Mutations in human DNA methyltransferase DNMT1 induce specific genome-wide epigenomic and transcriptomic changes in neurodevelopment.

DNA methyltransferase type 1 (DNMT1) is a major enzyme involved in maintaining the methylation pattern after DNA replication. Mutations in DNMT1 have been associated with autosomal dominant cerebellar ataxia, deafness and narcolepsy (ADCA-DN). We used fibroblasts, induced pluripotent stem cells (iPSCs) and induced neurons (iNs) generated from patients with ADCA-DN and controls, to explore the epigenomic and transcriptomic effects of mutations in DNMT1. We show cell type-specific changes in gene expression and DNA methylation patterns. DNA methylation and gene expression changes were negatively correlated in iPSCs and iNs. In addition, we identified a group of genes associated with clinical phenotypes of ADCA-DN, including PDGFB and PRDM8 for cerebellar ataxia, psychosis and dementia and NR2F1 for deafness and optic atrophy. Furthermore, ZFP57, which is required to maintain gene imprinting through DNA methylation during early development, was hypomethylated in promoters and exhibited upregulated expression in patients with ADCA-DN in both iPSC and iNs. Our results provide insight into the functions of DNMT1 and the molecular changes associated with ADCA-DN, with potential implications for genes associated with related phenotypes.

Multimodal Exercise and Cognitive Training Program Improves Cognitive Function in Amnestic Mild Cognitive Impairment.

OBJECTIVE: To investigate the preliminary efficacy of a combined physical exercise + cognitive training intervention for older adults with amnestic mild cognitive impairment (aMCI). DESIGN: Randomized clinical trial. SETTING: Veteran Affairs Hospital, Palo Alto, CA. PARTICIPANTS: Sample included 72 community-dwelling volunteers (mean age 72.4 ± 9.5) diagnosed with aMCI. INTERVENTION: Participants were randomized to either a combined aerobic and resistance exercise + cognitive training (CARE+CT) or stretching exercise + CT (SE+CT). MEASUREMENTS: Primary outcomes included intervention specific assessments of word list and name-face recall. Secondary cognitive outcomes included standardized composite scores that reflect cognitive domains (e.g., learning and memory, executive function, processing speed, visuospatial ability, language). Secondary physiological outcomes included VO2 max and functional capacity (e.g., distance walked 6-minute walk test). APOE and BDNF were determined from whole blood samples. RESULTS: Controlling for age and employment status, linear mixed effects models revealed that all participants experienced significant improvement in the delayed recall of word list, learning and memory and executive function. Only the CARE+CT condition had significant improvement in processing speed and functional capacity. APOE4 status impacted cognitive benefits of those in the SE+CT condition. CONCLUSIONS: Results provide preliminary support for combined exercise and cognitive training interventions for older adults with aMCI. Further research is needed to understand the mechanisms involved as well as the impact of these interventions in diverse samples. TRIAL REGISTRATION: ClinicalTrials.gov Identifier: NCT01962038.

Autism genetics: opportunities and challenges for clinical translation.

Genetic studies have revealed the involvement of hundreds of gene variants in autism. Their risk effects are highly variable, and they are frequently related to other conditions besides autism. However, many different variants converge on common biological pathways. These findings indicate that aetiological heterogeneity, variable penetrance and genetic pleiotropy are pervasive characteristics of autism genetics. Although this advancing insight should improve clinical care, at present there is a substantial discrepancy between research knowledge and its clinical application. In this Review, we discuss the current challenges and opportunities for the translation of autism genetics knowledge into clinical practice.

Assembly of functionally integrated human forebrain spheroids.

The development of the nervous system involves a coordinated succession of events including the migration of GABAergic (γ-aminobutyric-acid-releasing) neurons from ventral to dorsal forebrain and their integration into cortical circuits. However, these interregional interactions have not yet been modelled with human cells. Here we generate three-dimensional spheroids from human pluripotent stem cells that resemble either the dorsal or ventral forebrain and contain cortical glutamatergic or GABAergic neurons. These subdomain-specific forebrain spheroids can be assembled in vitro to recapitulate the saltatory migration of interneurons observed in the fetal forebrain. Using this system, we find that in Timothy syndrome-a neurodevelopmental disorder that is caused by mutations in the CaV1.2 calcium channel-interneurons display abnormal migratory saltations. We also show that after migration, interneurons functionally integrate with glutamatergic neurons to form a microphysiological system. We anticipate that this approach will be useful for studying neural development and disease, and for deriving spheroids that resemble other brain regions to assemble circuits in vitro.

