Genotype determining low catechol-O-methyltransferase activity as a risk factor for obsessive-compulsive disorder

The Neurobiological Underpinnings of Obsessive-Compulsive Symptoms in Psychosis, Translational Issues for Treatment-Resistant Schizophrenia

Almost 25% of schizophrenia patients suffer from obsessive-compulsive symptoms (OCS) considered a transdiagnostic clinical continuum. The presence of symptoms pertaining to both schizophrenia and obsessive-compulsive disorder (OCD) may complicate pharmacological treatment and could contribute to lack or poor response to the therapy. Despite the clinical relevance, no reviews have been recently published on the possible neurobiological underpinnings of this comorbidity, which is still unclear. An integrative view exploring this topic should take into account the following aspects: (i) the implication for glutamate, dopamine, and serotonin neurotransmission as demonstrated by genetic findings; (ii) the growing neuroimaging evidence of the common brain regions and dysfunctional circuits involved in both diseases; (iii) the pharmacological modulation of dopaminergic, serotoninergic, and glutamatergic systems as current therapeutic strategies in schizophrenia OCS; (iv) the recent discovery of midbrain dopamine neurons and dopamine D1- and D2-like receptors as orchestrating hubs in repetitive and psychotic behaviors; (v) the contribution of N-methyl-D-aspartate receptor subunits to both psychosis and OCD neurobiology. Finally, we discuss the potential role of the postsynaptic density as a structural and functional hub for multiple molecular signaling both in schizophrenia and OCD pathophysiology.

Catechol-O-methyltransferase (COMT) Val158Met Polymorphism and Susceptibility to Alcohol Dependence

Catechol-O-methyl transferase (COMT) enzyme catalyzes the metabolism of dopamine and other catechols in the brain. Several articles investigated catechol-O-methyltransferase (COMT) Val158Met polymorphism as risk factor for alcohol dependence (AD) but the results were inconclusive. The aim of present meta-analysis was to evaluate the association of Val158Met (COMT) polymorphism with AD. Authors performed keyword search of the 4 electronic databases-Pubmed, Google Scholar, Springer Link and Science Direct databases up to December 31, 2019. Total eighteen studies that investigated the association of Val158Met polymorphism with AD were retrieved. The pooled results from the meta-analysis (2278 AD cases and 3717 healthy controls) did not show association with AD using all 5 genetic models (allele contrast model: OR = 1.02, 95% CI = 0.90-1.14, p = 0.03; homozygote model: OR = 1.06, 95% CI = 0.81-1.38, p = 0.69; dominant model: OR = 0.99, 95% CI = 0.85-1.14, p = 0.87; co-dominant model: OR = 0.97, 95% CI = 0.86-1.11, p = 0.71; recessive model: OR = 1.05;95% CI = 0.85-1.29, p = 0.61). Results of subgroup analysis showed that Val158Met is not risk for AD in Asian and Caucasian population. In conclusion, COMT Val158Met is not a risk factor for alcohol dependence.

Genetic and epigenetic architecture of Obsessive-Compulsive Disorder: In search of possible diagnostic and prognostic biomarkers

Obsessive-Compulsive Disorder (OCD) is a prevalent and severe clinical condition whose hallmarks are excessive, unwanted thoughts (obsessions) and repetitive behaviors (compulsions). The onset of symptoms generally occurs during pre-adult life and typically affects subjects in different aspects of their life's, compromising social and professional relationships. Although robust evidence suggests a genetic component in the etiopathogenesis of OCD, the causes of the disorder are still not completely understood. It is thus of relevance to take into account how genes interact with environmental risk factors, thought to be mediated by epigenetic mechanisms. We here provide an overview of genetic and epigenetic mechanisms of OCD, focusing on the modulation of key central nervous system genes, in the attempt to suggest possible disease biomarkers.

Pharmacodynamic Gene Testing in Prader-Willi Syndrome

Prader-Willi syndrome (PWS) is a rare genetic disorder with a complex neurobehavioral phenotype associated with considerable psychiatric co-morbidity. This clinical case series, for the first time, describes the distribution and frequency of polymorphisms of pharmacodynamic genes (serotonin transporter, serotonin 2A and 2C receptors, catechol-o-methyltransferase, adrenergic receptor 2A, methylene tetrahydrofolate reductase, and human leucocytic antigens) across the two major molecular classes of PWS in a cohort of 33 referred patients who met medical criteria for testing. When results were pooled across PWS genetic subtypes, genotypic and allelic frequencies did not differ from normative population data. However, when the genetic subtype of PWS was examined, there were differences observed across all genes tested that may affect response to psychotropic medication. Due to small sample size, no statistical significance was found, but results suggest that pharmacodynamic gene testing should be considered before initiating pharmacotherapy in PWS. Larger scale studies are warranted.

An Investigation of the COMT Gene Val158Met Polymorphism in Patients Admitted to the Emergency Department Because of Synthetic Cannabinoid Use

Catechol-O-methyl transferase (COMT) enzyme has a role in the inactivation of catecholamine neurotransmitters. Functional polymorphism in the COMT gene has been reported to play an important role in schizophrenia, bipolar affective disorder, aggressive and antisocial behavior, suicide attempts and the pathogenesis of Parkinson's disease. In this study, we aimed to investigate the effect of the Vall58Met polymorphism of the COMT gene on substance use, and treatment history in patients with synthetic cannabinoid (SC) intoxication. The COMT enzyme Val158Met polymorphisms from DNA of 49 patients who were evaluated in the Emergency Department after SC use and 50 healthy control groups aged 18-45 years, were identified by polymerase chain reaction (PCR) and restriction fragment length polymorphism (RFLP) analyses as reported in the literature. Information regarding recurrent intake or hospitalization due to substance use was obtained from hospital records. Wild-type (WT) genotypes in 14 (28.6%) patients, heterozygous genotypes in 25 (51.0%) and homozygous genotypes in 10 (20.4%) patients were detected. Wild-type genotypes The homozygous genotype was found to be significantly higher in patients hospitalized due to drug addiction and substance use (p 0.008). The Vall58 Met polymorphism of the COMT gene was not found to be significant in the first use after substance intake, while a significant relationship was found in terms of this polymorphism in patients with substance addiction diagnosis and treatment history.

Pharmacogenetics of anxiety disorders

Anxiety disorders are common and disabling conditions the treatment of which remains a challenge. While different groups of medication are available for their treatment, a substantial proportion of patients remain refractory to pharmacotherapy. The reason for this variation in the individual response to treatment has yet to be understood; however genetic factors have been shown to play an important role. Up to now there have been limited publications about pharmacogenetics of anxiety disorders, compared to studies in depression. Published studies are focused on pharmacogenetics of antidepressants rather than being disease specific. This review summarizes pharmacogenetic findings related to the anxiolytic treatment response and their possible functional mechanisms. This inevitably focuses on genes involved in the pharmacodynamics of the medications used, along with some genes implicated in the disease process, as well as briefly mentioning genetic factors associated with psychotherapeutic response.

