right orbitofrontal cortex and lingual cortex than both control groups. Based on these data and previous reports from women with XO monosomy, it is hypothesized that programming of the motor cortex is influenced by processes linked to X-escapee genes, which do not have Y-chromosome homologs, and that programming of the superior temporal cortex is mediated by X-chromosome escapee genes with Y-homologs.

Genomic imprinting effects of the X chromosome on brain morphology

There is increasing evidence that genomic imprinting, a process by which certain genes are expressed in a parent-of-origin-specific manner, can influence neurogenetic and psychiatric manifestations. While some data suggest possible imprinting effects of the X chromosome on physical and cognitive characteristics in humans, there is no compelling evidence that X-linked imprinting affects brain morphology. To address this issue, we investigated regional cortical volume, thickness, and surface area in 27 healthy controls and 40 prepubescent girls with Turner syndrome (TS), a condition caused by the absence of one X chromosome. Of the young girls with TS, 23 inherited their X chromosome from their mother (X(m)) and 17 from their father (X(p)). Our results confirm the existence of significant differences in brain morphology between girls with TS and controls, and reveal the presence of a putative imprinting effect among the TS groups: girls with X(p) demonstrated thicker cortex than those with X(m) in the temporal regions bilaterally, while X(m) individuals showed bilateral enlargement of gray matter volume in the superior frontal regions compared with X(p). These data suggest the existence of imprinting effects of the X chromosome that influence both cortical thickness and volume during early brain development, and help to explain variability in cognitive and behavioral manifestations of TS with regard to the parental origin of the X chromosome.

Magnetic resonance imaging in paediatric psychoneuroendocrinology: a new frontier for understanding the impact of hormones on emotion and cognition

Mounting magnetic resonance imaging (MRI) research is characterising the neurobiological trajectories of healthy human brain development. In parallel, studies increasingly acknowledge the relevance of perturbations of these trajectories for adolescent and adult psychopathology. Although an influence of steroid hormones on mood and anxiety disorders has been demonstrated in adults, very little is known about how steroid hormones alter human brain development and contribute to adolescent psychopathology. This review focuses on recent evidence obtained from structural and functional MRI in children and adolescents with genetic endocrine disorders and with characteristic fluctuations in androgen or oestrogen levels (familial male precocious puberty, congenital adrenal hyperplasia, Klinefelter syndrome and Turner syndrome). It aims to highlight how neurobiological findings from these paediatric endocrine disorders can provide insight into the contribution of sex steroids with respect to the development of neurocircuitry involved in affective processing (amygdala, hippocampus) and cognitive control (prefrontal cortex, inferior frontal gyrus, striatum). In addition, findings from these populations may also provide important information on aberrant psychological processes relevant for the clinical care and management of these populations. Finally, the findings are discussed within the context of current frameworks in animal models, such as the organisational-activational hypothesis or the aromatisation hypothesis. The review ends with a discussion of open questions for future enquiry with the goal of integrating translational models with current knowledge of endocrine disorders and developmental studies in healthy populations.

X-inactivation, imprinting, and long noncoding RNAs in health and disease

X chromosome inactivation and genomic imprinting are classic epigenetic processes that cause disease when not appropriately regulated in mammals. Whereas X chromosome inactivation evolved to solve the problem of gene dosage, the purpose of genomic imprinting remains controversial. Nevertheless, the two phenomena are united by allelic control of large gene clusters, such that only one copy of a gene is expressed in every cell. Allelic regulation poses significant challenges because it requires coordinated long-range control in cis and stable propagation over time. Long noncoding RNAs have emerged as a common theme, and their contributions to diseases of imprinting and the X chromosome have become apparent. Here, we review recent advances in basic biology, the connections to disease, and preview potential therapeutic strategies for future development.