Integrated functional genomic analyses of Klinefelter and Turner syndromes reveal global network effects of altered X chromosome dosage.

In both Turner syndrome (TS) and Klinefelter syndrome (KS) copy number aberrations of the X chromosome lead to various developmental symptoms. We report a comparative analysis of TS vs. KS regarding differences at the genomic network level measured in primary samples by analyzing gene expression, DNA methylation, and chromatin conformation. X-chromosome inactivation (XCI) silences transcription from one X chromosome in female mammals, on which most genes are inactive, and some genes escape from XCI. In TS, almost all differentially expressed escape genes are down-regulated but most differentially expressed inactive genes are up-regulated. In KS, differentially expressed escape genes are up-regulated while the majority of inactive genes appear unchanged. Interestingly, 94 differentially expressed genes (DEGs) overlapped between TS and female and KS and male comparisons; and these almost uniformly display expression changes into opposite directions. DEGs on the X chromosome and the autosomes are coexpressed in both syndromes, indicating that there are molecular ripple effects of the changes in X chromosome dosage. Six potential candidate genes (RPS4X, SEPT6, NKRF, CX0rf57, NAA10, and FLNA) for KS are identified on Xq, as well as candidate central genes on Xp for TS. Only promoters of inactive genes are differentially methylated in both syndromes while escape gene promoters remain unchanged. The intrachromosomal contact map of the X chromosome in TS exhibits the structure of an active X chromosome. The discovery of shared DEGs indicates the existence of common molecular mechanisms for gene regulation in TS and KS that transmit the gene dosage changes to the transcriptome.

Preparing the Next Generation of Academic Researchers During the Pandemic: Lessons from a National Mental Health Research Postdoctoral Fellowship.

OBJECTIVE: The COVID-19 pandemic has severely disrupted all aspects of academic medicine, including post-doctoral research fellowship training. The current survey examined ways in which research fellows across 28 U.S. nationally diverse sites have been impacted. METHODS: Survey participants included 62 M.D. and Ph.D. post-doctoral fellows and 27 local fellowship center directors within the Veterans Affairs (VA) Advanced Fellowship in Mental Illness Research and Treatment (MIRT), a national fellowship program tasked to develop academic clinician researchers within the field of mental health. Survey questions focused on productivity and challenges experienced by fellows during the pandemic. RESULTS: Half of fellows reported working entirely off-site during the COVID-19 pandemic. All fellows reported some level of disruption in productivity during the pandemic; 73% reported a disruption in data collection, 69% reported decreased scholarly output, 41% reported disruption in grant writing, and 73% reported disruption in ability to provide clinical care. Yet, the majority of fellows (66%) reported not having to change their research goals, pivoting to telehealth-based data collection, and employing extant data for research projects and peer-reviewed publications. CONCLUSIONS: The results of the fellow and director surveys highlight the associated disruption of the COVID-19 pandemic on fellowship-related activities and parallel ingenuity of programs to continue conducting research and clinical services in a modified fashion. While many research goals continued unabated, the findings suggest alterations in data collection methodology and a focus on using extant data, which may have a residual influence on future early career research grant applications.

Genetic and environmental influences on structural brain measures in twins with autism spectrum disorder.

Atypical growth patterns of the brain have been previously reported in autism spectrum disorder (ASD) but these alterations are heterogeneous across individuals, which may be associated with the variable effects of genetic and environmental influences on brain development. Monozygotic (MZ) and dizygotic (DZ) twin pairs with and without ASD (aged 6-15 years) were recruited to participate in this study. T1-weighted MRIs (n = 164) were processed with FreeSurfer to evaluate structural brain measures. Intra-class correlations were examined within twin pairs and compared across diagnostic groups. ACE modeling was also completed. Structural brain measures, including cerebral and cerebellar gray matter (GM) and white matter (WM) volume, surface area, and cortical thickness, were primarily influenced by genetic factors in TD twins; however, mean curvature appeared to be primarily influenced by environmental factors. Similarly, genetic factors accounted for the majority of variation in brain size in twins with ASD, potentially to a larger extent regarding curvature and subcortical GM; however, there were also more environmental contributions in twins with ASD on some structural brain measures, such that cortical thickness and cerebellar WM volume were primarily influenced by environmental factors. These findings indicate potential neurobiological outcomes of the genetic and environmental risk factors that have been previously associated with ASD and, although preliminary, may help account for some of the previously outlined neurobiological heterogeneity across affected individuals. This is especially relevant regarding the role of genetic and environmental factors in the development of ASD, in which certain brain structures may be more sensitive to specific influences.