Role of the COMT gene Val158Met polymorphism in mental disorders: A review

The Val158Met polymorphism of the COMT gene is functional, easily detectable, and significantly related to metabolism of catecholamines, which underlie pathogenesis of a significant number of mental disorders. Evidence for the role of this polymorphism in schizophrenia, substance dependence, bipolar disorder, obsessive-compulsive disorder, anorexia nervosa and attention deficit hyperactivity disorder is summed up in this review article. The results make it unlikely that the COMT gene plays an important role in these mental disorders, although a minor effect can not be excluded. Future studies on the COMT gene in mentally ill subjects should be stratified by clinical subtypes of the disorder, gender and ethnicity. Studies of endophenotypes instead of the complex disorder seem to be another promising research strategy. Gene-gene and gene-environment interactions should also be considered. The COMT gene is probably not “a gene for” any mental disorder, but the Val158Met polymorphism appears to have pleiotropic effects on human behavior.

Catechol-O-methyltransferase gene Val158Met polymorphism and obsessive compulsive disorder susceptibility: a meta-analysis

Obsessive-compulsive disorder (OCD) is a common psychiatric disorder that affects approximately 1-3% of the general population. It is characterized by disabling obsessions (intrusive unwanted thoughts) and/or compulsions (ritualized repetitive behaviors). Catechol-O-methyltransferase (COMT) enzyme has an important role in inactivation of dopamine and higher dopamine levels may be implicated in OCD, hence COMT gene is a suitable candidate for OCD. Several case-control studies have evaluated the role of COMT Val 158Met (rs4680;472G- > A) polymorphism as a risk factor for OCD but the results remained inconclusive, hence present meta-analysis was designed to find out correct assessment. All studies that investigated the association of COMT gene Val158Met polymorphism with OCD risk, were considered in the present meta-analysis. Statistical analysis was performed with the software program MetaAnalyst. In the current meta-analysis, 14 case-control studies with 1435 OCD cases and 2753 healthy controls were included. The results indicated significant association between COMT Val158Met polymorphism and OCD risk using allele contrast, homozygote and dominant models (OR_{A vs G} = 1.14; 95% CI = 1.02-1.27; p = 0.01; OR_AAvs.GG = 1.33; 95% CI = 1.09-1.62, p = 0.004; OR_{AA + AGvs.GG} = 1.14; 95% CI = 1.0-1.32; p = 0.04). In subgroup analysis based on case gender, meta-analysis of male cases showed significant association using all five genetic models (OR_AAvsGG = 1.99; 95%CI = 1.42-2.59; p = <0.001; OR_{AA + AGvs.GG} = 1.59; 95% CI = 1.20-2.10; p = 0.001), but did not show any association between COMT Val 158Met polymorphism and OCD risk in females. In conclusion, results of present meta-analysis supports that the COMT Val158Met polymorphism is a risk factor for OCD especially for males.

Genetics of sex differences in neuroanatomy and function

Sex differences are observed at many distinct biologic levels, such as in the anatomy and functioning of the brain, behavior, and susceptibility to neuropsychiatric disorders. Previously, these differences were believed to entirely result from the secretion of gonadal hormones; however, recent research has demonstrated that differences are also the consequence of direct or nonhormonal effects of genes located on the sex chromosomes. This chapter reviews the four core genotype model that separates the effects of hormones and sex chromosomes and highlights a few genes that are believed to be partly responsible for sex dimorphism of the brain, in particular, the Sry gene. Genetics of the brain's neurochemistry is discussed and the susceptibility to certain neurologic and psychiatric disorders is reviewed. Lastly, we discuss the sex-specific genetic contribution in disorders of sexual development. The precise molecular mechanisms underlying these differences are currently not entirely known. An increased knowledge and understanding of the role of candidate genes will undeniably be of great aid in elucidating the molecular basis of sex-biased disorders and potentially allow for more sex-specific therapies.

Heterosis in COMT Val158Met Polymorphism Contributes to Sex-Differences in Children's Math Anxiety

Math anxiety (MA) is a phobic reaction to math activities, potentially impairing math achievement. Higher frequency of MA in females is explainable by the interaction between genetic and environmental factors. The molecular-genetic basis of MA has not been investigated. The COMT Val158Met polymorphism, which affects dopamine levels in the prefrontal cortex, has been associated with anxiety manifestations. The valine allele is associated with lower, and the methionine allele with higher, dopamine availability. In the present study, the effects of sex and COMT Val158Met genotypes on MA were investigated: 389 school children aged 7-12 years were assessed for intelligence, numerical estimation, arithmetic achievement and MA and genotyped for COMT Val158Met polymorphism. The Math Anxiety Questionnaire (MAQ) was used to assess the cognitive and affective components of MA. All genotype groups of boys and girls were comparable regarding genotype frequency, age, school grade, numerical estimation, and arithmetic abilities. We compared the results of all possible genetic models: codominance (Val/Val vs. Val/Met vs. Met/Met), heterosis (Val/Met vs. Val/Val plus Met/Met), valine dominance (Val/Val plus Val/Met vs. Met/Met), and methionine dominance (Met/Met plus Val/Met vs. Val/Val). Models were compared using AIC and AIC weights. No significant differences between girls and boys and no effects of the COMT Val158Met polymorphism on numerical estimation and arithmetic achievement were observed. Sex by genotype effects were significant for intelligence and MA. Intelligence scores were higher in Met/Met girls than in girls with at least one valine allele (valine dominance model). The best fitting model for MA was heterosis. In Anxiety Toward Mathematics, heterozygous individuals presented MA levels close to the grand average regardless of sex. Homozygous boys were significantly less and homozygous girls significantly more math anxious. Heterosis has been seldom explored, but in recent years has emerged as the best genetic model for some phenotypes associated with the COMT Val158Met polymorphism. This is the first study to investigate the genetic-molecular basis of MA.

Systematic review of co-occurring OCD and TD: Evidence for a tic-related OCD subtype?

OBJECTIVE

The aim of this review is to summarize the current knowledge of associated features of co-occurring obsessive-compulsive disorder (OCD) and tic disorders (TD) and to critically evaluate hypotheses regarding the nature of their comorbidity.

METHOD

We conducted a systematic review following PRISMA guidelines. To this aim, the PubMed, PsychInfo and ISI Web of Knowledge databases were searched up to August 30, 2018. For gender and age-of-onset we additionally conducted meta-analyses.

