Influence of the COMT Genotype on Working Memory and Brain Activity Changes During Development

Background: The Valine158Methionine (Val158Met) polymorphism of the COMT gene leads to lower enzymatic activity and higher dopamine availability in Met carriers. The Met allele is associated with better performance and reduced prefrontal cortex activation during working memory (WM) tasks in adults. Dopaminergic system changes during adolescence may lead to a reduction of basal dopamine levels, potentially affecting Met allele benefits during development. Methods: We investigated the association of COMT genotype with behavioral (n = 322) and magnetic resonance imaging data (n = 81–84) collected during performance of a visuospatial WM task and potential changes in these effects during development (reflected in age × genotype interactions). Data were collected from a cross-sectional and longitudinal typically developing sample of 6- to 20-year-olds. Results: Visuospatial WM capacity exhibited an age × genotype interaction, with a benefit of the Met allele emerging after 10 years of age. There was a parallel age × genotype interaction on WM-related activation in the right inferior frontal gyrus and intraparietal sulcus (IPS), with increases in activation with age in the Val/Val group only. Main effects of COMT genotype were also observed in the IPS, with greater gray matter volumes bilaterally and greater right IPS activation in the Val/Val group compared with the Met carriers. Conclusions: These results suggest that COMT genotype effects on WM brain activity and behavior are not static during development. The full developmental picture should be considered when trying to understand the impact of genetic polymorphisms on the mature cognition of healthy adult or psychiatric populations

How might stress contribute to increased risk for schizophrenia in children with chromosome 22q11.2 deletion syndrome?

The most common human microdeletion occurs at chromosome 22q11.2. The associated syndrome (22q11.2DS) has a complex and variable phenotype with a high risk of schizophrenia. While the role of stress in the etiopathology of schizophrenia has been under investigation for over 30 years (Walker et al. 2008), the stress–diathesis model has yet to be investigated in children with 22q11.2DS. Children with 22q11.2DS face serious medical, behavioral, and socioemotional challenges from infancy into adulthood. Chronic stress elevates glucocorticoids, decreases immunocompetence, negatively impacts brain development and function, and is associated with psychiatric illness in adulthood. Drawing knowledge from the extant and well-developed anxiety and stress literature will provide invaluable insight into the complex etiopathology of schizophrenia in people with 22q11.2DS while suggesting possible early interventions. Childhood anxiety is treatable and stress coping skills can be developed thereby improving quality of life in the short-term and potentially mitigating the risk of developing psychosis

The etiology of ADHD

Attention Deficit/Hyperactivity Disorder (“ADHD”) is a complex multi-factorial disorder that was first described in the late 1800s as a defect in moral control. By the early 1900s, ADHD shifted away from being a behavioral-based to a neurobiological-based disorder. During this period, individuals with ADHD were classified as having minimal brain damage. Early studies focused on the clinical presentation of ADHD. As advances in neuroimaging and molecular marker techniques started to develop, researchers were able to focus more on the neurobiological aspects of ADHD. This shift was instrumental to both the diagnosis and treatment of ADHD. This paper surveys the existing literature on ADHD in an attempt to elucidate its etiology. While several areas of research seem promising, so far, no single major contributor to ADHD has been identified. This paper first looks at the history behind ADHD. The historical background was instrumental in directing the course of ADHD research. Next, the Diagnostic and Statistical Manual of Mental Disorders (“DSM”) is examined with a focus on the changes made to DSM-IV and reflected in DSM-V. While DSM is a valuable diagnostic tool, its purpose in elucidating the etiology behind ADHD is questionable. Despite that, discussion of the DSM is necessary as it is impossible to study a disorder without delineating the normal from the abnormal. What follows this discussion is a brief overview of comorbidities that are often associated, and possibly share, a common etiology with ADHD. The paper then examines the theories promulgated by researchers as to the neurobiological basis of ADHD. This examination is followed by a discussion of recent findings into the pathology behind ADHD, which mainly centers around differences in brain structure and connectivity. Further analysis of these studies reveals that sex plays an instrumental role in the type of brain abnormalities found in ADHD children. In addition, delays in brain development are analyzed, and age is discussed as a factor in the presentation of ADHD. This paper goes on to examine genetics as a contributor to the etiology of ADHD. This examination proves fruitful as several genes of interest seem to indicate a hereditary component of ADHD. Finally, treatment options such as psychosocial therapy and medications that help ADHD patients maintain a quality of life, are discussed. By studying the mechanism of action underlying these medications, additional clues as to the etiology of ADHD may be discovered. There is still a long way to go before a complete picture of ADHD emerges. Already, studies are showing that race and environmental factors play a role in how ADHD presents. These two areas have rarely been studied and doing so will only serve to enhance the current understanding of ADHD. Despite an incomplete picture, the scientific community has come a long way from the 1800s where ADHD was thought to result from a defect in moral control. With early diagnosis and proper treatment, the ADHD individuals of today can live a life as close to that of their neurotypical peers as possible