Genetic and Environmental Influences on Lobar Brain Structures in Twins With Autism.

This investigation examined whether the variation of cerebral structure is associated with genetic or environmental factors in children with autism spectrum disorder (ASD) compared with typically developing (TD) controls. T1-weighted magnetic resonance imaging scans were obtained from twin pairs (aged 6-15 years) in which at least one twin was diagnosed with ASD or both were TD. Good quality data were available from 30 ASD, 18 discordant, and 34 TD pairs (n = 164). Structural measures (volume, cortical thickness, and surface area) were generated with FreeSurfer, and ACE modeling was completed. Lobar structures were primarily genetically mediated in TD twins (a2 = 0.60-0.89), except thickness of the temporal (a2 = 0.33 [0.04, 0.63]) and occipital lobes (c2 = 0.61 [0.45, 0.77]). Lobar structures were also predominantly genetically mediated in twins with ASD (a2 = 0.70-1.00); however, thickness of the frontal (c2 = 0.81 [0.71, 0.92]), temporal (c2 = 0.77 [0.60, 0.93]), and parietal lobes (c2 = 0.87 [0.77, 0.97]), and frontal gray matter (GM) volume (c2 = 0.79 [0.63, 0.95]), were associated with environmental factors. Conversely, occipital thickness (a2 = 0.93 [0.75, 1.11]) did not exhibit the environmental contributions that were found in controls. Differences in GM volume were associated with social communication impairments for the frontal (r = 0.52 [0.18, 0.75]), temporal (r = 0.61 [0.30, 0.80]), and parietal lobes (r = 0.53 [0.19, 0.76]). To our knowledge, this is the first investigation to suggest that environmental factors influence GM to a larger extent in children with ASD, especially in the frontal lobe.

Genetic and environmental influences on corticostriatal circuits in twins with autism

Background: Corticostriatal circuits (CSC) have been implicated in the presentation of some restricted and repetitive behaviours (RRBs) in children with autism-spectrum disorder (ASD), and preliminary evidence suggests that disruptions in these pathways may be associated with differences in genetic and environmental influences on brain development. The objective of this investigation was to examine the impact of genetic and environmental factors on CSC regions in twins with and without ASD and to evaluate their relationship with the severity of RRBs. Methods: We obtained T1-weighted MRIs from same-sex monozygotic and dizygotic twin pairs, aged 6­15 years. Good-quality data were available from 48 ASD pairs (n = 96 twins; 30 pairs concordant for ASD, 15 monozygotic and 15 dizygotic; 18 pairs discordant for ASD, 4 monozygotic and 14 dizygotic) and 34 typically developing control pairs (n = 68 twins; 20 monozygotic and 14 dizygotic pairs). We generated structural measures of the orbitofrontal cortex (OFC), anterior cingulate cortex (ACC), caudate, putamen, pallidum and thalamus using FreeSurfer. Twin pair comparisons included intraclass correlation analyses and ACE modelling (a2 = additive genetics; c2 = common or shared environment; e2 = unique or nonshared environment). We also assessed correlations with RRB severity. Results: Structural variation in CSC regions was predominantly genetically mediated in typically developing twins (a2 = 0.56 to 0.87), except for ACC white matter volume (a2 = 0.42, 95% confidence interval [CI] 0.08 to 0.77). We also observed similar magnitudes of genetic influence in twins with ASD (a2 = 0.65 to 0.97), but the cortical thickness of the ACC (c2 = 0.44, 95% CI 0.22 to 0.66) and OFC (c2 = 0.60, 95% CI 0.25 to 0.95) was primarily associated with environmental factors in only twins with ASD. Twin pair differences in OFC grey matter volume were also correlated with RRB severity and were predominantly environmentally mediated. Limitations: We obtained MRIs on 2 scanners, and analytical approaches could not identify specific genetic and environmental factors. Conclusion: Genetic factors primarily contribute to structural variation in subcortical CSC regions, regardless of ASD, but environmental factors may exert a greater influence on the development of grey matter thickness in the OFC and ACC in children with ASD. The increased vulnerability of OFC grey matter to environmental influences may also mediate some heterogeneity in RRB severity in children with ASD.

