Genomic organization of the SLC1A1/EAAC1 gene and mutation screening in early-onset obsessive-compulsive disorder

Shared genetic loci and causal relations between schizophrenia and obsessive-compulsive disorder

Based on the clinical overlap between schizophrenia (SCZ) and obsessive-compulsive disorder (OCD), both disorders may share neurobiological substrates. In this study, we first analyzed recent large genome-wide associations studies (GWAS) on SCZ (n = 53,386, Psychiatric Genomics Consortium Wave 3) and OCD (n = 2688, the International Obsessive-Compulsive Disorder Foundation Genetics Collaborative (IOCDF-GC) and the OCD Collaborative Genetics Association Study (OCGAS)) using a conjunctional false discovery rate (FDR) approach to evaluate overlap in common genetic variants of European descent. Using a variety of biological resources, we functionally characterized the identified genomic loci. Then we used two-sample Mendelian randomization (MR) to estimate the bidirectional causal association between SCZ and OCD. Results showed that there is a positive genetic correlation between SCZ and OCD (r_g = 0.36, P = 0.02). We identified that one genetic locus (lead SNP rs5757717 in an intergenic region at CACNA1I) was jointly associated with SCZ and OCD (conjFDR = 2.12 × 10^-2). Mendelian randomization results showed that variants associated with increased risk for SCZ also increased the risk of OCD. This study broadens our understanding of the genetic architectures underpinning SCZ and OCD and suggests that the same molecular genetic processes may be responsible for shared pathophysiological and clinical characteristics between the two disorders.

Developmental impact of glutamate transporter overexpression on dopaminergic neuron activity and stereotypic behavior

Obsessive-compulsive disorder (OCD) is a disabling condition that often begins in childhood. Genetic studies in OCD have pointed to SLC1A1, which encodes the neuronal glutamate transporter EAAT3, with evidence suggesting that increased expression contributes to risk. In mice, midbrain Slc1a1 expression supports repetitive behavior in response to dopaminergic agonists, aligning with neuroimaging and pharmacologic challenge studies that have implicated the dopaminergic system in OCD. These findings suggest that Slc1a1 may contribute to compulsive behavior through altered dopaminergic transmission; however, this theory has not been mechanistically tested. To examine the developmental impact of Slc1a1 overexpression on compulsive-like behaviors, we, therefore, generated a novel mouse model to perform targeted, reversible overexpression of Slc1a1 in dopaminergic neurons. Mice with life-long overexpression of Slc1a1 showed a significant increase in amphetamine (AMPH)-induced stereotypy and hyperlocomotion. Single-unit recordings demonstrated that Slc1a1 overexpression was associated with increased firing of dopaminergic neurons. Furthermore, dLight1.1 fiber photometry showed that these behavioral abnormalities were associated with increased dorsal striatum dopamine release. In contrast, no impact of overexpression was observed on anxiety-like behaviors or SKF-38393-induced grooming. Importantly, overexpression solely in adulthood failed to recapitulate these behavioral phenotypes, suggesting that overexpression during development is necessary to generate AMPH-induced phenotypes. However, doxycycline-induced reversal of Slc1a1/EAAT3 overexpression in adulthood normalized both the increased dopaminergic firing and AMPH-induced responses. These data indicate that the pathologic effects of Slc1a1/EAAT3 overexpression on dopaminergic neurotransmission and AMPH-induced stereotyped behavior are developmentally mediated, and support normalization of EAAT3 activity as a potential treatment target for basal ganglia-mediated repetitive behaviors.

Animal Models for OCD Research

OCD has lagged behind other psychiatric illnesses in the identification of molecular treatment targets, due in part to a lack of significant findings in genome-wide association studies. However, while progress in this area is being made, OCD's symptoms of obsessions, compulsions, and anxiety can be deconstructed into distinct neural functions that can be dissected in animal models. Studies in rodents and non-human primates have highlighted the importance of cortico-basal ganglia-thalamic circuits in OCD pathophysiology, and emerging studies in human post-mortem brain tissue point to glutamatergic synapse abnormalities as a potential cellular substrate for observed dysfunctional behaviors. In addition, accumulated evidence points to a potential role for neuromodulators including serotonin and dopamine in both OCD pathology and treatment. Here, we review current efforts to use animal models for the identification of molecules, cell types, and circuits relevant to OCD pathophysiology. We start by describing features of OCD that can be modeled in animals, including circuit abnormalities and genetic findings. We then review different strategies that have been used to study OCD using animal model systems, including transgenic models, circuit manipulations, and dissection of OCD-relevant neural constructs. Finally, we discuss how these findings may ultimately help to develop new treatment strategies for OCD and other related disorders.

Early-life stress induces EAAC1 expression reduction and attention-deficit and depressive behaviors in adolescent rats

Neonatal maternal separation (NMS), as an early-life stress (ELS), is a risk factor to develop emotional disorders. However, the exact mechanisms remain to be defined. In the present study, we investigated the mechanisms involved in developing emotional disorders caused by NMS. First, we confirmed that NMS provoked impulsive behavior, orienting and nonselective attention-deficit, abnormal grooming, and depressive-like behaviors in adolescence. Excitatory amino acid carrier 1 (EAAC1) is an excitatory amino acid transporter expressed specifically by neurons and is the route for the neuronal uptake of glutamate/aspartate/cysteine. Compared with that in the normal control group, EAAC1 expression was remarkably reduced in the ventral hippocampus and cerebral cortex in the NMS group. Additionally, EAAC1 expression was reduced in parvalbumin-positive hippocampal GABAergic neurons in the NMS group. We also found that EAAC1-knockout (EAAC1-/-) mice exhibited impulsive-like, nonselective attention-deficit, and depressive-like behaviors compared with WT mice in adolescence, characteristics similar to those of the NMS behavior phenotype. Taken together, our results revealed that ELS induced a reduction in EAAC1 expression, suggesting that reduced EAAC1 expression is involved in the pathophysiology of attention-deficit and depressive behaviors in adolescence caused by NMS.

Synaptic Wiring of Corticostriatal Circuits in Basal Ganglia: Insights into the Pathogenesis of Neuropsychiatric Disorders

The striatum is a key hub in the basal ganglia for processing neural information from the sensory, motor, and limbic cortices. The massive and diverse cortical inputs entering the striatum allow the basal ganglia to perform a repertoire of neurological functions ranging from basic level of motor control to high level of cognition. The heterogeneity of the corticostriatal circuits, however, also renders the system susceptible to a repertoire of neurological diseases. Clinical and animal model studies have indicated that defective development of the corticostriatal circuits is linked to various neuropsychiatric disorders, including attention-deficit hyperactivity disorder (ADHD), Tourette syndrome, obsessive-compulsive disorder (OCD), autism spectrum disorder (ASD), and schizophrenia. Importantly, many neuropsychiatric disease-risk genes have been found to form the molecular building blocks of the circuit wiring at the synaptic level. It is therefore imperative to understand how corticostriatal connectivity is established during development. Here, we review the construction during development of these corticostriatal circuits at the synaptic level, which should provide important insights into the pathogenesis of neuropsychiatric disorders related to the basal ganglia and help the development of appropriate therapies for these diseases.

Behavioral and synaptic alterations relevant to obsessive-compulsive disorder in mice with increased EAAT3 expression

Obsessive-compulsive disorder (OCD) is a severe, chronic neuropsychiatric disorder with a strong genetic component. The SLC1A1 gene encoding the neuronal glutamate transporter EAAT3 has been proposed as a candidate gene for this disorder. Gene variants affecting SLC1A1 expression in human brain tissue have been associated with OCD. Several mouse models fully or partially lacking EAAT3 have shown no alterations in baseline anxiety-like or repetitive behaviors. We generated a transgenic mouse model (EAAT3^glo) to achieve conditional, Cre-dependent EAAT3 overexpression and evaluated the overall impact of increased EAAT3 expression at behavioral and synaptic levels. Mice with EAAT3 overexpression driven by CaMKIIα-promoter (EAAT3^glo/CMKII) displayed increased anxiety-like and repetitive behaviors that were both restored by chronic, but not acute, treatment with fluoxetine or clomipramine. EAAT3^glo/CMKII mice also displayed greater spontaneous recovery of conditioned fear. Electrophysiological and biochemical analyses at corticostriatal synapses of EAAT3^glo/CMKII mice revealed changes in NMDA receptor subunit composition and altered NMDA-dependent synaptic plasticity. By recapitulating relevant behavioral, neurophysiological, and psychopharmacological aspects, our results provide support for the glutamatergic hypothesis of OCD, particularly for the increased EAAT3 function, and provide a valuable animal model that may open novel therapeutic approaches to treat this devastating disorder.