RESULTS

One hundred eighty-nine studies met inclusion criteria. We substantiate some acknowledged features and report evidence for differential biological mechanisms and treatment response. In general, studies were of limited methodological quality.

CONCLUSIONS

Several specific features are reliable associated with co-occurring OCD + TD. The field lacks methodological sound studies. The review found evidence against and in favor for different hypotheses regarding the nature of comorbidity of OCD and TD. This could indicate the existence of a stepwise model of co-morbidity, or could be an artefact of the low methodological quality of studies.

Haplotypic and Genotypic Association of Catechol-O-Methyltransferase rs4680 and rs4818 Polymorphisms and Treatment Resistance in Schizophrenia

Treatment-resistant schizophrenia (TRS) continues to be a challenge. It was related to different factors, including alterations in the activity of brain dopaminergic system, which could be influenced by the dopamine-degrading enzyme, catechol-O-methyltransferase (COMT). Variants of the COMT gene have been extensively studied as risk factors for schizophrenia; however, their association with TRS has been poorly investigated. The aim of the present study was to determine the haplotypic and genotypic association of COMT rs4680 and rs4818 polymorphisms with the presence of TRS. Overall, 931 Caucasian patients diagnosed with schizophrenia (386 females and 545 males) were included, while 270 participants met the criteria for TRS. In males, no significant haplotypic and genotypic associations between COMT rs4680 and rs4818 polymorphisms and TRS were detected. However, genotypic analyses demonstrated higher frequency of COMT rs4680 AA genotype carriers compared to G-allele carriers (p = 0.033) and higher frequency of COMT rs4818 CC genotype carriers than G-allele carriers (p = 0.014) in females with TRS. Haplotype analyses confirmed that the presence of the G allele in females was associated with lower risk of TRS. In women with TRS, the high activity G-G/G-G haplotype was rare, while carriers of other haplotypes were overrepresented (p = 0.009). Such associations of COMT rs4680 and rs4818 high-activity (G variants), as well as G-G/G-G haplotype, with the lower risk of TRS in females, but not in males, suggest significant, but sex-specific influence of COMT variants on the development of treatment-resistance in patients with schizophrenia. However, due to relatively low number of females, those findings require replication in a larger sample.

Dopaminergic and Serotonergic Genotypes and the Subjective Experiences of Hypnosis

Hypnotizability is related to the Val¹⁵⁸Met polymorphism of the COMT gene. The authors' aim was to find associations between candidate genes and subjective dimensions of hypnosis; 136 subjects participated in hypnosis and noninvasive DNA sampling. The phenomenological dimensions were tapped by the Archaic Involvement Measure (AIM), the Phenomenology of Consciousness Inventory (PCI), and the Dyadic Interactional Harmony Questionnaire (DIH). The main results were that the "Need of dependence" subscale of AIM was associated with the COMT genotypes. The GG subgroup showed higher scores, whereas AA had below average scores on the majority of the subjective measures. An association between the 5-HTTLPR polymorphism and the intimacy scores on the DIH was also evident. The effects are discussed in the social-psychobiological model of hypnosis.

Modification of the association between early adversity and obsessive-compulsive disorder by polymorphisms in the MAOA, MAOB and COMT genes

The monoamine oxidases (MAOA/B) and catechol-O-methyltransferase (COMT) enzymes break down regulatory components within serotonin and dopamine pathways, and polymorphisms within these genes are candidates for OCD susceptibility. Childhood trauma has been linked OCD psychopathology, but little attention has been paid to the interactions between genes and environment in OCD aetiology. This pilot study investigated gene-by-environment interactions between childhood trauma and polymorphisms in the MAOA, MAOB and COMT genes in OCD. Ten polymorphisms (MAOA: 3 variants, MAOB: 4 variants, COMT: 3 variants) were genotyped in a cohort of OCD patients and controls. Early-life trauma was assessed using the Childhood Trauma Questionnaire (CTQ). Gene-by-gene (GxG) and gene-by-environment interactions (GxE) of the variants and childhood trauma were assessed using logistic regression models. Significant GxG interactions were found between rs362204 (COMT) and two independent polymorphisms in the MAOB gene (rs1799836 and rs6651806). Haplotype associations for OCD susceptibility were found for MAOB. Investigation of GxE interactions indicated that the sexual abuse sub-category was significantly associated with all three genes in haplotype x environment interaction analyses. Preliminary findings indicate that polymorphisms within the MAOB and COMT genes interact resulting in risk for OCD. Childhood trauma interacts with haplotypes in COMT, MAOA and MAOB, increasing risk for OCD.

Genetics of anxiety: would the genome recognize the DSM?

The nosology of anxiety disorders has undergone substantial evolution over the past several decades. The modern classification of these disorders dates to the publication of Diagnostic and Statistical Manual-III (DSM-III) in 1980, but the validity of the current diagnostic categories has been the subject of controversy. Genetic research can help clarify the boundaries of diagnostic categories by examining the etiologic relationships among them. The question posed in the title of this article asks to what degree the DSM-IV definitions of the anxiety disorders are supported by the evolving body of research on the genetic basis of pathologic anxiety. With DSM-V on the horizon, there is a renewed imperative to examine the structure of these disorders. In this article, we address this issue by, first, providing a brief update about the current status of genetic research on anxiety disorders and then considering whether the evidence suggests that genetic influences conform to or transcend DSM definitions. Finally, we discuss future directions for the genetic dissection of anxiety disorders.

Childhood Trauma and COMT Genotype Interact to Increase Hippocampal Activation in Resilient Individuals

Both childhood trauma and a functional catechol-O-methyltransferase (COMT) genetic polymorphism have been associated with posttraumatic stress disorder (PTSD) and depression; however, it is still unclear whether the two interact and how this interaction relates to long-term risk or resilience. Imaging and genotype data were collected on 73 highly traumatized women. DNA extracted from saliva was used to determine COMT genotype (Val/Val, n = 38, Met carriers, n = 35). Functional MRI data were collected during a Go/NoGo task to investigate the neurocircuitry underlying response inhibition. Self-report measures of adult and childhood trauma exposure, PTSD and depression symptom severity, and resilience were collected. Childhood trauma was found to interact with COMT genotype to impact inhibition-related hippocampal activation. In Met carriers, more childhood trauma was associated with decreased hippocampal activation, whereas in the Val/Val group childhood trauma was related to increased hippocampal activation. Second, hippocampal activation correlated negatively with PTSD and depression symptoms and positively with trait resilience. Moreover, hippocampal activation mediated the relationship between childhood trauma and psychiatric risk or resilience in the Val/Val, but not in the Met carrier group. These data reveal a potential mechanism by which childhood trauma and COMT genotype interact to increase risk for trauma-related psychopathology or resilience. Hippocampal recruitment during inhibition may improve the ability to use contextual information to guide behavior, thereby enhancing resilience in trauma-exposed individuals. This finding may contribute to early identification of individuals at risk and suggests a mechanism that can be targeted in future studies aiming to prevent or limit negative outcomes.