The 5-HTTLPR long allele predicts two-year longitudinal increases in cortisol and declines in verbal memory in older adults.

OBJECTIVES: The short form or s-allele variant of the serotonin transporter polymorphism (5-HTTLPR), as compared with the long-form or l-allele variant, has been associated with the presence of cognitive dysfunction, and particularly memory impairment in older adults. This body of cross-sectional work has culminated in the hypothesis that presence of the s-allele predicts greater memory decline in older adults. Yet, to date, there are no longitudinal studies that have investigated this issue. METHODS/DESIGN: Here, we examine 109 community-dwelling older adults (mean and SD of age = 70.7 ± 8.7 years) who underwent blood draw for genotyping, cognitive, and psychological testing at baseline, 12-, and 24-monthfollow-ups. RESULTS: Multilevel modeling found that s-allele carriers (ss or ls) performed worse than ll homozygotes at baseline on delayed verbal recall. Yet, s-allele carriers' memory performance was stable over the two-yearfollow-up period, while l-allele homozygotes experienced significant memory decline. l-allele homozygote status was associated with both increased cortisol and decreased memory over time, resulting in attenuated verbal memory performance differences compared to s-allele carriers with age. CONCLUSIONS: Overall, our findings do not support the hypothesis that presence of the 5-HTTLPRs-allele is a marker for memory decline in older adults. J Am Geriatr Soc 68:-, 2020.

Sleep-wake disorders in Alzheimer's disease: further genetic analyses in relation to objective sleep measures.

This paper presents updated analyses on the genetic associations of sleep disruption in individuals with Alzheimer's disease (AD). We published previously a study of the association between single nucleotide polymorphisms (SNPs) found in eight genes related to circadian rhythms and objective measures of sleep-wake disturbances in 124 individuals with AD. Here, we present new relevant analyses using polygenic risk scores (PRS) and variable number tandem repeats (VNTRs) enumerations. PRS were calculated using the genetic data from the original participants and relevant genome wide association studies (GWAS). VNTRs for the same circadian rhythm genes studied with SNPs were obtained from a separate cohort of participants using whole genome sequencing (WGS). Objectively (wrist actigraphy) determined wake after sleep onset (WASO) was used as a measure of sleep disruption. None of the PRS were associated with sleep disturbance. Computer analyses using VNTRseek software generated a total of 30 VNTRs for the circadian-related genes but none appear relevant to our objective sleep measure. In addition, of 71 neurotransmitter function-related genes, 29 genes had VNTRs that differed from the reference VNTR, but it was not clear if any of these might affect circadian function in AD patients. Although we have not found in either the current analyses or in our previous published analyses of SNPs any direct linkages between identified genetic factors and WASO, research in this area remains in its infancy.

SHANK3 and IGF1 restore synaptic deficits in neurons from 22q13 deletion syndrome patients.

Phelan-McDermid syndrome (PMDS) is a complex neurodevelopmental disorder characterized by global developmental delay, severely impaired speech, intellectual disability, and an increased risk of autism spectrum disorders (ASDs). PMDS is caused by heterozygous deletions of chromosome 22q13.3. Among the genes in the deleted region is SHANK3, which encodes a protein in the postsynaptic density (PSD). Rare mutations in SHANK3 have been associated with idiopathic ASDs, non-syndromic intellectual disability, and schizophrenia. Although SHANK3 is considered to be the most likely candidate gene for the neurological abnormalities in PMDS patients, the cellular and molecular phenotypes associated with this syndrome in human neurons are unknown. We generated induced pluripotent stem (iPS) cells from individuals with PMDS and autism and used them to produce functional neurons. We show that PMDS neurons have reduced SHANK3 expression and major defects in excitatory, but not inhibitory, synaptic transmission. Excitatory synaptic transmission in PMDS neurons can be corrected by restoring SHANK3 expression or by treating neurons with insulin-like growth factor 1 (IGF1). IGF1 treatment promotes formation of mature excitatory synapses that lack SHANK3 but contain PSD95 and N-methyl-D-aspartate (NMDA) receptors with fast deactivation kinetics. Our findings provide direct evidence for a disruption in the ratio of cellular excitation and inhibition in PMDS neurons, and point to a molecular pathway that can be recruited to restore it.