Obsessive-compulsive symptoms in schizophrenia: a review

OBJECTIVE

To review the available literature on obsessive-compulsive symptom (OCS)/obsessive-compulsive disorder (OCD) in patients with schizophrenia.

METHODOLOGY

Electronic searches were carried out to locate studies reporting various aspects of OCS/OCD in patients with schizophrenia.

RESULTS

Available evidence suggests that prevalence of OCS/OCD in patients with schizophrenia is much higher than prevalence in general population and it is seen in all the stages of schizophrenia, starting from at risk mental state to chronic/stabilisation/deficit phases. Symptom profile of OCS/OCD in schizophrenia is similar to that seen in patients with OCD only. Presence of OCS/OCD is associated with higher severity of symptoms of schizophrenia and more negative outcome. At present there is very limited data on the efficacy/effectiveness of various pharmacological measures and psychological interventions, for management of OCS/OCD in patients with schizophrenia. There is some evidence pointing towards beneficial effect of certain antipsychotics, antidepressants and cognitive behaviour therapy. Management of OCS/OCD in patients with schizophrenia involves proper assessment. If the OCS/OCD is related to use of particular antipsychotic use, initial attempt must be made to reduce the dose of antipsychotics, however, if this is not effective, than addition of a selective serotonin reuptake inhibitor (SSRIs) must be considered. If the OCS/OCD is not related to the use of antipsychotic medication, than depending up on the severity of psychotic symptoms, addition of SSRIs must be considered.

CONCLUSION

This review suggests that OCS/OCD is highly prevalent among patients with schizophrenia and there is limited good quality evidence to make any specific recommendations for management.

OCD candidate gene SLC1A1/EAAT3 impacts basal ganglia-mediated activity and stereotypic behavior

Obsessive-compulsive disorder (OCD) is a chronic, disabling condition with inadequate treatment options that leave most patients with substantial residual symptoms. Structural, neurochemical, and behavioral findings point to a significant role for basal ganglia circuits and for the glutamate system in OCD. Genetic linkage and association studies in OCD point to SLC1A1, which encodes the neuronal glutamate/aspartate/cysteine transporter excitatory amino acid transporter 3 (EAAT3)/excitatory amino acid transporter 1 (EAAC1). However, no previous studies have investigated EAAT3 in basal ganglia circuits or in relation to OCD-related behavior. Here, we report a model of Slc1a1 loss based on an excisable STOP cassette that yields successful ablation of EAAT3 expression and function. Using amphetamine as a probe, we found that EAAT3 loss prevents expected increases in (i) locomotor activity, (ii) stereotypy, and (iii) immediate early gene induction in the dorsal striatum following amphetamine administration. Further, Slc1a1-STOP mice showed diminished grooming in an SKF-38393 challenge experiment, a pharmacologic model of OCD-like grooming behavior. This reduced grooming is accompanied by reduced dopamine D₁ receptor binding in the dorsal striatum of Slc1a1-STOP mice. Slc1a1-STOP mice also exhibit reduced extracellular dopamine concentrations in the dorsal striatum both at baseline and following amphetamine challenge. Viral-mediated restoration of Slc1a1/EAAT3 expression in the midbrain but not in the striatum results in partial rescue of amphetamine-induced locomotion and stereotypy in Slc1a1-STOP mice, consistent with an impact of EAAT3 loss on presynaptic dopaminergic function. Collectively, these findings indicate that the most consistently associated OCD candidate gene impacts basal ganglia-dependent repetitive behaviors.

Rodent models of obsessive compulsive disorder: Evaluating validity to interpret emerging neurobiology

Obsessive Compulsive Disorder (OCD) is a common neuropsychiatric disorder with unknown molecular underpinnings. Identification of genetic and non-genetic risk factors has largely been elusive, primarily because of a lack of power. In contrast, neuroimaging has consistently implicated the cortico-striatal-thalamo-cortical circuits in OCD. Pharmacological treatment studies also show specificity, with consistent response of OCD symptoms to chronic treatment with serotonin reuptake inhibitors; although most patients are left with residual impairment. In theory, animal models could provide a bridge from the neuroimaging and pharmacology data to an understanding of pathophysiology at the cellular and molecular level. Several mouse models have been proposed using genetic, immunological, pharmacological, and optogenetic tools. These experimental model systems allow testing of hypotheses about the origins of compulsive behavior. Several models have generated behavior that appears compulsive-like, particularly excessive grooming, and some have demonstrated response to chronic serotonin reuptake inhibitors, establishing both face validity and predictive validity. Construct validity is more difficult to establish in the context of a limited understanding of OCD risk factors. Our current models may help us to dissect the circuits and molecular pathways that can elicit OCD-relevant behavior in rodents. We can hope that this growing understanding, coupled with developing technology, will prepare us when robust OCD risk factors are better understood.

The importance of the excitatory amino acid transporter 3 (EAAT3)

The neuronal excitatory amino acid transporter 3 (EAAT3) is fairly ubiquitously expressed in the brain, though it does not necessarily maintain the same function everywhere. It is important in maintaining low local concentrations of glutamate, where its predominant post-synaptic localization can buffer nearby glutamate receptors and modulate excitatory neurotransmission and synaptic plasticity. It is also the main neuronal cysteine uptake system acting as the rate-limiting factor for the synthesis of glutathione, a potent antioxidant, in EAAT3 expressing neurons, while on GABAergic neurons, it is important in supplying glutamate as a precursor for GABA synthesis. Several diseases implicate EAAT3, and modulation of this transporter could prove a useful therapeutic approach. Regulation of EAAT3 could be targeted at several points for functional modulation, including the level of transcription, trafficking and direct pharmacological modulation, and indeed, compounds and experimental treatments have been identified that regulate EAAT3 function at different stages, which together with observations of EAAT3 regulation in patients is giving us insight into the endogenous function of this transporter, as well as the consequences of altered function. This review summarizes work done on elucidating the role and regulation of EAAT3.

Using mice to model Obsessive Compulsive Disorder: From genes to circuits

Obsessive Compulsive Disorder (OCD) is a severe, chronic, and highly prevalent psychiatric disorder that affects between 1.5% and 3% of people worldwide. Despite its severity, high prevalence, and clear societal cost, current OCD therapies are only partially effective. In order to ultimately develop improved treatments for this severe mental illness, we need further research to gain an improved understanding of the pathophysiology that underlies obsessions and compulsions. Though studies in OCD patients can provide some insight into the disease process, studies in humans are inherently limited in their ability to dissect pathologic processes because of their non-invasive nature. The recent development of strategies for genetic and circuit-specific manipulation in rodent models finally allows us to identify the molecular, cellular, and circuit events that lead to abnormal repetitive behaviors and affect dysregulation relevant to OCD. This review will highlight recent studies in mouse model systems that have used transgenic and optogenetic tools in combination with classic pharmacology and behavioral techniques to advance our understanding of these pathologic processes.