A Framework for Understanding the Emerging Role of Corticolimbic-Ventral Striatal Networks in OCD-Associated Repetitive Behaviors

Significant interest in the mechanistic underpinnings of obsessive-compulsive disorder (OCD) has fueled research on the neural origins of compulsive behaviors. Converging clinical and preclinical evidence suggests that abnormal repetitive behaviors are driven by dysfunction in cortico-striatal-thalamic-cortical (CSTC) circuits. These findings suggest that compulsive behaviors arise, in part, from aberrant communication between lateral orbitofrontal cortex (OFC) and dorsal striatum. An important body of work focused on the role of this network in OCD has been instrumental to progress in the field. Disease models focused primarily on these regions, however, fail to capture an important aspect of the disorder: affective dysregulation. High levels of anxiety are extremely prevalent in OCD, as is comorbidity with major depressive disorder. Furthermore, deficits in processing rewards and abnormalities in processing emotional stimuli are suggestive of aberrant encoding of affective information. Accordingly, OCD can be partially characterized as a disease in which behavioral selection is corrupted by exaggerated or dysregulated emotional states. This suggests that the networks producing OCD symptoms likely expand beyond traditional lateral OFC and dorsal striatum circuit models, and highlights the need to cast a wider net in our investigation of the circuits involved in generating and sustaining OCD symptoms. Here, we address the emerging role of medial OFC, amygdala, and ventral tegmental area projections to the ventral striatum (VS) in OCD pathophysiology. The VS receives strong innervation from these affect and reward processing regions, and is therefore poised to integrate information crucial to the generation of compulsive behaviors. Though it complements functions of dorsal striatum and lateral OFC, this corticolimbic-VS network is less commonly explored as a potential source of the pathology underlying OCD. In this review, we discuss this network's potential role as a locus of OCD pathology and effective treatment.

No association between the COMT Val158Met polymorphism and the long-term clinical response in obsessive-compulsive disorder in the Japanese population

OBJECTIVE

Catechol-O-methyltransferase (COMT) is an enzyme that participates in the metabolic inactivation of dopamine and norepinephrine, and the Met allele of the COMT Val158Met polymorphism is associated with lower enzymatic activity. The purpose of the present study was to investigate whether this functional variant is associated with obsessive-compulsive disorder (OCD) and the clinical responses in OCD.

METHODS

We first performed a case-control association study between the COMT Val158Met polymorphism and OCD (171 cases and 944 controls). Then, we examined the association between this polymorphism and the clinical responses in 91 of the OCD patients.

RESULTS

Our study did not find a significant association between the Met allele and OCD risk or between the Met allele and clinical responses (p > 0.05).

CONCLUSION

The present case-control/pharmacogenetic study did not provide clear evidence that the COMT Val158Met polymorphism is a predictor of OCD or of OCD patients' clinical responses.

Altered inhibition-related frontolimbic connectivity in obsessive-compulsive disorder

BACKGROUND

Recent studies have shown that response inhibition is impaired in patients with obsessive-compulsive disorder and their unaffected siblings, suggesting that these deficits may be considered a cognitive endophenotype of obsessive-compulsive disorder. Structural and functional neural correlates of altered response inhibition have been identified in patients and siblings. This study aims to examine the functional integrity of the response inhibition network in patients with obsessive-compulsive disorder and their unaffected siblings.

METHODS

Forty-one unmedicated patients with obsessive-compulsive disorder, 17 of their unaffected siblings and 37 healthy controls performed a stop signal task during functional magnetic resonance imaging. Psycho-physiological interaction analysis was used to examine functional connectivity between the following regions of interest: the bilateral inferior frontal gyri, presupplementary motor area, subthalamic nuclei, inferior parietal lobes, anterior cingulate cortex, and amygdala. We then used dynamic causal modeling to investigate the directionality of the networks involved.

RESULTS

Patients, and to a lesser extent also their unaffected siblings, show altered connectivity between the inferior frontal gyrus and the amygdala during response inhibition. The follow-up dynamic causal modeling suggests a bottom-up influence of the amygdala on the inferior frontal gyrus in healthy controls, whereas processing occurs top-down in patients with obsessive-compulsive, and in both directions in siblings.

CONCLUSIONS

Our findings suggest that amygdala activation in obsessive-compulsive disorder interferes differently with the task-related recruitment of the inhibition network, underscoring the role of limbic disturbances in cognitive dysfunctions in obsessive-compulsive disorder.

Epistasis in the risk of human neuropsychiatric disease

Neuropsychiatric disease represents the ideal class of disease to assess the role of epistasis, as more genes are expressed in the brain than in any other tissue. In this chapter, two well-studied neuropsychiatric diseases are examined, Alzheimer's disease (AD) and schizophrenia, which have been shown to have multiple and, often, replicated interactions that associate with clinical endpoints or related phenotypes. In each case, a single gene is represented in a plurality of epistatic interactions, apolipoprotein E (APOE) for AD and catechol-O-methyltransferase for schizophrenia. Interestingly, of the two, only APOE has clear-cut and consistent evidence for a marginal association. Unraveling the underlying reasons is important in understanding both genetic etiology and architecture as well as how to use genetics to provide better personalized treatments.

Association of the catechol-O-methyltransferase val158met polymorphism and anxiety-related traits: a meta-analysis

OBJECTIVES

The aims of this study were (i) to examine genotypic association of the catechol-O-methyltransferase (COMT) val158met polymorphism with anxiety-related traits with a meta-analysis; (ii) to examine sex and ethnicity as moderators of the association; and (iii) to evaluate whether the association differed by particular anxiety traits.

METHODS

Association studies of the COMT val158met polymorphism and anxiety traits were identified from the PubMed or PsycInfo databases, conference abstracts, and listserv postings. Exclusion criteria were (a) pediatric samples, (b) exclusively clinical samples, and (c) samples selected for a nonanxiety phenotype. Standardized mean differences in anxiety between genotypes were aggregated to produce mean effect sizes across all available samples, and for subgroups stratified by sex and ethnicity (Whites vs. Asians). Construct-specific analysis was conducted to evaluate the association of COMT with neuroticism, harm avoidance, and behavioral inhibition.

RESULTS

Twenty-seven eligible studies (N=15 979) with available data were identified. Overall findings indicate sex-specific and ethnic-specific effects: valine homozygotes had higher neuroticism than methionine homozygotes in studies of White males [mean effect size(Equation is included in full-text article.)=0.13; 95% CI 0.02, 0.25; P=0.03], and higher harm avoidance in studies of Asian males ((Equation is included in full-text article.)=0.43; 95% CI 0.14, 0.72; P=0.004). No significant associations were found in women and effect sizes were diminished when studies were aggregated across ethnicity or anxiety traits.