Velo-Cardio-Facial Syndrome

Velocardiofacial syndrome (VCFS), also known as DiGeorge, conotruncal anomaly face, and Cayler syndromes, is caused by a microdeletion in the long arm of Chromosome 22. We review the history of the syndrome from the first clinical reports almost half a century ago to the current intriguing molecular findings associating genes from the microdeletion region and the physical and neuropsychiatric phenotype of the syndrome. Velocardiofacial syndrome has a wide spectrum of more than 200 physical manifestations including palate and cardiac anomalies. Yet, the most challenging manifestations of VCFS are the learning disabilities and neuropsychiatric disorders. As VCFS is relatively common and as up to one third of the participants with VCFS develop schizophrenia-like psychotic disorder, the syndrome is the most commonly known genetic risk factor to schizophrenia. Identifying the genetic, cognitive, and psychiatric risk factors for VCFS-schizophrenia is under the focus of intensive research

The Role of COMT in Schizophrenic-Like Cognitive Impairment and Social Functioning in Children with 22q11 Deletion Syndrome

Schizophrenia is a severe psychiatric disorder that is hypothesized to represent the most extreme manifestation of a continuum of impairment referred to as schizotypy. As such, many of the cognitive, clinical, behavioral, and neuroanatomical features of schizophrenia should be present and detectable in nonpsychotic individuals who share this vulnerability. Recent findings have led to a renewed interest in the role that the gene that codes for catechol-O-methyltransferase (COMT) plays in the development and expression of schizotypy and schizophrenia. Specifically, an amino-acid polymorphism (Val158Met) in the COMT gene has been associated with schizophrenia based on linkage and association studies, with schizotypy in nonpsychotic adults, and with performance on dopamine-mediated prefrontal functioning in healthy adults and in patients with schizophrenia. Since abnormal functioning in dopaminergic pathways is thought to be associated with schizophrenia, COMT activity may play a role in schizophrenia pathogenesis and expression. The COMT gene is housed at 22q11.2, which maps to the commonly deleted region in 22q11 Deletion Syndrome (22q11DS), a syndrome that is associated with a highly elevated risk for the development of psychosis. The present study investigated the relationship of COMT genotype with neuropsychological impairment and social functioning in a nonpsychotic sample of children with 22q11DS. As hypothesized, participants with the Val allele performed worse on some measures of prefrontal functioning than participants with the Met allele. Additionally, participants with the Val allele exhibited schizophrenic-like social and behavioral deficits. Finally, associations between social and cognitive functioning and a haplotype that has been linked to schizophrenia were examined in patients with 22q11DS

White matter microstructure in 22q11 deletion syndrome: a pilot diffusion tensor imaging and voxel-based morphometry study of children and adolescents

Young people with 22q11 Deletion Syndrome (22q11DS) are at substantial risk for developing psychosis and have significant differences in white matter (WM) volume. However, there are few in vivo studies of both WM microstructural integrity (as measured using Diffusion Tensor (DT)-MRI) and WM volume in the same individual. We used DT-MRI and structural MRI (sMRI) with voxel based morphometry (VBM) to compare, respectively, the fractional anisotropy (FA) and WM volume of 11 children and adolescents with 22q11DS and 12 controls. Also, within 22q11DS we related differences in WM to severity of schizotypy, and polymorphism of the catechol-O-methyltransferase (COMT) gene. People with 22q11DS had significantly lower FA in inter-hemispheric and brainstem and frontal, parietal and temporal lobe regions after covarying for IQ. Significant WM volumetric increases were found in the internal capsule, anterior brainstem and frontal and occipital lobes. There was a significant negative correlation between increased schizotypy scores and reduced WM FA in the right posterior limb of internal capsule and the right body and left splenium of corpus callosum. Finally, the Val allele of COMT was associated with a significant reduction in both FA and volume of WM in the frontal lobes, cingulum and corpus callosum. Young people with 22q11DS have significant differences in both WM microstructure and volume. Also, there is preliminary evidence that within 22q11DS, some regional differences in FA are associated with allelic variation in COMT and may perhaps also be associated with schizotypy