DISSECTING OCD CIRCUITS: FROM ANIMAL MODELS TO TARGETED TREATMENTS

Obsessive-compulsive disorder (OCD) is a chronic, severe mental illness with up to 2-3% prevalence worldwide. In fact, OCD has been classified as one of the world's 10 leading causes of illness-related disability according to the World Health Organization, largely because of the chronic nature of disabling symptoms.([1]) Despite the severity and high prevalence of this chronic and disabling disorder, there is still relatively limited understanding of its pathophysiology. However, this is now rapidly changing due to development of powerful technologies that can be used to dissect the neural circuits underlying pathologic behaviors. In this article, we describe recent technical advances that have allowed neuroscientists to start identifying the circuits underlying complex repetitive behaviors using animal model systems. In addition, we review current surgical and stimulation-based treatments for OCD that target circuit dysfunction. Finally, we discuss how findings from animal models may be applied in the clinical arena to help inform and refine targeted brain stimulation-based treatment approaches.

OCDB: a database collecting genes, miRNAs and drugs for obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a psychiatric condition characterized by intrusive and unwilling thoughts (obsessions) giving rise to anxiety. The patients feel obliged to perform a behavior (compulsions) induced by the obsessions. The World Health Organization ranks OCD as one of the 10 most disabling medical conditions. In the class of Anxiety Disorders, OCD is a pathology that shows an hereditary component. Consequently, an online resource collecting and integrating scientific discoveries and genetic evidence about OCD would be helpful to improve the current knowledge on this disorder. We have developed a manually curated database, OCD Database (OCDB), collecting the relations between candidate genes in OCD, microRNAs (miRNAs) involved in the pathophysiology of OCD and drugs used in its treatments. We have screened articles from PubMed and MEDLINE. For each gene, the bibliographic references with a brief description of the gene and the experimental conditions are shown. The database also lists the polymorphisms within genes and its chromosomal regions. OCDB data is enriched with both validated and predicted miRNA-target and drug-target information. The transcription factors regulations, which are also included, are taken from David and TransmiR. Moreover, a scoring function ranks the relevance of data in the OCDB context. The database is also integrated with the main online resources (PubMed, Entrez-gene, HGNC, dbSNP, DrugBank, miRBase, PubChem, Kegg, Disease-ontology and ChEBI). The web interface has been developed using phpMyAdmin and Bootstrap software. This allows (i) to browse data by category and (ii) to navigate in the database by searching genes, miRNAs, drugs, SNPs, regions, drug targets and articles. The data can be exported in textual format as well as the whole database in.sql or tabular format. OCDB is an essential resource to support genome-wide analysis, genetic and pharmacological studies. It also facilitates the evaluation of genetic data in OCD and the detection of alternative treatments.

Comorbid Obsessive-Compulsive Symptoms in Schizophrenia: Insight into Pathomechanisms Facilitates Treatment

Insight into the biological pathomechanism of a clinical syndrome facilitates the development of effective interventions. This paper applies this perspective to the important clinical problem of obsessive-compulsive symptoms (OCS) occurring during the lifetime diagnosis of schizophrenia. Up to 25% of schizophrenia patients suffer from OCS and about 12% fulfil the diagnostic criteria of obsessive-compulsive disorder (OCD). This is accompanied by marked subjective burden of disease, high levels of anxiety, depression and suicidality, increased neurocognitive impairment, less favourable levels of social and vocational functioning, and greater service utilization. Comorbid patients can be assigned to heterogeneous subgroups. It is assumed that second generation antipsychotics (SGAs), most importantly clozapine, might aggravate or even induce second-onset OCS. Several epidemiological and pharmacological arguments support this assumption. Specific genetic risk factors seem to dispose patients with schizophrenia to develop OCS and risk-conferring polymorphisms has been defined in SLC1A1, BDNF, DLGAP3, and GRIN2B and in interactions between these individual genes. Further research is needed with detailed characterization of large samples. In particular interactions between genetic risk constellations, pharmacological and psychosocial factors should be analysed. Results will further define homogeneous subgroups, which are in need for differential causative interventions. In clinical practise, schizophrenia patients should be carefully monitored for OCS, starting with at-risk mental states of psychosis and longitudinal follow-ups, hopefully leading to the development of multimodal therapeutic interventions.

Changes in the expression of the glutamate transporter EAAT3/EAAC1 in health and disease

Excitatory amino acid transporters (EAATs) are high-affinity Na(+)-dependent carriers of major importance in maintaining glutamate homeostasis in the central nervous system. EAAT3, the human counterpart of the rodent excitatory amino acid carrier 1 (EAAC1), is encoded by the SLC1A1 gene. EAAT3/EAAC1 is ubiquitously expressed in the brain, mostly in neurons but also in other cell types, such as oligodendrocyte precursors. While most of the glutamate released in the synapses is taken up by the "glial-type" EAATs, EAAT2 (GLT-1 in rodents) and EAAT1 (GLAST), the functional role of EAAT3/EAAC1 is related to the subtle regulation of glutamatergic transmission. Moreover, because it can also transport cysteine, EAAT3/EAAC1 is believed to be important for the synthesis of intracellular glutathione and subsequent protection from oxidative stress. In contrast to other EAATs, EAAT3/EAAC1 is mostly intracellular, and several mechanisms have been described for the rapid regulation of the membrane trafficking of the transporter. Moreover, the carrier interacts with several proteins, and this interaction modulates transport activity. Much less is known about the slow regulatory mechanisms acting on the expression of the transporter, although several recent reports have identified changes in EAAT3/EAAC1 protein level and activity related to modulation of its expression at the gene level. Moreover, EAAT3/EAAC1 expression is altered in pathological conditions, such as hypoxia/ischemia, multiple sclerosis, schizophrenia, and epilepsy. This review summarizes these results and provides an overall picture of changes in EAAT3/EAAC1 expression in health and disease.

Comorbid obsessive-compulsive symptoms in schizophrenia: contributions of pharmacological and genetic factors

A large subgroup of around 25% of schizophrenia patients suffers from obsessive-compulsive symptoms (OCS) and about 12% fulfill the diagnostic criteria of an obsessive-compulsive disorder (OCD). The additional occurrence of OCS is associated with high subjective burden of disease, additional neurocognitive impairment, poorer social and vocational functioning, greater service utilization and high levels of anxiety and depression. Comorbid patients can be assigned to heterogeneous subgroups. One hypothesis assumes that second generation antipsychotics (SGAs), most importantly clozapine, might aggravate or even induce second-onset OCS. Several arguments support this assumption, most importantly the observed chronological order of first psychotic manifestation, start of treatment with clozapine and onset of OCS. In addition, correlations between OCS-severity and dose and serum levels and duration of clozapine treatment hint toward a dose-dependent side effect. It has been hypothesized that genetic risk-factors dispose patients with schizophrenia to develop OCS. One study in a South Korean sample reported associations with polymorphisms in the gene SLC1A1 (solute carrier family 1A1) and SGA-induced OCS. However, this finding could not be replicated in European patients. Preliminary results also suggest an involvement of polymorphisms in the BDNF gene (brain-derived neurotrophic factor) and an interaction between markers of SLC1A1 and the gene DLGAP3 (disc large associated protein 3) as well as GRIN2B (N-methyl-D-aspartate receptor subunit 2B). Further research of well-defined samples, in particular studies investigating possible interactions of genetic risk-constellations and pharmacodynamic properties, are needed to clarify the assumed development of SGA-induced OCS. Results might improve pathogenic concepts and facilitate the definition of at risk populations, early detection and monitoring of OCS as well as multimodal therapeutic interventions.

Meta-analysis of association between obsessive-compulsive disorder and the 3' region of neuronal glutamate transporter gene SLC1A1

The neuronal glutamate transporter gene SLC1A1 is a candidate gene for obsessive-compulsive disorder (OCD) based on linkage studies and convergent evidence implicating glutamate in OCD etiology. The 3' end of SLC1A1 is the only genomic region with consistently demonstrated OCD association, especially when analyzing male-only probands. However, specific allele associations have not been consistently replicated, and recent OCD genome-wide association and meta-analysis studies have not incorporated all previously associated SLC1A1 SNPs. To clarify the nature of association between SLC1A1 and OCD, pooled analysis was performed on all available relevant raw study data, comprising a final sample of 815 trios, 306 cases and 634 controls. This revealed weak association between OCD and one of nine tested SLC1A1 polymorphisms (rs301443; uncorrected P = 0.046; non-significant corrected P). Secondary analyses of male-affecteds only (N = 358 trios and 133 cases) demonstrated modest association between OCD and a different SNP (rs12682807; uncorrected P = 0.012; non-significant corrected P). Findings of this meta-analysis are consistent with the trend of previous candidate gene studies in psychiatry and do not clarify the putative role of SLC1A1 in OCD pathophysiology. Nonetheless, it may be important to further examine the potential associations demonstrated in this amalgamated sample, especially since the SNPs with modest associations were not included in the more highly powered recent GWAS or in a past meta-analysis including five SLC1A1 polymorphisms. This study underscores the need for much larger sample sizes in future genetic association studies and suggests that next-generation sequencing may be beneficial in examining the potential role of rare variants in OCD.