Serotonin transporter polymorphism, depressive symptoms, and emotional impulsivity among advanced breast cancer patients.

PURPOSE: This study tested a theory linking a marker of low serotonergic function to both depression and impulsivity in a sample of advanced breast cancer patients, among whom elevated depressive symptoms and difficulty regulating emotions are commonly reported. METHODS: A total of 95 patients provided blood samples for serotonin transporter polymorphic region of the gene (5-HTTLPR) and completed questionnaires that measured depressive symptoms and emotional impulsivity. RESULTS: Structural equation modeling revealed that the s allele of 5-HTTLPR was related to greater depressive symptoms (ß = .20, p < .042) but only marginally to greater emotional impulsivity (ß = .19, p < .068). Depressive symptoms and emotional impulsivity were positively related (ß = .33, p < .003). Further tests explored possible mediation from genotype to one psychological variable via the other. Results suggest that depressive symptoms, particularly perceived interpersonal rejection, may be a pathway linking genotype to emotional impulsivity. CONCLUSIONS: Findings provide the first evidence that low serotonergic function contributes to both depression and impulsivity within a clinically meaningful sample. Furthermore, the link of s allele of 5-HTTLPR to emotional impulsivity was mediated by depressive symptoms, particularly perceptions of social rejection. Findings have implications for advanced breast cancer patients' treatment decision.

Using induced pluripotent stem cells to investigate cardiac phenotypes in Timothy syndrome.

Individuals with congenital or acquired prolongation of the QT interval, or long QT syndrome (LQTS), are at risk of life-threatening ventricular arrhythmia. LQTS is commonly genetic in origin but can also be caused or exacerbated by environmental factors. A missense mutation in the L-type calcium channel Ca(V)1.2 leads to LQTS in patients with Timothy syndrome. To explore the effect of the Timothy syndrome mutation on the electrical activity and contraction of human cardiomyocytes, we reprogrammed human skin cells from Timothy syndrome patients to generate induced pluripotent stem cells, and differentiated these cells into cardiomyocytes. Electrophysiological recording and calcium (Ca(2+)) imaging studies of these cells revealed irregular contraction, excess Ca(2+) influx, prolonged action potentials, irregular electrical activity and abnormal calcium transients in ventricular-like cells. We found that roscovitine, a compound that increases the voltage-dependent inactivation of Ca(V)1.2 (refs 6-8), restored the electrical and Ca(2+) signalling properties of cardiomyocytes from Timothy syndrome patients. This study provides new opportunities for studying the molecular and cellular mechanisms of cardiac arrhythmias in humans, and provides a robust assay for developing new drugs to treat these diseases.

Plasma oxytocin concentrations and OXTR polymorphisms predict social impairments in children with and without autism spectrum disorder.

The neuropeptide oxytocin (OXT) and its receptor (OXTR) regulate social functioning in animals and humans. Initial clinical research suggests that dysregulated plasma OXT concentrations and/or OXTR SNPs may be biomarkers of social impairments in autism spectrum disorder (ASD). We do not know, however, whether OXT dysregulation is unique to ASD or whether OXT biology influences social functioning more generally, thus contributing to, but not causing, ASD phenotypes. To distinguish between these possibilities, we tested in a child ASD cohort, which included unaffected siblings and unrelated neurotypical controls (ages 3-12 y; n = 193), whether plasma OXT concentrations and OXTR SNPs (i) interact to produce ASD phenotypes, (ii) exert differential phenotypic effects in ASD vs. non-ASD children, or (iii) have similar phenotypic effects independent of disease status. In the largest cohort tested to date, we found no evidence to support the OXT deficit hypothesis of ASD. Rather, OXT concentrations strongly and positively predicted theory of mind and social communication performance in all groups. Furthermore, OXT concentrations showed significant heritability between ASD-discordant siblings (h(2) = 85.5%); a heritability estimate on par with that of height in humans. Finally, carriers of the "G" allele of rs53576 showed impaired affect recognition performance and carriers of the "A" allele of rs2254298 exhibited greater global social impairments in all groups. These findings indicate that OXT biology is not uniquely associated with ASD, but instead exerts independent, additive, and highly heritable influences on individual differences in human social functioning, including the severe social impairments which characterize ASD.