Effects of Antenatal Maternal Depressive Symptoms and Socio-Economic Status on Neonatal Brain Development are Modulated by Genetic Risk

This study included 168 and 85 mother-infant dyads from Asian and United States of America cohorts to examine whether a genomic profile risk score for major depressive disorder (GPRSMDD) moderates the association between antenatal maternal depressive symptoms (or socio-economic status, SES) and fetal neurodevelopment, and to identify candidate biological processes underlying such association. Both cohorts showed a significant interaction between antenatal maternal depressive symptoms and infant GPRSMDD on the right amygdala volume. The Asian cohort also showed such interaction on the right hippocampal volume and shape, thickness of the orbitofrontal and ventromedial prefrontal cortex. Likewise, a significant interaction between SES and infant GPRSMDD was on the right amygdala and hippocampal volumes and shapes. After controlling for each other, the interaction effect of antenatal maternal depressive symptoms and GPRSMDD was mainly shown on the right amygdala, while the interaction effect of SES and GPRSMDD was mainly shown on the right hippocampus. Bioinformatic analyses suggested neurotransmitter/neurotrophic signaling, SNAp REceptor complex, and glutamate receptor activity as common biological processes underlying the influence of antenatal maternal depressive symptoms on fetal cortico-limbic development. These findings suggest gene-environment interdependence in the fetal development of brain regions implicated in cognitive-emotional function. Candidate biological mechanisms involve a range of brain region-specific signaling pathways that converge on common processes of synaptic development

BIOLOGICAL BASIS OF VARIABILITY IN DOPAMINE AVAILABILITY ON FRONTOSTRIATAL BRAIN FUNCTION IN ADOLESCENCE

Neurodevelopmental studies indicate a protracted development through adolescence of brain systems underlying incentive-driven behaviors including prefrontal cortex (PFC) and the striatum. These systems support the executive control of behavior as well as motivationally driven behaviors and may contribute to vulnerabilities in the emergence of psychopathology. The PFC and striatum may support cognition and motivation through the function of the neurotransmitter dopamine. Dopamine (DA) availability is increased during the adolescent period in human and animals and play an important role in mediating individual differences in risk-taking behaviors. This dissertation seeks to examine the moderating role of genetically mediated DA availability on frontostriatal brain function in adolescence. To this end, we genotyped individuals between the ages of 10 and 20 for common functional polymorphisms in three genes that have a direct influence on synaptic DA availability. In addition, we calculated a multilocus composite score in order to assess additive effects of our three genetic loci. We used functional magnetic resonance imaging (fMRI) to assess brain function. The purpose of our first study was to examine the integrity of frontostriatal networks using resting state functional connectivity. We then look more directly at the role of frontostriatal brain function on incentive-driven behaviors using a rewarded inhibitory control task that has a known developmental signature . Overall we found a moderating influence of DA availability on age-related changes in key frontostriatal circuitry suggesting that the maturation of brain function in adolescence may in part be mediated by inter-individual variability in DA signaling. Overall, the genotypes by age interactions highlight a unique DA-driven brain profile in adolescence. This suggests that a genetically mediated brain phenotype characterized in adolescence may differ significantly from that in adulthood. This has strong implications regarding the variability observed in adolescent risk-taking behaviors as well as predictions of later adult behavior

Associations between hypothalamic-pituitary-adrenal axis system gene variants and cortisol reactivity in preschoolers: Main effects and gene-environment interactions