Reduced hippocampal volume and verbal memory performance associated with interleukin-6 and tumor necrosis factor-alpha levels in chemotherapy-treated breast cancer survivors

Many survivors of breast cancer show significant cognitive impairments, including memory deficits. Inflammation induced by chemotherapy may contribute to hippocampal changes that underlie these deficits. In this cross-sectional study, we measured bilateral hippocampal volumes from high-resolution magnetic resonance images in 42 chemotherapy-treated breast cancer survivors and 35 healthy female controls. Patients with breast cancer were, on average, 4.8 ± 3.4 years off-therapy. In a subset of these participants (20 breast cancer, 23 controls), we quantified serum cytokine levels. Left hippocampal volumes and memory performance were significantly reduced and interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNFα) concentrations were significantly elevated in the breast cancer group compared to controls. In the breast cancer group, lower left hippocampal volume was associated with higher levels of TNFα and lower levels of IL-6 with a significant interaction between these two cytokines suggesting a potential modulatory effect of IL-6 on TNFα. Verbal memory performance was associated with cytokine levels and left hippocampal volume in both groups. These findings provide evidence of altered hippocampal volume and verbal memory difficulties following breast cancer chemotherapy that may be mediated by TNFα and IL-6.

Update on Turner and Noonan syndromes

Turner syndrome (TS) and Noonan syndrome (NS) have short stature as a constant feature; however, both conditions can present clinicians with a challenging array of genetic, cardiovascular, developmental, and psychosocial issues. In recent years, important advances have been achieved in each of these areas. This article reviews these two syndromes and provides updates on recent developments in diagnostic evaluation, growth and development, psychological issues, and treatment options for patients with TS and NS.

Sex differences in the human brain and the impact of sex chromosomes and sex hormones

While there has been increasing support for the existence of cerebral sex differences, the mechanisms underlying these differences are unclear. Based on animal data, it has long been believed that sexual differentiation of the brain is primarily linked to organizational effects of fetal testosterone. This view is, however, in question as more recent data show the presence of sex differences before the onset of testosterone production. The present study focuses on the impact that sex chromosomes might have on these differences. Utilizing the inherent differences in sex and X-chromosome dosage among XXY males, XY males, and XX females, comparative voxel-based morphometry was conducted using sex hormones and sex chromosomes as covariates. Sex differences in the cerebellar and precentral gray matter volumes (GMV) were found to be related to X-chromosome dosage, whereas sex differences in the amygdala, the parahippocamus, and the occipital cortex were linked to testosterone levels. An increased number of sex chromosomes was associated with reduced GMV in the amygdala, caudate, and the temporal and insular cortices, with increased parietal GMV and reduced frontotemporal white matter volume. No selective, testosterone independent, effect of the Y-chromosome was detected. Based on these observations, it was hypothesized that programming of the motor cortex and parts of cerebellum is mediated by processes linked to X-escapee genes, which do not have Y-chromosome homologs, and that programming of certain limbic structures involves testosterone and X-chromosome escapee genes with Y-homologs.

Cortical brain morphology in young, estrogen-naive, and adolescent, estrogen-treated girls with Turner syndrome

Turner syndrome (TS) is a genetic condition that permits direct investigation of the complex interaction among genes, hormones, behavior, and brain development. Here, we used automated segmentation and surface-based morphometry to characterize the differences in brain morphology in children (n = 30) and adolescents (n = 16) with TS relative to age- and sex-matched control groups (n = 21 and 24, respectively). Our results show that individuals with TS, young and adolescent, present widespread reduction of gray matter volume, white matter volume and surface area (SA) over both parietal and occipital cortices bilaterally, as well as enlarged amygdala. In contrast to the young cohort, adolescents with TS showed significantly larger mean cortical thickness and significantly smaller total SA compared with healthy controls. Exploratory developmental analyses suggested aberrant regional brain maturation in the parahippocampal gyrus and orbitofrontal regions from childhood to adolescence in TS. These findings show the existence of abnormal brain morphology early in development in TS, but also suggest the presence of altered neurodevelopmental trajectories in some regions, which could potentially be the consequences of estrogen deficiency, both pre- and postnatally.