CONCLUSION

This meta-analysis provides evidence for sex and ethnic differences in the association of the COMT val158met polymorphism with anxiety traits. Our findings contribute to current knowledge on the relation between prefrontal dopaminergic transmission and anxiety.

Epistasis between polymorphisms in COMT, ESR1, and GCH1 influences COMT enzyme activity and pain

Abnormalities in the enzymatic activity of catechol-O-methyltransferase (COMT) contribute to chronic pain conditions, such as temporomandibular disorders (TMD). Thus, we sought to determine the effects of polymorphisms in COMT and functionally related pain genes in the COMT pathway (estrogen receptor 1 [ESR1], guanosine-5-triphosphate cyclohydrolase 1 [GCH1], methylenetetrahydrofolate reductase [MTHFR]) on COMT enzymatic activity, musculoskeletal pain, and pain-related intermediate phenotypes among TMD cases and healthy control subjects. Results show that the COMT rs4680 (val(158)met) polymorphism is most strongly associated with outcome measures, such that individuals with the minor A allele (met) exhibit reduced COMT activity, increased TMD risk, and increased musculoskeletal pain. Epistatic interactions were observed between the COMT rs4680 polymorphism and polymorphisms in GCH1 and ESR1. Among individuals with the COMT met allele, those with 2 copies of the GCH1 rs10483639 minor G allele exhibit normalized COMT activity and increased mechanical pain thresholds. Among individuals with the COMT val allele, those with 2 copies of the ESR1 rs3020377 minor A allele exhibit reduced COMT activity, increased bodily pain, and poorer self-reported health. These data reveal that the GCH1 minor G allele confers a protective advantage among met carriers, whereas the ESR1 minor A allele is disadvantageous among val carriers. Furthermore, these data suggest that the ability to predict the downstream effects of genetic variation on COMT activity is critically important to understanding the molecular basis of chronic pain conditions.

Genetics of obsessive-compulsive disorder and related disorders

Twin and family studies support a significant genetic contribution to obsessive-compulsive disorder (OCD) and related disorders, such as chronic tic disorders, trichotillomania, skin-picking disorder, body dysmorphic disorder, and hoarding disorder. Recently, population-based studies and novel laboratory-based methods have confirmed substantial heritability in OCD. Genome-wide association studies and candidate gene association studies have provided information on specific gene variations that may be involved in the pathobiology of OCD, though a substantial portion of the genetic risk architecture remains unknown.

Age- and sex-dependence of dopamine release and capacity for recovery identified in the dorsal striatum of C57/Bl6J mice

The dorsal striatum is the main input structure of the basal ganglia and the major target area of dopaminergic projections originating in the substantia nigra pars compacta. Heavily involved in the regulation of voluntary movement and habit formation, this structure is of strong importance in Parkinson's disease, obsessive-compulsive disorder, Tourette's syndrome and addiction. The C57/Bl6J mouse strain, the most commonly used strain in preclinical research today, is frequently used as a model organism for analysis of dopaminergic parameters implicated in human pathophysiology. Several components of the dopamine system have been shown to vary with age and sex, however knowledge of the contribution of these factors for dopamine release kinetics in the C57/Bl6J mouse strain is lacking. In the present study, we used an intracranial KCl-stimulation challenge paradigm to provoke release from dopaminergic terminals in the dorsal striatum of anaesthetized C57/Bl6J mice. By high-speed in vivo chronoamperometric recordings, we analyzed DA release parameters in male and female mice of two different ages. Our experiments demonstrate elevated DA amplitudes in adult compared to young mice of both sexes and higher DA amplitudes in females compared to males at both ages. Adult mice exhibited higher recovery capabilities after repeated stimulation than did young mice and also showed a lower variability in the kinetic parameters t_rise and t₈₀ between stimulations. These results identified age- and sex- dimorphisms in DA release parameters and point to the importance of taking these dimorphisms into account when utilizing the C57/Bl6J mouse strain as model for neurological and neuropsychiatric disorders.

Animal models of obsessive-compulsive spectrum disorders

Obsessive-compulsive disorder (OCD) and related conditions (trichotillomania, pathological skin-picking, pathological nail-biting) are common and disabling. Current treatment approaches fail to help a significant proportion of patients. Multiple tiers of evidence link these conditions with underlying dysregulation of particular cortico-subcortical circuitry and monoamine systems, which represent targets for treatment. Animal models designed to capture aspects of these conditions are critical for several reasons. First, they help in furthering our understanding of neuroanatomical and neurochemical underpinnings of the obsessive-compulsive (OC) spectrum. Second, they help to account for the brain mechanisms by which existing treatments (pharmacotherapy, psychotherapy, deep brain stimulation) exert their beneficial effects on patients. Third, they inform the search for novel treatments. This article provides a critique of key animal models for selected OC spectrum disorders, beginning with initial work relating to anxiety, but moving on to recent developments in domains of genetic, pharmacological, cognitive, and ethological models. We find that there is a burgeoning literature in these areas with important ramifications, which are considered, along with salient future lines of research.

Effectiveness of paroxetine in the treatment of obsessive–compulsive disorders

Clomipramine ushered in a new age of pharmacotherapy for obsessive-compulsive disorders, and it also facilitated our understanding of the biological aspects of obsessive-compulsive disorder, focusing on the serotonergic systems. The introduction of selective serotonin reuptake inhibitors has led to great progress in the pharmacological study of obsessive-compulsive disorder based on the serotonin hypothesis. Currently, selective serotonin reuptake inhibitors are positioned as a first-line drug of obsessive-compulsive disorder pharmacotherapy in the various guidelines and algorithms. Among six different selective serotonin reuptake inhibitors (paroxetine, sertraline, fluoxetine, fluvoxamine, citalopram, escitalopram) that are available worldwide, paroxetine has the broadest treatment spectrum and promises great benefits not only for obsessive-compulsive disorder patients, but also for those with comorbid depression and/or various kinds of anxiety disorders. This paper presents several clinical trials of paroxetine carried out, and discusses and reviews the therapeutic strategies for obsessive-compulsive disorder.