Functional studies and rare variant screening of SLC1A1/EAAC1 in males with obsessive-compulsive disorder

Several studies have found that the neuronal glutamate transporter gene SLC1A1/EAAC1 is associated with obsessive-compulsive disorder (OCD), with a stronger association in males. Previous studies have primarily focused on common single-nucleotide polymorphisms, rather than rare functional variants that are likely to have larger effects. We screened 184 males with OCD for rare variation in SLC1A1 exons; however, no new coding variation was found. When combined with previous screens, only one SLC1A1 amino acid variant has been detected among the 841 individuals screened, which is less than for other neurotransmitter transporter genes (P=0.0001). We characterized the function of the one SLC1A1 missense variant reported previously in OCD, Thr164Ala, and found that the Ala164 allele leads to decreased Vmax and Km (P<0.0001) in transfected human embryonic kidney cells. Further work will be necessary to understand the impact of this rare SLC1A1/EAAC1 Ala164 variant on neuronal function and circuitry relevant to OCD.

Polymorphisms in the glutamate transporter gene SLC1A1 and obsessive-compulsive symptoms induced by second-generation antipsychotic agents

BACKGROUND

A large subgroup of schizophrenic patients develops obsessive-compulsive symptoms (OCS) during treatment with second-generation antipsychotics (SGA). A genetic risk factor for these secondary OCS was recently described in the gene SLC1A1 encoding the neuronal glutamate transporter excitatory amino acid carrier 1. The aim of this study was to replicate these findings in a European sample.

METHODS

A total of 103 schizophrenic patients treated with SGAs were included. Three single nucleotide polymorphisms in SLC1A1 (rs2228622, rs3780412 and rs3780413), which had been associated with SGA-induced OCS, were investigated. Single marker and haplotype analyses were tested with logistic regressions using age, sex and medication type as covariates.

RESULTS

Treatment with markedly antiserotonergic SGAs such as clozapine was more prevalent in the subgroup of patients with comorbid OCS (P<0.001). The dosage and duration of clozapine treatment correlated significantly with the severity of OCS. In contrast to the Asian sample, no genetic associations were found with OCS.

CONCLUSION

Larger samples are necessary to unravel the interplay of pharmacological and genetic risk factors for OCS in schizophrenia.

Clozapine-induced obsessive-compulsive symptoms in schizophrenia: a critical review

Obsessive-compulsive disorder (OCD) is rarely associated with schizophrenia, whereas 20 to 30% of schizophrenic patients, suffer from comorbid obsessive-compulsive symptoms (OCS). So far no single pathogenetic theory convincingly explained this fact suggesting heterogeneous subgroups. Based on long-term case observations, one hypothesis assumes that second-onset OCS in the course of schizophrenia might be a side effect of second generation antipsychotics (SGA), most importantly clozapine (CLZ). This review summarizes the supporting epidemiological and pharmacological evidence: Estimations on prevalence of OCS increase in more recent cross-sectional studies and in later disease stages. Longitudinal observations report the de novo-onset of OCS under clozapine treatment. This association has not been reported with first generation antipsychotics (FGA) or SGAs with mainly dopaminergic mode of action. Finally, significant correlations of OCS-severity with duration of treatment, dose and serum levels suggest clozapine-induced OCS. However, supposed causal interactions need further verifications. It is also unclear, which neurobiological mechanisms might underlie the pathogenetic process. Detailed genotypic and phenotypic characterizations of schizophrenics with comorbid OCS regarding neurocognitive functioning and activation in sensitive tasks of functional magnetic imaging are needed. Multimodal large-scaled prospective studies are necessary to define patients at risk for second-onset OCS and to improve early detection and therapeutic interventions.

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.

Analysis of 9p24 and 11p12-13 regions in autism spectrum disorders: rs1340513 in the JMJD2C gene is associated with ASDs in Finnish sample

OBJECTIVE

Autism spectrum disorders (ASD) often show obsessive repetitive symptoms that are characteristic to obsessive-compulsive disorder (OCD). Aberrant glutamate function has been suggested to a risk for both ASDs and OCD. Considering the common metabolic pathway and recent results from association studies both in OCD and ASDs, a question, whether there is common molecular background in ASDs and OCD, was raised.

METHODS

Ten single nucleotide polymorphisms (SNPs) at 9p24 and 11p12-p13 containing glutamate transporter genes SLC1A1 and SLC1A2 and their neighboring regions in 175 patients with ASDs and 216 controls of Finnish origin were analyzed using real-time-PCR or direct sequencing.

RESULTS

The strongest association was detected with rs1340513 in the JMJD2C gene at 9p24.1 (P=0.007; corrected P=0.011) that is the same SNP associated with infantile autism (P=0.0007) in the autism genome project consortium (2007). No association was detected at 11p12-p13 with ASD. Interestingly, the strongest association in OCD has been found at rs301443 (P=0.000067) residing between SLC1A1 and JMJD2C at 9p24.

CONCLUSION

In summary, our results give evidence for a possible common locus for OCD and ASDs at 9p24. We speculate that the area may represent a special candidate region for obsessive repetitive symptoms in ASDs.

The Genetics of Obsessive-Compulsive Disorder

OCD is a psychiatric disorder with a lifetime prevalence of 1-3% and is a significant cause of disability worldwide. Family studies indicate that OCD has a significant hereditable component, with relatives of OCD cases being 4 times more likely to develop the disorder than the general population. Linkage studies in OCD have generally been underpowered and have failed to reach the statistical threshold for genome-wide significance, but they have nevertheless been useful for revealing potential regions of interest for future candidate gene studies. Candidate gene studies in OCD have thus far focused on genes involved in the serotonergic, dopaminergic, and glutamatergic pathways. These studies have been for the most part inconclusive, and failures to replicate have been the norm until very recently. The only genetic association replicated by multiple groups was with a glutamate transporter gene (SLC1A1). Genome-wide association studies in OCD are in progress, but final results have not yet been reported. As with the study of many other psychiatric disorders, an improved understanding of OCD will only be achieved (1) with larger collaborative efforts involving more probands, (2) the use of probands and controls drawn from epidemiologically-based populations rather than clinical samples, (3) developing a more precise phenotypic description of OCD and (4) measuring important environmental influences that affect OCD pathogenesis and severity.

Genome-wide linkage using the Social Responsiveness Scale in Utah autism pedigrees

BACKGROUND

Autism Spectrum Disorders (ASD) are phenotypically heterogeneous, characterized by impairments in the development of communication and social behaviour and the presence of repetitive behaviour and restricted interests. Dissecting the genetic complexity of ASD may require phenotypic data reflecting more detail than is offered by a categorical clinical diagnosis. Such data are available from the Social Responsiveness Scale (SRS) which is a continuous, quantitative measure of social ability giving scores that range from significant impairment to above average ability.

METHODS

We present genome-wide results for 64 multiplex and extended families ranging from two to nine generations. SRS scores were available from 518 genotyped pedigree subjects, including affected and unaffected relatives. Genotypes from the Illumina 6 k single nucleotide polymorphism panel were provided by the Center for Inherited Disease Research. Quantitative and qualitative analyses were done using MCLINK, a software package that uses Markov chain Monte Carlo (MCMC) methods to perform multilocus linkage analysis on large extended pedigrees.