Turner syndrome: advances in understanding altered cognition, brain structure and function

PURPOSE OF REVIEW

Turner syndrome, which results from the complete or partial loss of a sex chromosome, is associated with a particular pattern of cognitive impairments and strengths and an increased risk for specific neurodevelopmental disorders. This review highlights recent progress in understanding brain structure and function in Turner syndrome and identifies several critical research needs.

RECENT FINDINGS

Recent work on social cognition in Turner syndrome has identified a range of difficulties despite a maintained social appetite, a disconnect which could result in distress for affected individuals. Progress has been made in identifying foundational deficits in attention and executive function that could explain visual-spatial and arithmetical impairments. Neuroimaging studies have advanced our understanding of brain development and function through the application of cutting edge analysis techniques. Haploinsufficiency of genes, failure to express parentally imprinted genes, uncovering of X chromosome mutations, and gonadal steroid deficiency may all contribute to altered brain development, but additional work is required to link specific mechanisms to specific phenotypes. Also needed are studies of interventions to assist individuals with Turner syndrome in visual-spatial, mathematical, and social skills.

SUMMARY

Ultimately a better understanding of brain structure and function in Turner syndrome will generate new therapeutic approaches for this population.

Parental origin of the X-chromosome does not influence growth hormone treatment effect in Turner syndrome

CONTEXT

The parental origin of the intact X-chromosome has been reported to affect phenotype and response to GH treatment in Turner syndrome (TS).

OBJECTIVE

Our objective was to evaluate the influence of the parental origin of the X-chromosome on body growth and GH treatment effect in TS.

DESIGN AND SETTING

We conducted a population-based cohort study of TS patients previously treated with GH.

PARTICIPANTS

Participants included patients with a nonmosaic 45,X karyotype; 556 women were identified as eligible, 233 (49%) of whom participated, together with their mothers. Data were analyzed for 180 of these patients.

MAIN OUTCOME MEASURES

We performed fluorescence in situ hybridization analysis to exclude mosaicism and microsatellite analysis of nine polymorphic markers in DNA from the patients and their mothers. The influence on growth and effect of GH were analyzed by univariate and multivariate methods.

RESULTS

The X-chromosome was of paternal origin (X(pat)) in 52 (29%) of 180 and of maternal origin (X(mat)) in 128 (71%) of 180 patients. Height gain from the start of GH treatment to adult height was similar in X(mat) and X(pat) patients (+2.1 ± 0.9 vs. +2.2 ± 0.8 TS sd score, P = 0.45). The lack of influence of parental origin of the X-chromosome was confirmed in multivariate analysis. Parental origin of the X-chromosome also had no effect on the other growth characteristics studied, including growth velocity during the first year on GH treatment. Patient height was correlated with the heights of both parents and was not influenced by the parental origin of the X-chromosome.

CONCLUSION

In this, the largest such study carried out to date, the parental origin of the X-chromosome did not alter the effect of GH treatment or affect any other features of growth in TS.

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.

A review on sex differences in processing emotional signals

Interest in sex-related differences in psychological functioning has again come to the foreground with new findings about their possible functional basis in the brain. Sex differences may be one way how evolution has capitalized on the capacity of homologous brain regions to process social information between men and women differently. This paper focuses specifically on the effects of emotional valence, sex of the observed and sex of the observer on regional brain activations. We also discuss the effects of and interactions between environment, hormones, genes and structural differences of the brain in the context of differential brain activity patterns between men and women following exposure to seen expressions of emotion and in this context we outline a number of methodological considerations for future research. Importantly, results show that although women are better at recognizing emotions and express themselves more easily, men show greater responses to threatening cues (dominant, violent or aggressive) and this may reflect different behavioral response tendencies between men and women as well as evolutionary effects. We conclude that sex differences must not be ignored in affective research and more specifically in affective neuroscience.