Genetics of obsessive–compulsive disorder: a research update

The genetic study of obsessive-compulsive disorder (OCD) has made significant gains in the past decade. However, etiological gene findings are still elusive. Epidemiological studies, including family and twin studies, strongly support a genetic component for OCD. In addition, complex segregation analyses suggest the presence of at least one major gene. The neurobiology of OCD also lends support to the notion that programmed CNS-based biological processes underlie OCD symptom expression, with mapping of brain circuits to fronto-subcortical circuits in a consistent manner. Genetic linkage studies of OCD, using families with multiple affected relatives, have generated several suggestive linkage peaks, regions that may harbor a gene or genes for OCD. However, the presence of multiple linkage peaks has added to the complexity of OCD genetics, suggesting that the exploration of gene-gene interactions and gene-environment interactions, in addition to the exploration of alternate phenotypes based on symptom expression, age at onset or comorbid conditions, may be key in locating etiologic genes. Finally, candidate gene studies, while promising, are not yet associated with linkage regions, except in the case of the glutamate transporter gene SLC1A1 in 9p24. While OCD appears to have a genetic component, additional innovative research is needed to unravel the genetic influences in the disorder.

Relationship between the COMT-Val158Met and BDNF-Val66Met polymorphisms, childhood trauma and psychotic experiences in an adolescent general population sample

Objective

Psychotic experiences occur at a much greater prevalence in the population than psychotic disorders. There has been little research to date, however, on genetic risk for this extended psychosis phenotype. We examined whether COMT or BDNF genotypes were associated with psychotic experiences or interacted with childhood trauma in predicting psychotic experiences.

Method

Psychiatric interviews and genotyping for COMT-Val158Met and BDNF-Val66Met were carried out on two population-based samples of 237 individuals aged 11-15 years. Logistic regression was used to examine for main effects by genotype and childhood trauma, controlling for important covariates. This was then compared to a model with a term for interaction between genotype and childhood trauma. Where a possible interaction was detected, this was further explored in stratified analyses.

Results

While childhood trauma showed a borderline association with psychotic experiences, COMT-Val158Met and BDNF-Val66Met genotypes were not directly associated with psychotic experiences in the population. Testing for gene x environment interaction was borderline significant in the case of COMT-Val158Met with individuals with the COMT-Val158Met Val-Val genotype, who had been exposed to childhood trauma borderline significantly more likely to report psychotic experiences than those with Val-Met or Met-Met genotypes. There was no similar interaction by BDNF-Val66Met genotype.

Conclusion

The COMT-Val158Met Val-Val genotype may be a genetic moderator of risk for psychotic experiences in individuals exposed to childhood traumatic experiences.

Developmental imaging genetics: linking dopamine function to adolescent behavior

Adolescence is a period of development characterized by numerous neurobiological changes that significantly influence behavior and brain function. Adolescence is of particular interest due to the alarming statistics indicating that mortality rates increase two to three-fold during this time compared to childhood, due largely to a peak in risk-taking behaviors resulting from increased impulsivity and sensation seeking. Furthermore, there exists large unexplained variability in these behaviors that are in part mediated by biological factors. Recent advances in molecular genetics and functional neuroimaging have provided a unique and exciting opportunity to non-invasively study the influence of genetic factors on brain function in humans. While genes do not code for specific behaviors, they do determine the structure and function of proteins that are essential to the neuronal processes that underlie behavior. Therefore, studying the interaction of genotype with measures of brain function over development could shed light on critical time points when biologically mediated individual differences in complex behaviors emerge. Here we review animal and human literature examining the neurobiological basis of adolescent development related to dopamine neurotransmission. Dopamine is of critical importance because of (1) its role in cognitive and affective behaviors, (2) its role in the pathogenesis of major psychopathology, and (3) the protracted development of dopamine signaling pathways over adolescence. We will then focus on current research examining the role of dopamine-related genes on brain function. We propose the use of imaging genetics to examine the influence of genetically mediated dopamine variability on brain function during adolescence, keeping in mind the limitations of this approach.

Molecular genetics of obsessive-compulsive disorder: a comprehensive meta-analysis of genetic association studies

Twin studies indicate that obsessive-compulsive disorder (OCD) is strongly influenced by additive genetic factors. Yet, molecular genetic association studies have yielded inconsistent results, possibly because of differences across studies in statistical power. Meta-analysis can yield greater power. This study reports the first comprehensive meta-analysis of the relationship between OCD and all previously examined polymorphisms for which there was sufficient information in the source studies to compute odds ratios (ORs). A total of 230 polymorphisms from 113 genetic association studies were identified. A full meta-analysis was conducted for 20 polymorphisms that were examined in 5 or more data sets, and a secondary meta-analysis (limited to the computation of mean effect sizes) was conducted for 210 polymorphisms that were examined in fewer than 5 data sets. In the main meta-analysis, OCD was associated with serotonin-related polymorphisms (5-HTTLPR and HTR2A) and, in males only, with polymorphisms involved in catecholamine modulation (COMT and MAOA). Nonsignificant trends were identified for two dopamine-related polymorphisms (DAT1 and DRD3) and a glutamate-related polymorphism (rs3087879). The secondary meta-analysis identified another 18 polymorphisms with significant ORs that merit further investigation. This study demonstrates that OCD is associated with multiple genes, with most having a modest association with OCD. This suggests a polygenic model of OCD, consistent with twin studies, in which multiple genes make small, incremental contributions to the risk of developing the disorder. Future studies, with sufficient power to detect small effects, are needed to investigate the genetic basis of OCD subtypes, such as early vs late onset OCD.

Gender differences in obsessive-compulsive disorder: a literature review

INTRODUCTION

Obsessive-compulsive disorder (OCD) is a heterogeneous condition, in which subtypes have been proposed. Previous studies suggested that gender plays a relevant role in OCD phenotypic expression. This study aimed to review the literature on gender differences in clinical, genetic or familial aspects of OCD.

METHOD

A conventional review was conducted, including all papers that investigated demographic, clinical, and genetic aspects of OCD according to gender. The search was based on data available in Medline and PsycINFO databases in the last 20 years, using as keywords: obsessive-compulsive disorder; and: gender, sex, male, female, demographic characteristics, clinical features, clinical characteristics, genetic, genes, genetics gender OCD, genes OCD, genes OCD males, genes OCD females.

RESULTS

Sixty three of 487 phenotypical and genetics studies were selected. Most studies indicate that male patients are more likely than females to be single, present early onset of symptoms and chronic course of the disorder, greater social impairment, more sexual-religious and aggressive symptoms, and greater comorbidity with tic and substance use disorders. Female patients present more contamination/cleaning symptoms and greater comorbidity with eating and impulse-control disorders. Genetic and family studies are inconclusive, but suggest that gender may play a role in the disease expression.

CONCLUSIONS

Gender is a relevant factor that should be taken into account when evaluating OCD patients. More studies are necessary to determine whether in fact it defines a homogeneous and particular group in OCD.

Catechol-O-methyltranferase gene expression is associated with response to citalopram in obsessive-compulsive disorder

OBJECTIVE

To determine whether polymorphisms of the dopamine D(2) receptor (DRD2) and catechol-O-methyl-transferase (COMT) receptor genes affect the efficacy of quetiapine addition to citalopram in patients with OCD.