RESULTS

When analysed as a qualitative trait, linkage occurred in the same locations as in our previous affected-only genome scan of these families, with findings on chromosomes 7q31.1-q32.3 [heterogeneity logarithm of the odds (HLOD) = 2.91], 15q13.3 (HLOD = 3.64), and 13q12.3 (HLOD = 2.23). Additional positive qualitative results were seen on chromosomes 6 and 10 in regions that may be of interest for other neuropsychiatric disorders. When analysed as a quantitative trait, results replicated a peak found in an independent sample using quantitative SRS scores on chromosome 11p15.1-p15.4 (HLOD = 2.77). Additional positive quantitative results were seen on chromosomes 7, 9, and 19.

CONCLUSIONS

The SRS linkage peaks reported here substantially overlap with peaks found in our previous affected-only genome scan of clinical diagnosis. In addition, we replicated a previous SRS peak in an independent sample. These results suggest the SRS is a robust and useful phenotype measure for genetic linkage studies of ASD. Finally, analyses of SRS scores revealed linkage peaks overlapping with evidence from other studies of neuropsychiatric diseases. The information available from the SRS itself may, therefore, reveal locations for autism susceptibility genes that would not otherwise be detected.

A screen of SLC1A1 for OCD-related alleles

SLC1A1, which encodes the neuronal and epithelial glutamate transporter, is a promising candidate gene for obsessive-compulsive disorder (OCD). In this study, we conducted capillary electrophoresis single-strand conformation polymorphism (CE-SSCP) screen for all 12 identified exons, including all coding regions and approximately 50 bp of flanking introns of the human SLC1A1 in 378 OCD-affected individuals. Full sequencing was completed on samples that showed an aberrant SSCP tracing for identification of the underlying sequence variants. Our aim was to determine if there are differences in the frequencies of relatively common alleles, or rare functional alleles, in 378 OCD cases and 281 ethnically matched controls. We identified one nonsynonymous coding SNP (c.490A > G, T164A) and three synonymous coding SNP (c.81G > C, A27A; c.414A > G, T138T; c.1110T > C, T370T) in case samples. We found no statistical differences in genotype and allele frequencies of common cSNPs in SLC1A1 between the OCD cases and controls. The rare variant T164A was found only in one family. Further investigation of this variant is necessary to determine whether and how it is related to OCD. There was no other evidence of significant accumulation of deleterious coding mutations in SLC1A1 in the OCD cases.

Genetics of early-onset obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is characterized by recurrent, intrusive and disturbing thoughts as well as by repetitive stereotypic behaviors. Epidemiological data are similar in children and adults, i.e., between 1 and 3% of the general population suffer from OCD. Children with OCD are often seriously impaired in their development. OCD, especially of early onset, has been shown to be familial. Several candidate genes of predominantly neurotransmitter systems have been analyzed and a total of three genome-wide linkage scans have been performed until now. Analyses of candidate genes in linkage regions have not provided evidence for their involvement in OCD, with the exception of the glutamate transporter gene SLC1A1 on 9p24. Genome-wide association analyses are in progress and the results will promote further independent replication studies. The consideration of subtypes regarding age of onset, symptom dimensions and/or comorbid disorders is needed.

A family-based association study of the glutamate transporter gene SLC1A1 in obsessive-compulsive disorder in 378 families

SLC1A encodes the neuronal and epithelial glutamate transporter and was previously tested as a candidate for obsessive-compulsive disorder (OCD) by several research groups. Recently, three independent research groups reported significant association findings between OCD and several genetic variants in SLC1A1. This study reports the results from a family-based association study, which examined the association between 13 single nucleotide polymorphisms (SNPs) within or in proximity to the SLC1A1 gene. Although we did not replicate association findings for those significant SNPs reported by previous studies, our study indicated a strong association signal with the SNP RS301443 (P-value = 0.000067; Bonferroni corrected P-value = 0.0167) under a dominant model, with an estimated odds ratio of 3.5 (confidence interval: 2.66-4.50). Further, we conducted single SNP analysis after stratifying the full data set by the gender status of affected in each family. The P-value for RS301443 in families with the male affected was 0.00027, and the P-value in families with female affected was 0.076. The fact that we identified a signal which was not previously reported by the other research groups may be due to differences in study designs and sample ascertainment. However, it is also possible that this significant SNP may be part of a regulator for SLC1A1, given that it is roughly 7.5 kb away from the boundary of the SLC1A1 gene. However, this potential finding needs to be validated biologically. Further functional studies in this region are planned by this research group.

A haplotype containing quantitative trait loci for SLC1A1 gene expression and its association with obsessive-compulsive disorder

CONTEXT

Recent evidence from linkage analyses and follow-up candidate gene studies supports the involvement of SLC1A1, which encodes the neuronal glutamate transporter, in the development of obsessive-compulsive disorder (OCD).

OBJECTIVES

To determine the role of genetic variation of SLC1A1 in OCD in a large case-control study and to better understand how SLC1A1 variation affects functionality.

DESIGN

A case-control study.

SETTING

Publicly accessible SLC1A1 expression and genotype data.

PATIENTS

Three hundred twenty-five OCD probands and 662 ethnically and sex-matched controls.

INTERVENTIONS

Probands were assessed with the Structured Clinical Interview for DSM-IV, the Yale-Brown Obsessive Compulsive Scale, and the Saving Inventory-Revised. Six single-nucleotide polymorphisms (SNPs) were genotyped. Multiple testing corrections for single-marker and haplotype analyses were performed by permutation.

RESULTS

Gene expression of SLC1A1 is heritable in lymphoblastoid cell lines. We identified 3 SNPs in or near SLC1A1 that correlated with gene expression levels, 1 of which had previously been associated with OCD. Two of these SNPs also predicted expression levels in human brain tissue, and 1 SNP was further functional in reporter gene studies. Two haplotypes at 3 SNPs, rs3087879, rs301430, and rs7858819, were significantly associated with OCD after multiple-testing correction and contained 2 SNPs associated with expression levels. In addition, another SNP correlating with SLC1A1 gene expression, rs3933331, was associated with an OCD-hoarding subphenotype as assessed by 2 independent, validated scales.

CONCLUSIONS

Our case-control data corroborate previous smaller family-based studies that indicated that SLC1A1 is a susceptibility locus for OCD. The expression and genotype database-mining approach we used provides a potentially useful complementary approach to strengthen future candidate gene studies in neuropsychiatric and other disorders.

Does parental expressed emotion moderate genetic effects in ADHD? An exploration using a genome wide association scan

Studies of gene x environment (G x E) interaction in ADHD have previously focused on known risk genes for ADHD and environmentally mediated biological risk. Here we use G x E analysis in the context of a genome-wide association scan to identify novel genes whose effects on ADHD symptoms and comorbid conduct disorder are moderated by high maternal expressed emotion (EE). SNPs (600,000) were genotyped in 958 ADHD proband-parent trios. After applying data cleaning procedures we examined 429,981 autosomal SNPs in 909 family trios. ADHD symptom severity and comorbid conduct disorder was measured using the Parental Account of Childhood Symptoms interview. Maternal criticism and warmth (i.e., EE) were coded by independent observers on comments made during the interview. No G x E interactions reached genome-wide significance. Nominal effects were found both with and without genetic main effects. For those with genetic main effects 36 uncorrected interaction P-values were <10(-5) implicating both novel genes as well as some previously supported candidates. These were found equally often for all of the interactions being investigated. The observed interactions in SLC1A1 and NRG3 SNPs represent reasonable candidate genes for further investigation given their previous association with several psychiatric illnesses. We find evidence for the role of EE in moderating the effects of genes on ADHD severity and comorbid conduct disorder, implicating both novel and established candidates. These findings need replicating in larger independent samples.