White matter aberrations in prepubertal estrogen-naive girls with monosomic Turner syndrome

Turner syndrome (TS) offers a unique opportunity to investigate associations among genes, the brain, and cognitive phenotypes. In this study, we used 3 complementary analyses of diffusion tensor imaging (DTI) data (whole brain, region of interest, and fiber tractography) and a whole brain volumetric imaging technique to investigate white matter (WM) structure in prepubertal, nonmosaic, estrogen-naive girls with TS compared with age and sex matched typically developing controls. The TS group demonstrated significant WM aberrations in brain regions implicated in visuospatial abilities, face processing, and sensorimotor and social abilities compared with controls. Extensive spatial overlap between regions of aberrant WM structure (from DTI) and regions of aberrant WM volume were observed in TS. Our findings indicate that complete absence of an X chromosome in young females (prior to receiving exogenous estrogen) is associated with WM aberrations in specific regions implicated in characteristic cognitive features of TS.

Turner syndrome and sexual differentiation of the brain: implications for understanding male-biased neurodevelopmental disorders

Turner syndrome (TS) is one of the most common sex chromosome abnormalities. Affected individuals often show a unique pattern of cognitive strengths and weaknesses and are at increased risk for a number of other neurodevelopmental conditions, many of which are more common in typical males than typical females (e.g., autism and attention-deficit hyperactivity disorder). This phenotype may reflect gonadal steroid deficiency, haploinsufficiency of X chromosome genes, failure to express parentally imprinted genes, and the uncovering of X chromosome mutations. Understanding the contribution of these different mechanisms to outcome has the potential to improve clinical care for individuals with TS and to better our understanding of the differential vulnerability to and expression of neurodevelopmental disorders in males and females. In this paper, we review what is currently known about cognition and brain development in individuals with TS, discuss underlying mechanisms and their relevance to understanding male-biased neurodevelopmental conditions, and suggest directions for future research.

Psychosocial functioning and social cognitive processing in girls with Turner syndrome

OBJECTIVE

Turner syndrome (TS) is a common genetic disorder caused by partial or complete absence of the second X chromosome in females and is associated with a characteristic neurocognitive profile traditionally described by discrepancy between verbal and performance IQ. Difficulties in social functioning have also been increasingly identified in this population. The purpose of this study was to examine elements of social competence and cognition in a pre-estrogen population of girls with TS.

METHODS

The authors administered psychosocial and neurocognitive measures to examine metrics of social function and intelligence in a group of young girls with TS, pre-estrogen treatment (n = 42) and control peers (n = 32), aged between 3 and 12 years.

RESULTS

Girls with TS demonstrated significantly decreased social competency on all dimensions of the Social Responsiveness Scale, with the exception of the Social Motivation subscale, where ratings were comparable with typically developing peers. Performance on social cognitive tasks was also impaired on NEPSY Memory for Faces and Theory of Mind tasks. Differences were further observed on Behavioral Assessment Scales for Children subscales of Hyperactivity, Atypicality, Attention, Social Skills, Activities of Daily Living, and Functional Communication. Group differences in social cognition or behavior remained significant after adjusting for verbal IQ.

CONCLUSION

This study supports the hypothesis that young girls with TS who have not yet received estrogen treatment demonstrate significantly impaired social cognition. Improved understanding of differences in social competence and cognition can increase awareness and inform clinical approaches to identifying and treating social difficulties in individuals with TS.