METHODS

Sixty-four drug-free or drug-naïve patients meeting DSM-IV criteria for OCD were randomized to 10 weeks double-blind treatment with citalopram (60 mg/day) with quetiapine (300 -450 mg/day) or with placebo. The change from baseline to endpoint on the total Yale-Brown Obsessive-Compulsive Scale (Y-BOCS) and the response to treatment were the primary outcome measures. Response was defined as a 25% decrease in Y-BOCS score. Responders and nonresponders were stratified according to DRD2 TaqI A and COMT Val(158)Met genotypes.

RESULTS

No significant differences in genotype distribution or allele frequencies of the COMT or DRD2 receptor were found between responders and nonresponders to citalopram with quetiapine. However, nearly half of responders to citalopram with placebo carried the Met/Met (48%) genotype of the COMT polymorphism compared to none of the nonresponders (χ(2) = 10.06, df = 2, P = 0.007).

CONCLUSIONS

The Met allele load of the COMT receptor gene was associated with response to 10 weeks of treatment with citalopram in drug-free or drug-naïve OCD patients.

Sex Differences in Genetic and Environmental Influences on Obsessive–Compulsive Symptoms in South Korean Adolescent and Young Adult Twins

Recent molecular genetic studies provide suggestive evidence for sexual dimorphism in genetics of obsessive-compulsive disorder. However, only a few twin studies have addressed the question of sex differences in genetic and environmental contributions to variation of obsessive–compulsive symptoms. The aim of the present study was to estimate genetic and environmental influences on obsessive–compulsive symptoms in South Korean twins, with a special emphasis on sex difference. In total, 751 adolescent and young adult twin pairs (ages: 13–23 years) completed a Korean version of the 30 items of the Maudsley Obsessional — Compulsive Inventory (MOCI) through a mail survey. A sum of the answers for the 30 items was calculated to represent a total score for obsessive–compulsive symptoms (hereafter, the MOCIT). Males had significantly higher variance of the MOCIT than did females. In males, monozygotic (MZ) twin correlation was significantly higher than dizygotic (DZ) twin correlations (.56 vs. .24), whereas in females, MZ and DZ twin correlations were not significantly different from each other (.39 vs. .36). The general sex-limitation model was applied to the twin data. The results of model-fitting analyses indicated that the unstandardized genetic variance as well as heritability estimate (53% vs. 41%) for the MOCIT was higher in males than in females. However, shared environmental influences did not attain statistical significance perhaps due to insufficient statistical power.

Serotonin-2A receptor and catechol-O-methyltransferase polymorphisms in panic disorder

Catechol-O-methyltransferase (COMT) and serotonin receptor 2A (5HTR2A) polymorphisms have been investigated for their possible role in panic disorder (PD). The aim of this study was to investigate the genotype distribution of the COMT val158met and 5HTR2A 102T/C polymorphisms in PD. COMT val158met is a polymorphism at codon 158 that results in variations in COMT enzymatic activity with high- (H) and low-activity (L) alleles. The 5HTR2A 102T/C polymorphism comprises a T-to-C mutation at position 102. The effects of symptom severity, gender, and age of onset were also investigated. The participants were 105 outpatients with PD and 130 controls. The severity of the symptoms of PD was assessed by the Panic and Agoraphobia Scale (PAS). Polymorphisms of the 5HTR2A and COMT genes were identified using polymerase chain reaction and restriction fragment length polymorphism analysis. A significant relationship was found between the COMT Val158Met polymorphism and PD. No significant differences were found in genotype distributions or allele frequencies of the 5HTR2A polymorphisms between the PD and control groups. There were no significant relationships between the COMT and 5HTR2A polymorphisms and age of onset, gender, presence of agoraphobia, or PAS scores in the PD group (p>0.05).

Association analysis of serotonin and catecholamine system candidate genes in obsessive-compulsive disorder in the Chinese population

Serotonin and catecholamine system studies provide increasing evidence for the importance of genetic factors in obsessive-compulsive disorder (OCD); we found that genetic linkage disequilibrium with OCD existed in the 5-HT2A-receptor promoter polymorphism -1438G/A. The results of our research strongly suggested that the -1438G/A promoter polymorphism plays a role in the psychopathology of OCD.

Gender effect of catechol-O-methyltransferase Val158Met polymorphism on suicidal behavior

Genetic factors and catecholaminergic dysfunction have been suggested as the etiology of suicide. The catechol-O-methyltransferase (COMT) 158Val/Met polymorphism affects COMT activity; that is, the alleles encoding Val and Met are associated with relatively high and relatively low COMT activity, respectively. We aimed to identify the role of the COMT Val158Met polymorphism in suicidal attempt behavior. The COMT 158Val/Met polymorphisms were analyzed in 197 suicide attempters (male/female: 70/127), 170 control subjects (male/female: 85/85). All subjects were ethnic Korean. The Lethality Suicide Attempt Rating Scale (LSARS) and risk-rescue rating (RRR) system were explored. For the male subjects, there was a significant difference in genotype distributions and allele frequencies between control subjects and suicide attempters. That is, Val/Val genotype and Val carriers were more frequent in suicide attempters than in control subjects. For the female subjects, however, no significant difference was shown in genotype distributions and allele frequencies between control subjects and suicide attempters. There were no significant differences in LSARS and RRR according to the genotypes. The distribution of the COMT 158Val/Met polymorphism showed a biologically meaningful difference between control subjects and suicide attempters among the male subjects although selection bias should be considered.

Comorbid obsessive-compulsive personality disorder in obsessive-compulsive disorder (OCD): a marker of severity

INTRODUCTION

Comorbid obsessive-compulsive personality disorder (OCPD) is well-described in obsessive-compulsive disorder (OCD). It remains unclear, however, whether OCPD in OCD represents a distinct subtype of OCD or whether it is simply a marker of severity in OCD.

MATERIALS AND METHODS

The aim of this study was to compare a large sample of OCD subjects (n=403) with and without OCPD on a range of demographic, clinical and genetic characteristics to evaluate whether comorbid OCPD in OCD represents a distinct subtype of OCD, or is a marker of severity.

RESULTS

Our findings suggest that OCD with and without OCPD are similar in terms of gender distribution and age at onset of OC symptoms. Compared to OCD-OCPD (n=267, 66%), those with OCD+OCPD (n=136, 34%) are more likely to present with the OC symptom dimensions which reflect the diagnostic criteria for OCPD (e.g., hoarding), and have significantly greater OCD severity, comorbidity, functional impairment, and poorer insight. Furthermore there are no differences in distribution of gene variants, or response to treatment in the two groups.