Evidence for a heritable unidimensional symptom factor underlying obsessionality

The division of obsessive-compulsive symptoms (OCS) into specific factors is now widely accepted. However, the utility of these categories for genetic studies remains unclear, as studies examining their heritability have been inconsistent. Less attention has been paid to the possibility that clinically significant obsessionality is primarily determined by a "core" group of OCS that crosses the boundaries between symptom subgroups. The aim of this study is to determine whether such a core group exists, and to compare its heritability to that of the more traditionally derived symptom factors. We examined the properties and heritability of obsessive-compulsive symptoms in college students, medical students, and obsessive-compulsive disorder (OCD) families using the Leyton Obsessional Inventory. In each of the three samples, we identified a core group of symptoms that comprised a single unique construct and accounted for over 90% of the variation of the four more traditional symptom factors. This core construct was highly correlated with OCD in our families and had a heritability estimate of 0.19 when OCD was not included as a covariate and 0.49 when OCD was included as a covariate. In contrast, the four symptom factors were not heritable. There appears to be an underlying unidimensional component to obsessionality, both in non-clinical and clinical samples. This component, which is heritable, accounts for the majority of the variation of the more traditionally derived symptom factors in our sample, and is composed of OCS that are not specific to any of the symptom subgroups.

Renner T, Wewetzer C, Warnke A. Genetische Befunde bei Zwangsstörungen im Kindes- und Jugendalter und bei Erwachsenen

Zusammenfassung: Im Kindes- und Jugendalter sind Zwangsstörungen bei einer Inzidenz von ein bis zwei Prozent keine Seltenheit und können die Betroffenen in ihrer Entwicklung deutlich beeinträchtigen. Die Erkrankung ist durch wiederkehrende und anhaltende Verhaltensweisen, Gedanken und Impulse gekennzeichnet, die als quälend erlebt werden und sich je nach Entwicklungstand gegen inneren Widerstand aufdrängen und vom Patienten als unsinnig und übertrieben wahrgenommen werden. Die Entstehung von Zwangsstörungen hängt sowohl von Umweltfaktoren, nicht genetischen hirnpathologischen als auch von genetischen Einflussfaktoren ab. Die Mehrheit der bisherigen Ergebnisse bezieht sich dabei auf Untersuchungen im Erwachsenenalter. Es wird eine aktuelle Übersicht über genetische Befunde bei Zwangsstörungen unter besonderer Berücksichtigung des Kindes- und Jugendalters gegeben. Bei jung erkrankten Patienten findet sich eine deutlichere familiäre Belastung. Befunde aus Kopplungs- und Assoziationsstudien sowie Tiermodellen werden vorgestellt und diskutiert. Die phänotypische und genetische Heterogenität von Zwangsstörungen trägt zu den unterschiedlichen Studienergebnissen bei und erfordert für künftige Untersuchungen die Differenzierung von Subtypen, z.B. die Einbeziehung des Alters bei Erkrankungsbeginn, von Symptomdimensionen, geschlechtlichen Besonderheiten und komorbider Störungen.

Glutamatergic Synaptic Dysfunction and Obsessive-Compulsive Disorder

Obsessive-compulsive disorder (OCD) is a debilitating neuropsychiatric condition estimated to afflict 1-3% of the world population. The estimated financial impact in the treatment and management of OCD is in the billions of dollars annually in the US alone. At present there is a marked lack of evidence on the specific causes of OCD. Current hypotheses largely focus on the serotonin (5-HT) system on the basis of the effectiveness of selective serotonin reuptake inhibitors (SSRIs) in alleviating symptoms of patients with OCD, yet a considerable fraction of patients are non-responsive or minimally responsive to these agents. Despite this fact, SSRIs have remained the primary pharmacological treatment avenue for OCD. In recent years, multiple lines of evidence have implicated glutamatergic synaptic dysfunction within the cortico-striatal-thalamo-cortical (CSTC) brain circuit in the etiology of OCD and related disorders, thereby prompting intensified effort in the development and evaluation of agents that modulate glutamatergic neurotransmission for the treatment of OCD. With this in mind, here we review the following topics with respect to synaptic dysfunction and the neural circuitry underlying OCD: (1) evidence supporting the critical involvement of the CSTC circuit, (2) genetic studies supporting the involvement of glutamatergic dysfunction, (3) insights from genetic animal models of OCD, and (4) preliminary findings with glutamatergic neurotransmission-modulating agents in the treatment of OCD. Given the putative mechanistic overlap between OCD and the broader OC-spectrum of disorders, unraveling the synaptic basis of OCD has potential to translate into more effective treatments for an array of poorly understood human disorders.

Evidence for a susceptibility locus on chromosome 10p15 in early-onset obsessive-compulsive disorder

BACKGROUND

The goal of this study was to identify chromosomal regions likely to contain susceptibility loci for obsessive-compulsive disorder (OCD).

METHODS

We conducted a genome-wide linkage scan, with average marker spacing less than 10 centimorgans (cM), in 121 subjects from 26 families ascertained through probands with early-onset OCD. Best estimate lifetime psychiatric diagnoses were based on semistructured interviews and all other available sources of information. Parametric and nonparametric linkage analyses were conducted with GENEHUNTER+ and Allegro. Family-based association analyses were done using 35 single nucleotide polymorphisms (SNPs) in the 10p15 region.

RESULTS

The maximum nonparametric log of odds (NLOD) score was 2.43 on chromosome 10p15 at position 4.37. When data from our first genome scan were added to data from this scan, the maximum NLOD score in the 10p15 region was 1.79. Association was detected on 10p15 with three adjacent SNPs, including the amino acid variant rs2271275 in the 3' region of adenosine deaminase acting on RNA 3 (ADAR3) (p < .05).

CONCLUSIONS

The results provide suggestive evidence for linkage on chromosome 10p15. Evidence for association in the linkage region was found with three markers in the 3' end of ADAR3. Limitations include the lack of significant linkage and association findings when corrected for multiple testing.

Glutamate‐dependent transcriptional regulation of GLAST/EAAT1: a role for YY1

Glutamate is the major excitatory transmitter in the vertebrate brain and its extracellular levels are tightly regulated to prevent excitotoxic effects. The Na(+)-dependent glutamate/aspartate transporter GLAST/EAAT1 is regulated in the short and in the long term by glutamate. A receptors-independent change in its membrane translocation rate, accounts for an acute modulation in GLAST/EAAT1 transport. In contrast, activation of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate subtype of glutamate receptors represses the transcription of the chick glast gene. A glutamate responsive element has been mapped to the promoter region of this gene containing a bonafide binding site for the transcription factor Ying-Yang 1. Using cultured chick cerebellar Bergmann glia cells, glutamate elicited a time and dose-dependent increase in Ying-Yang 1 DNA binding consistent with the negative response generated in a reporter gene construct controlled for Ying-Yang 1. Over-expression of this transcription factor leads to a substantial reduction in GLAST/EAAT1 transporter uptake and an important decrease in mRNA levels, all associated with the transcriptional repression of the chick glast promoter activity. These results provide evidence for an involvement of Ying-Yang 1 in the transcriptional response to glutamate in glial cells and favor the notion of a relevant role of this factor in GLAST/EAAT1 transcriptional control.

Association studies of serotonin system candidate genes in early-onset obsessive-compulsive disorder

BACKGROUND

Family-based evidence for association at serotonin system genes SLC6A4, HTR1B, HTR2A, and brain-derived neurotrophic factor (BDNF) has been previously reported in obsessive-compulsive disorder (OCD). Early-onset OCD is a more familial form of the disorder.

METHODS

We used the transmission-disequilibrium test of association at common polymorphisms in each of these genes in 54 parent-child trios ascertained through probands with early-onset OCD.

RESULTS

No evidence for association was detected at any of the polymorphisms in the entire set of subjects. Nominally significant association was found at the HTR2A rs6311 polymorphism in subjects with tic disorder and OCD (p = .05), replicating a previous finding in Tourette syndrome and OCD. Nominally significant association was also found for the SLC6A4 HT transporter gene-linked polymorphic region (5-HTTLPR) polymorphism for female subjects (p = .03). Neither association would remain significant after statistical correction for multiple testing. Despite no individual study reporting replication, a pooled analysis of five replication studies of the SLC6A4 5-HTTLPR polymorphism supports association (p = .02).