Genome wide analysis of narcolepsy in China implicates novel immune loci and reveals changes in association prior to versus after the 2009 H1N1 influenza pandemic.

Previous studies in narcolepsy, an autoimmune disorder affecting hypocretin (orexin) neurons and recently associated with H1N1 influenza, have demonstrated significant associations with five loci. Using a well-characterized Chinese cohort, we refined known associations in TRA@ and P2RY11-DNMT1 and identified new associations in the TCR beta (TRB@; rs9648789 max P = 3.7 × 10(-9) OR 0.77), ZNF365 (rs10995245 max P = 1.2 × 10(-11) OR 1.23), and IL10RB-IFNAR1 loci (rs2252931 max P = 2.2 × 10(-9) OR 0.75). Variants in the Human Leukocyte Antigen (HLA)- DQ region were associated with age of onset (rs7744020 P = 7.9×10(-9) beta -1.9 years) and varied significantly among cases with onset after the 2009 H1N1 influenza pandemic compared to previous years (rs9271117 P = 7.8 × 10(-10) OR 0.57). These reflected an association of DQB1*03:01 with earlier onset and decreased DQB1*06:02 homozygosity following 2009. Our results illustrate how genetic association can change in the presence of new environmental challenges and suggest that the monitoring of genetic architecture over time may help reveal the appearance of novel triggers for autoimmune diseases.

ImmunoChip study implicates antigen presentation to T cells in narcolepsy.

Recent advances in the identification of susceptibility genes and environmental exposures provide broad support for a post-infectious autoimmune basis for narcolepsy/hypocretin (orexin) deficiency. We genotyped loci associated with other autoimmune and inflammatory diseases in 1,886 individuals with hypocretin-deficient narcolepsy and 10,421 controls, all of European ancestry, using a custom genotyping array (ImmunoChip). Three loci located outside the Human Leukocyte Antigen (HLA) region on chromosome 6 were significantly associated with disease risk. In addition to a strong signal in the T cell receptor alpha (TRA@), variants in two additional narcolepsy loci, Cathepsin H (CTSH) and Tumor necrosis factor (ligand) superfamily member 4 (TNFSF4, also called OX40L), attained genome-wide significance. These findings underline the importance of antigen presentation by HLA Class II to T cells in the pathophysiology of this autoimmune disease.

Mapping autism risk loci using genetic linkage and chromosomal rearrangements.

Autism spectrum disorders (ASDs) are common, heritable neurodevelopmental conditions. The genetic architecture of ASDs is complex, requiring large samples to overcome heterogeneity. Here we broaden coverage and sample size relative to other studies of ASDs by using Affymetrix 10K SNP arrays and 1,181 [corrected] families with at least two affected individuals, performing the largest linkage scan to date while also analyzing copy number variation in these families. Linkage and copy number variation analyses implicate chromosome 11p12-p13 and neurexins, respectively, among other candidate loci. Neurexins team with previously implicated neuroligins for glutamatergic synaptogenesis, highlighting glutamate-related genes as promising candidates for contributing to ASDs.

Integrated systems analysis reveals a molecular network underlying autism spectrum disorders.

Autism is a complex disease whose etiology remains elusive. We integrated previously and newly generated data and developed a systems framework involving the interactome, gene expression and genome sequencing to identify a protein interaction module with members strongly enriched for autism candidate genes. Sequencing of 25 patients confirmed the involvement of this module in autism, which was subsequently validated using an independent cohort of over 500 patients. Expression of this module was dichotomized with a ubiquitously expressed subcomponent and another subcomponent preferentially expressed in the corpus callosum, which was significantly affected by our identified mutations in the network center. RNA-sequencing of the corpus callosum from patients with autism exhibited extensive gene mis-expression in this module, and our immunochemical analysis showed that the human corpus callosum is predominantly populated by oligodendrocyte cells. Analysis of functional genomic data further revealed a significant involvement of this module in the development of oligodendrocyte cells in mouse brain. Our analysis delineates a natural network involved in autism, helps uncover novel candidate genes for this disease and improves our understanding of its molecular pathology.

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.