CONCLUSION

The majority of our findings suggest that in OCD, patients with OCPD do not have a highly distinctive phenomenological or genetic profile, but rather that OCPD represents a marker of severity.

Association of catechol-O-methyl transferase (COMT) gene -287A/G polymorphism with susceptibility to obsessive-compulsive disorder in Chinese Han population

Several studies suggested a genetic component in the etiology of obsessive-compulsive disorder (OCD). COMT involves in the degradation of dopamine and norepinephrin. As another functional SNP locus, COMT -287A/G polymorphism showed an effect on enzyme activity, suggesting that it may influence brain dopamine levels. To identify association of COMT -287A/G polymorphism with susceptibility to OCD in Chinese Han population. We evaluate the genetic contribution of the COMT -287A/G polymorphism in 200 OCD patients and 403 OCD-free control of Chinese Han population by PCR-RFLP. In addition, we investigate whether COMT -287A/G polymorphism is associated with one or more of these symptom dimensions or other characteristics such as sex, age of onset, and tic-relatedness and evaluate the association of the factorial structure of OCD symptoms from the Y-BOCS checklist with the COMT -287A/G polymorphism. A statistical difference was found in the genotypic frequencies of COMT -287A/G between the OCD and control groups (χ(2)  = 13.99, DF = 2, P = 0.00091) and in the genotypic frequencies of GG genotype versus AA and AG genotypes of COMT -287 (χ(2)  = 13.49, DF = 1, P = 0.00024, OR = 3.43, 95% CI = 1.78-6.62). There was a trend for an association in the genotypic distributions of COMT -287A/G polymorphism of males (χ(2)  = 27.81; DF = 2; P < 0.001) and females (χ(2)  = 7.31; DF = 2; P = 0.026) between the OCD patients and the controls. Using principal component analysis, we derived 5 factors from 12 main contents of OCD symptoms from the Y-BOCS checklist and found no association with COMT -287A/G polymorphism. Our study supports the involvement of the COMT -287A/G polymorphism in the genetic susceptibility to OCD in Chinese Han population.

Comprehensive family-based association study of the glutamate transporter gene SLC1A1 in obsessive-compulsive disorder

SLC1A1 encodes a neuronal glutamate transporter and is a promising candidate gene for obsessive-compulsive disorder (OCD). Several independent research groups have reported significant associations between OCD and single nucleotide polymorphisms (SNPs) in this gene. Previously, we evaluated 13 SNPs in, or near, SLC1A1 and reported a strong association signal with rs301443, a SNP 7.5 kb downstream of the gene [Shugart et al. (2009); Am J Med Genet Part B 150B:886–892]. The aims of the current study were first, to further investigate this finding by saturating the region around rs301443; and second, to explore the entire gene more thoroughly with a dense panel of SNP markers. We genotyped an additional 111 SNPs in or near SLC1A1, covering from 9 kb upstream to 84 kb downstream of the gene at average spacing of 1.7 kb per SNP, and conducted family-based association analyses in 1,576 participants in 377 families.We found that none of the surrounding markers were in linkage disequilibrium with rs301443, nor were any associated with OCD. We also found that SNP rs4740788, located about 8.8 kb upstream of the gene, was associated with OCD in all families (P = 0.003) and in families with male affecteds (P = 0.002). A three-SNP haplotype (rs4740788–rs10491734–rs10491733) was associated with OCD in the total sample (P = 0.00015) and in families with male affecteds (P = 0.0007). Although of nominal statistical significance considering the number of comparisons, these findings provide further support for the involvement of SLC1A1 in the pathogenesis of OCD.

Quantitative role of COMT in dopamine clearance in the prefrontal cortex of freely moving mice

Catechol-O-methyltransferase (COMT) plays an active role in the metabolism of dopamine (DA) in the prefrontal cortex (PFC). Because of low levels of dopamine transporter (DAT), it is proposed that the majority of released DA is taken up by either norepinephrine transporter (NET) and subsequently metabolized by monoamine oxidize (MAO) or by uptake(2) (to glial cells and post-synaptic neurons) and metabolized by COMT. However, a comprehensive in vivo study of rating the mechanisms involved in DA clearance in the PFC has not been done. Here, we employ two types of microdialysis to study these pathways using DAT, NET and MAO blockers in conscious mice, with or without Comt gene disruption. In quantitative no-net-flux microdialysis, DA levels were increased by 60% in the PFC of COMT-knockout (ko) mice, but not in the striatum and nucleus accumbens. In conventional microdialysis studies, we showed that selective NET and MAO inhibition increased DA levels in the PFC of wild-type mice by two- to fourfold, an effect that was still doubled in COMT-ko mice. Inhibition of DAT had no effect on DA levels in either genotype. Therefore, we conclude that in the mouse, PFC COMT contributes about one half of the total DA clearance.

The genetics of obsessive-compulsive disorder: a review

Obsessive-compulsive disorder (OCD) is a serious psychiatric disorder that affects approximately 2% of the populations of children and adults. Family aggregation studies have demonstrated that OCD is familial, and results from twin studies demonstrate that the familiality is due in part to genetic factors. Only three genome-wide linkage studies have been completed to date, with suggestive but not definitive results. In addition, over 80 candidate gene studies have been published. Most of these studies have focused on genes in the serotonergic and dopaminergic pathways. Unfortunately, none have achieved genome-wide significance, and, with the exception of the glutamate transporter gene, none have been replicated. Future research will require the collaboration of multidisciplinary teams of investigators to (i) achieve sufficiently large samples of individuals with OCD; (ii) apply the state-of-the-art laboratory techniques; and (iii) perform the bioinformatic analyses essential to the identification of risk loci.

The genetics of obsessive-compulsive disorder and Tourette syndrome: an epidemiological and pathway-based approach for gene discovery

OBJECTIVE

To provide a contemporary perspective on genetic discovery methods applied to obsessive-compulsive disorder (OCD) and Tourette syndrome (TS).

METHOD

A review of research trends in genetics research in OCD and TS is conducted, with emphasis on novel approaches.

RESULTS

Genome-wide association studies (GWAS) are now in progress in OCD and TS and will provide a platform for future discovery of common gene variants. Optimally, newer next-generation genome sequencing methods can also be used to detect larger effect genes (rare gene variants), taking advantage of pedigrees. Studies of gene networks or sets rather than individual genes will be required to elucidate biological etiology, as neural systems appear to act redundantly. Newer phenotyping strategies, such as symptom-based subtypes, cross-disorder latent class types, and intermediate phenotypes (endophenotypes) will need to be developed and tested to better align clinical and physiological measures with genetic architecture.

CONCLUSION

Although genetics research has made significant advances based on computational strength and bioinformatics advances, newer approaches to phenotyping and judicious study of gene etiological networks will be needed to uncover the genetic etiology of OCD and TS.