CONCLUSIONS

Low power across individual association studies in OCD may lead to a false acceptance of the null hypothesis. Accumulation of evidence from multiple studies will be necessary to evaluate the potential role for these genes in contributing to susceptibility to OCD.

What is the optimal way to subdivide obsessive-compulsive disorder?

The clinical presentation of obsessive-compulsive disorder (OCD) varies not only across patients but over the course of the disorder. This diversity indicates that OCD is a heterogeneous disorder, which may have an important impact on psychopathological, longitudinal, genetic, and treatment research. To better understand OCD heterogeneity, more homogeneous phenotypic descriptions are necessary to delimiting clinically meaningful subgroups of patients. Besides phenotypic descriptions, another method of delimiting OCD patient subgroups includes the search for endophenotypes (extended phenotypes) based on neurophysiological, immunological, genetic, neuropsychological, or neuroanatomic (neuroimaging) paradigms. This article will describe some strategies that deal with OCD heterogeneity, including the identification of more homogeneous phenotypical categories, an improved understanding of obsessive-compulsive symptom dimensions and how to use them as quantitative traits, and broadening the diagnostic boundaries of OCD to include other related conditions. The relevance and limitations of each approach are also discussed. Since the etiological mechanisms associated with the expressions of OCD are unknown, there is probably not one but several heuristic strategies to search for more homogeneous OCD subgroup, that combined may provide the most fruitful results.

The current status of association studies in obsessive-compulsive disorder

During the last 2 decades, a large number of association studies have been dedicated to disentangling the genetic components that may be involved in the etiology of OCD. The preliminary and frequently in consistent nature of the data represented in the majority of OCD psychiatric genetic-association studies may seem discouraging. Failure to replicate, and thus to confirm, previously identified susceptibility loci could result from a number of reasons, including the potential for population admixture, the clinical heterogeneity of OCD, small sample sizes (and subsequent lack of power),publication bias, epistasis, or failure to account for multiple testing. Various methods of accounting for these confounders do exist and should be implemented in any genetic-association study that is to be regarded as robust and replicable. Discrepancy between results, however, might be ascribed to the underlying genetic differences between the populations in the respective studies (ie, the investigated variant may be in linkage disequilibrium with the causal variant in one population but not in another). Such discrepancies are difficult to reconcile in single-locus association studies; haplotype analyses(in which a number of variants, usually single-nucleotide polymorphisms occurring on the same gene, are analyzed as a unit) may be able to resolve these uncertainties. Investigating epistatic interactions between variants in other genes that might be involved in the same physiologic pathways would be an alternative means of deciphering the reason for discrepant genetic association results.A valid means of increasing the power (by reducing background noise)would be to stratify the patient sample according to clinically defined sub-types, such as obsession and compulsion subtypes, age at onset of the disorder, and severity of the disorder. Although many of the OCD genetics studies have incorporated investigations of these subtypes [65,66,68,77,84-86,89,107,118,132,133,145,148,149], the number of subjects decreases after stratification, thereby limiting the power of the studies. It may therefore be useful to employ other quantitative approaches in the design of the investigation: the possibility should be considered that OCD symptoms can be broken down into multiple dimensions that are continuous with the normal population [150]. This division would represent an important route to disentangling the complex inheritance of OCD. The results obtained from genetic investigations should be incorporated with clinical and epidemiologic parameters to elucidate correctly the cause of OCD. Future studies should also be extended to incorporate the screening of more polymorphisms, because high-resolution mapping within specific chromosomes will improve knowledge regarding the impact of genetic diversity within the genes or linked chromosomal regions in OCD. The advantages ofa gene-based over a single-nucleotide polymorphism based approach are becoming ever more apparent [151]. Therefore, a more complete assessment of candidate genes, possibly using haplotype blocks that span larger regions,is proposed. In addition, increasing the amount of information on human genome sequences and polymorphisms will make it possible to characterize the amount of sequence variation expressed in the brain and to delineate the potential effects that these variations may have on the development of OCD. Knowledge of new functional variants will emerge as researchers gain an understanding of the potential for genetic variants in the coding and regulatory regions to impact gene expression.

Haplotyping by capillary electrophoresis

The investigation of the genetic background and phenotype structures of complex diseases, such as cardiovascular or psychiatric disorders and tumors, is one of the most scrutinized fields of the post genomic era. Besides the multiplex analysis of genetic markers and polymorphisms throughout the whole genome, more and more attention is focused on the interaction between the etiological factors of these traits. Haplotype determination, rather than multiplex genotyping seems to be one of the first building blocks of this endeavor. This review focuses on the importance and theoretical background of haplotyping, and summarizes the recent examples of novel and emerging haplotyping techniques by capillary gel electrophoresis based DNA fragment analysis, a powerful tool for the examination of the inheritance of complex traits.

Obsessive-compulsive disorder phenotypes: implications for genetic studies

Obsessive-compulsive disorder (OCD) clinical presentation is remarkably diverse, and can vary both within and across patients over time. This variability in the phenotypic expression has led to the hypothesis that OCD is a heterogeneous disorder and that this heterogeneity obscures the findings of clinical, natural history and treatment response studies and complicates the search for vulnerability genes. A complete understanding of what comprises OCD and the underlying etiological mechanisms will require a dramatic change in how the disorder is conceptualized. In this review, several different approaches that may represent the first steps in this reconceptualization are discussed. These approaches include (1) narrowing the phenotype to identify categorically defined more homogeneous and mutually exclusive subtypes of OCD, (2) considering OC symptom dimensions as quantitative components of the more complex OCD phenotype and (3) broadening the phenotype to include other etiologically related conditions. A combined dimensional approach within distinctive subgroups is proposed as probably the most effective in helping to identify the heritable components of OCD. By identifying heritable components of OCD, it should be possible to find genes for these separate components. The review continues with the illustration of the possible role of some epigenetic risk and protective factors in the OCD presentation and the relevance of examining associated traits and/or endophenotypes to enhance our ability to understand the genetic basis of OCD. To conclude, we discuss the variability in treatment outcome and the significance of the development of specific pharmacological and/or behavioral based therapies tailored to each of these phenotypes.

A simple, bead-based approach for multi-SNP molecular haplotyping

Single nucleotide polymorphisms (SNPs) within a gene region have often been studied to determine their effect on phenotype. Although a single base pair change can produce a phenotypic change, phenotype is often influenced by the presence of multiple polymorphisms and their relative positions within a given region. For example, if multiple changes occur in a promoter region, how they influence gene expression will depend on their cis/trans configuration. As such, it is essential to consider the haplotype, or the alignment of multiple SNP alleles on each chromosome when attempting to associate genomic changes with phenotype. Unfortunately, no method of high-throughput molecular haplotyping of multiple SNPs currently exists. In response to this unmet need, we have developed an inexpensive, reliable bead-based capture-based haplotyping (CBH) assay to determine the phase, or haplotype, of multiple SNP alleles in a high-throughput manner. The CBH assay requires minimal setup and handling, requires no centrifugation steps and can be performed in <1 h. Data collection is performed via flow cytometry and the assay yields plus/minus results allowing for automated calling by a simple computer application. We will present data demonstrating the molecular haplotyping of 11 SNPs within exon 2 of the N-acetyltransferase-2 (NAT2) gene, which expresses an important drug-metabolizing enzyme. This assay has applications in diagnostic testing, promoter analysis, association studies and pharmacogenetic analysis.

Structural factors determining DNA length limitations in conformation-sensitive mutation detection methods

Numerous mutations and polymorphisms in human genes remain to be identified using reliable methods. Of the available mutation scanning methods those dependent on structural change-induced mobility shifts are highly effective. Their efficiency is, however, DNA length-sensitive and the reasons for that are poorly understood. In this study, we explain why scanning genes for mutations is less effective in longer DNA fragments, and reveal the factors which are behind this effect. We have performed a systematic analysis of the same sequence variants of exon 11 of the BRCA1 gene in DNA fragments of three different lengths using the combined single-strand conformation polymorphism (SSCP) and heteroduplex analysis (DA) by capillary electrophoresis (CE). There are two major structural factors responsible for the reduced mutation detection rate in long amplicons. The first is increased contribution from other secondary structure modules and domains in longer fragments, which mask the structural change induced by the mutation. The second is higher frequency of single-nucleotide polymorphisms (SNPs) including common polymorphisms in longer fragments. This makes it necessary to distinguish the structural effect of the mutation from that of each polymorphic variant, which is often difficult to achieve. Taking these factors into account, an efficient scanning of genes for sequence variants by conformation-sensitive methods may be performed.