Diseases associated with genomic imprinting

Genomic imprinting is the phenomenon where the expression of a locus differs between the maternally and paternally inherited alleles. Typically, this manifests as transcriptional silencing of one of the alleles, although many genes are imprinted in a tissue- or isoform-specific manner. Diseases associated with imprinted genes include various cancers, disorders of growth and metabolism, and disorders in neurodevelopment, cognition, and behavior, including certain major psychiatric disorders. In many cases, the disease phenotypes associated with dysfunction at particular imprinted loci can be understood in terms of the evolutionary processes responsible for the origin of imprinting. Imprinted gene expression represents the outcome of an intragenomic evolutionary conflict, where natural selection favors different expression strategies for maternally and paternally inherited alleles. This conflict is reasonably well understood in the context of the early growth effects of imprinted genes, where paternally inherited alleles are selected to place a greater demand on maternal resources than are maternally inherited alleles. Less well understood are the origins of imprinted gene expression in the brain, and their effects on cognition and behavior. This chapter reviews the genetic diseases that are associated with imprinted genes, framed in terms of the evolutionary pressures acting on gene expression at those loci. We begin by reviewing the phenomenon and evolutionary origins of genomic imprinting. We then discuss diseases that are associated with genetic or epigenetic defects at particular imprinted loci, many of which are associated with abnormalities in growth and/or feeding behaviors that can be understood in terms of the asymmetric pressures of natural selection on maternally and paternally inherited alleles. We next described the evidence for imprinted gene effects on adult cognition and behavior, and the possible role of imprinted genes in the etiology of certain major psychiatric disorders. Finally, we conclude with a discussion of how imprinting, and the evolutionary-genetic conflicts that underlie it, may enhance both the frequency and morbidity of certain types of diseases.

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.

Imaging genetics of mood disorders

Mood disorders are highly heritable and have been linked to brain regions of emotion processing. Over the past few years, an enormous amount of imaging genetics studies has demonstrated the impact of risk genes on brain regions and systems of emotion processing in vivo in healthy subjects as well as in mood disorder patients. While sufficient evidence already exists for several monaminergic genes as well as for a few non-monoaminergic genes, such as brain-derived neurotrophic factor (BDNF) in healthy subjects, many others only have been investigated in single studies so far. Apart from these studies, the present review also covers imaging genetics studies applying more complex genetic disease models of mood disorders, such as epistasis and gene-environment interactions, and their impact on brain systems of emotion processing. This review attempts to provide a comprehensive overview of the rapidly growing field of imaging genetics studies in mood disorder research.

Autism-lessons from the X chromosome

Recognized cases of autism spectrum disorders are on the rise. It is unclear whether this increase is attributable to secular trends in biological susceptibility, or to a change in diagnostic practices and recognition. One hint concerning etiological influences is the universally reported male excess (in the range of 4:1 to 10:1). Evidence suggests that genetic influences from the X chromosome play a crucial role in engendering this male vulnerability. In this review, we discuss three categories of genetic disease that highlight the importance of X-linked genes in the manifestation of an autistic phenotype: aneuploides (Turner syndrome and Klinefelter syndrome), trinucleotide expansions (Fragile X syndrome) and nucleotide mutations (Rett Syndrome, Neuroligins 3 & 4, and SLC6A8). The lessons from these diseases include an understanding of autistic features as a broad phenotype rather than as a single clinical entity, the role of multiple genes either alone or in concert with the manifestation of autistic features, and the role of epigenetic factors such as imprinting and X-inactivation in the expression of disease severity. Better understanding of the clinical phenotypes of social cognition and the molecular neurogenetics of X-linked gene disorders will certainly provide additional tools for understanding autism in the years to come.

ATRX partners with cohesin and MeCP2 and contributes to developmental silencing of imprinted genes in the brain

Human developmental disorders caused by chromatin dysfunction often display overlapping clinical manifestations, such as cognitive deficits, but the underlying molecular links are poorly defined. Here, we show that ATRX, MeCP2, and cohesin, chromatin regulators implicated in ATR-X, RTT, and CdLS syndromes, respectively, interact in the brain and colocalize at the H19 imprinting control region (ICR) with preferential binding on the maternal allele. Importantly, we show that ATRX loss of function alters enrichment of cohesin, CTCF, and histone modifications at the H19 ICR, without affecting DNA methylation on the paternal allele. ATRX also affects cohesin, CTCF, and MeCP2 occupancy within the Gtl2/Dlk1 imprinted domain. Finally, we show that loss of ATRX interferes with the postnatal silencing of the maternal H19 gene along with a larger network of imprinted genes. We propose that ATRX, cohesin, and MeCP2 cooperate to silence a subset of imprinted genes in the postnatal mouse brain.

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.