Exposure to stressful events during early development has consistently been shown to produce long lasting effects on the hypothalamic-pituitary-adrenal (HPA) axis, which may increase vulnerability to mood and anxiety disorders. Recently reported genetic association studies indicate that these disorders may be influenced, in part, by gene-environment interactions (GxE) involving polymorphisms within the corticotrophin-releasing hormone and monoaminergic system genes. However, little is known about how genetic variants and life stress work to shape children’s neuroendocrine reactivity and emerging symptoms. Therefore, the aim of this thesis is to examine main effects of candidate genes and GxE on the neuroendocrine stress response and internalizing symptoms in a community sample of 409 preschoolers. In Chapter 2 analyses show associations between variants of the CRHR1 and CRHBP genes and children’s cortisol responses to a standardized laboratory stress task. I also found evidence for GxE, where variants of the CRH system genes moderated the impact of childhood stress on early-emerging symptoms of depression and anxiety. A functional polymorphism of the catechol-O-methyltransferase (COMT) gene, the val158met, has been implicated in the etiology of stress-related mood disorders. Therefore, in Chapter 3, I examined links between the val158met polymorphism, cortisol reactivity to stress, and internalizing symptoms. I found evidence for association between the val158met genotype and cortisol reactivity to stress. Additionally, the val158met genotype moderated the link between childhood stress and emerging symptoms of anxiety. Due to the proposed role of dopamine and serotonin gene polymorphisms in research on GxE in internalizing disorders, in Chapters 4 and 5, I examined whether associations between dopaminergic and serotonin candidate gene polymorphisms and childhood cortisol reactivity and internalizing symptoms were moderated by childhood life stress. Analyses showed evidence for GxE predicting children’s symptoms. Specifically, polymorphisms of DRD2 and DAT1 genes moderated the effect of childhood stress on emerging symptoms of anxiety. With regard to serotonin pathway polymorphisms, I found associations between the serotonin transporter promoter polymorphism (5-HTTLPR) and children’s anxious symptoms. Additionally, consistent with previously reported findings, the interaction between MAOA 30bp VNTR and childhood stress predicted child anxiety symptoms. Limitations of this work include a relatively small sample size for genetic analyses, as well as the examination of a limited number of markers at each gene. Additionally, I did not correct for multiple statistical tests in some analyses due to the hypothesis-driven nature of the work. Taken together, the analyses show the complex underpinnings of individual differences in stress regulation, and highlight specific genetic vulnerabilities that influence early psychophysiological reactivity, that may in turn contribute to the development of stress-related disorders later in development

Genetic Factors in the Regulation of Striatal and Extrastriatal Dopamine D2 Receptor Expression

Positron emission tomography (PET) studies on healthy individuals have revealed a marked interindividual variability in striatal dopamine D2 receptor density that can be partly accounted for by genetic factors. The examination of the extrastriatal lowdensity D2 receptor populations has been impeded by the lack of suitable tracers. However, the quantification of these D2 receptor populations is now feasible with recently developed PET radioligands. The objective of this thesis was to study brain neurobiological correlates of common functional genetic variants residing in candidate genes relevant for D2 receptor functioning. For this purpose, healthy subjects were studied with PET imaging using [11C]raclopride and [11C]FLB457 as radioligands. The candidate genes examined in this work were the human D2 receptor gene (DRD2) and the catechol-Omethyltransferase gene (COMT). The region-specific genotypic influences were explored by comparing D2 receptor binding properties in the striatum, the cortex and the thalamus. As an additional study objective, the relationship between cortical D2 receptor density and a cognitive phenotype i.e. verbal memory and learning was assessed. The main finding of this study was that DRD2 C957T genotype altered markedly D2 receptor density in the cortex and the thalamus whereas in the striatum the C957T genotype affected D2 receptor affinity, but not density. Furthermore, the A1 allele of the DRD2-related TaqIA polymorphism showed increased cortical and thalamic D2 receptor density, but had the opposite effect on striatal D2 receptor density. The DRD2 –141C Ins/Del or the COMT Val158Met genotypes did not change D2 receptor binding properties. Finally, unlike previously reported, cortical D2 receptor density did not show any significant correlation with verbal memory function. The results of this study suggest that the C957T and the TaqIA genotypes have region-specific neurobiological correlates in brain dopamine D2 receptor availability in vivo. The biological mechanisms underlying these findings are unclear, but they may be related to the region-specific regulation of dopamine neurotranssion, gene/receptor expression and epigenesis. These findings contribute to the understanding of the genetic regulation of dopamine and D2 receptor-related brain functions in vivo in man. In addition, the results provide potentially useful endophenotypes for genetic research on psychiatric and neurological disorders.Siirretty Doriast