Replication study supports evidence for linkage to 9p24 in obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a severe psychiatric illness that is characterized by intrusive and senseless thoughts and impulses (obsessions) and by repetitive behaviors (compulsions). Family, twin, and segregation studies support the presence of both genetic and environmental susceptibility factors, and the only published genome scan for OCD identified a candidate region on 9p24 at marker D9S288 that met criteria for suggestive significance (Hanna et al. 2002). In an attempt to replicate this finding, we genotyped 50 pedigrees with OCD, using microsatellite markers spanning the 9p24 candidate region, and analyzed the data, using parametric and nonparametric linkage analyses under both a narrow phenotype model (DSM-IV OCD definite; 41 affected sib pairs) and a broad phenotype model (DSM-IV OCD definite and probable; 50 affected sib pairs). Similar to what was described by Hanna et al. (2002), our strongest findings came with the dominant parameters and the narrow phenotype model: the parametric signal peaked at marker D9S1792 with an HLOD of 2.26 ( alpha =0.59), and the nonparametric linkage signal (NPL) peaked at marker D9S1813 with an NPL of 2.52 (P=.006). These findings are striking in that D9S1813 and D9S1792 lie within 0.5 cM (<350 kb) of the original 9p24 linkage signal at D9S288; furthermore, pedigree-based association analyses also implicated the 9p24 candidate region by identifying two markers (D9S288 and GATA62F03) with modest evidence (P=.046 and .02, respectively) for association.

Genetics of anxiety disorders

There is considerable evidence that genetic determinants play a major role in the etiology of anxiety. Investigations into susceptibility genes for anxiety are well underway, particularly for panic disorder and obsessive-compulsive disorder and more broadly defined anxiety-related traits, such as neuroticism and harm avoidance. This review will discuss some of the core issues related to diagnosis and molecular genetic methodology, followed by a review of recent molecular genetic findings for anxiety. The authors will attempt to highlight the numerous convergent and exciting findings. Given the rapid acceleration in knowledge of the human genome, a more definitive understanding of the genetic roots of these complex conditions may be anticipated in the relatively near future.

Association of a glutamate (NMDA) subunit receptor gene (GRIN2B) with obsessive-compulsive disorder: a preliminary study

RATIONALE

Recent investigation suggests that a reversible glutamatergically mediated thalamocortical-striatal dysfunction may serve as a reliable pathophysiological and treatment response marker for obsessive-compulsive disorder (OCD). We postulated that N-methyl- d-aspartate (NMDA) receptors were involved in OCD, and specifically that polymorphisms in the 3' untranslated region of GRIN2B (glutamate receptor, ionotropic, N-methyl- d-aspartate 2B) were associated with OCD in affected families.

OBJECTIVES

The objective of this investigation was to test the association between GRIN2B variants and transmission of the OCD trait using a family-based design.

METHODS

Using the Family Based Association Test (FBAT), we tested for association with OCD diagnosis in 130 families, and also performed a haplotype analysis. FBAT was additionally used in a subset of 98 families to test for association with the quantitative phenotype of lifetime OCD symptom severity. RESULTS. Under a non-additive model of inheritance, the 5072T/G variant was significantly associated with OCD even after correcting for the number of models tested ( P=0.014). In addition, there was a significant positive association with OCD diagnosis ( P=0.002) for the 5072G-5988T haplotype under the recessive model.

CONCLUSIONS

Although preliminary and requiring replication in larger samples, these results provide evidence that GRIN2B may be associated with susceptibility to OCD. Coupled with basic neuroscience and clinical neuroimaging findings in patients with OCD, our results provide new and converging support for the role of altered glutamatergic neurotransmission in the pathogenesis of OCD.

Genome-wide linkage analysis of families with obsessive-compulsive disorder ascertained through pediatric probands

The goal of this study was to identify chromosomal regions likely to contain susceptibility alleles for early-onset obsessive-compulsive disorder (OCD). A genome scan was done in 56 individuals from seven families ascertained through pediatric OCD probands; 27 of the 56 subjects had a lifetime diagnosis of definite OCD. Denser mapping of regions on chromosomes 2, 9, and 16 was subsequently done with those subjects and ten additional subjects from the largest family in the study. Direct interviews were completed with 65 of the 66 genotyped individuals. Relatives were interviewed blind to proband status. Of the 65 interviewed individuals, 32 had a lifetime diagnosis of definite OCD. Three of the seven probands had a history of Tourette disorder. Two of the 25 relatives with OCD had a tic history, whereas none of the 33 relatives without OCD had tics. The genome scan consisted of 349 microsatellite markers with an average between-marker distance of 11.3 centiMorgan (cM). Fine mapping was done with 24 additional markers at an average spacing of 1.6 cM. Parametric and nonparametric linkage analyses were conducted using GENEHUNTER(+). The maximum multipoint LOD score with a dominant model was 2.25 on 9p. However, with fine mapping and additional subjects, that LOD score decreased to 1.97. The maximum multipoint nonparametric LOD* score was 1.73 on 19q. The maximum multipoint LOD score with a recessive model was 1.40 on 6p. The results provide suggestive evidence for linkage on 9p and identify regions requiring further study with much larger samples.

Genomewide scan of hoarding in sib pairs in which both sibs have Gilles de la Tourette syndrome

A genome scan of the hoarding phenotype (a component of obsessive-compulsive disorder) was conducted on 77 sib pairs collected by the Tourette Syndrome Association International Consortium for Genetics (TSAICG). All sib pairs were concordant for a diagnosis of Gilles de la Tourette syndrome (GTS). However, the analyses reported here were conducted for hoarding as both a dichotomous trait and a quantitative trait. Not all sib pairs in the sample were concordant for hoarding. Standard linkage analyses were performed using GENEHUNTER and Haseman-Elston methods. In addition, novel analyses with a recursive-partitioning technique were employed. Significant allele sharing was observed for both the dichotomous and the quantitative hoarding phenotypes for markers at 4q34-35 (P=.0007), by use of GENEHUNTER, and at 5q35.2-35.3 (P=.000002) and 17q25 (P=.00002), by use of the revisited Haseman-Elston method. The 4q site is in proximity to D4S1625, which was identified by the TSAICG as a region linked to the GTS phenotype. The recursive-partitioning technique examined multiple markers simultaneously. Results suggest joint effects of specific loci on 5q and 4q, with an overall P value of.000003. Although P values were not adjusted for multiple comparison, nearly all were much smaller than the customary significance level of.0001 for genomewide scans.

Genetic and imaging strategies in obsessive-compulsive disorder: potential implications for treatment development

In recent years, advances in brain research have resulted in a striking strategic shift in studies designed to develop new, effective treatments for neuropsychiatric disorders. This involves a multidisciplinary approach with recursive interactions among respective disciplines with the ultimate goal of contributing to treatment development. In this review we focus on treatment implications of brain imaging and molecular and pharmacogenetic studies in obsessive-compulsive disorder. Translational components of this research are addressed, including the potential for integrating advances in brain imaging and molecular and pharmacogenetic assessments as they may potentially relate to neurodiagnostic assessment and treatment development. Studies of putative susceptibility alleles in obsessive-compulsive disorder involving the serotonergic, glutamatergic, and dopaminergic systems may provide a focus for these divergent approaches. Taken together, neuroimaging and genetic methods may ultimately lead to a mechanistic understanding of the pathogenesis and maintenance of neuropsychiatric disorders such as obsessive-compulsive disorder that may, in turn, result in the development of new neurodiagnostic and treatment approaches.