Mu opioid receptor gene as a candidate for the study of obsessive compulsive disorder with and without tics

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.

Ondansetron Augmentation for Treatment-Resistant Obsessive-Compulsive Disorder: A Randomized Placebo-Controlled Clinical Trial

Background: Serotonin and dopamine are involved in the development of obsessive-compulsive disorder (OCD). Approximately 40% of OCD patients do not respond to the first-line therapy of treatment using selective serotonin reuptake inhibitors. Reportedly, the response to the treatment is increased by enhancing dopamine blockers. Objectives: The purpose of this study was to evaluate the efficacy and immunogenicity of ondansetron as a booster in the treatment of OCD patients. Methods: The present double-blind, randomized clinical trial (RCT) was conducted on 40 patients (16 males and 24 females) aged 18 to 60 years who met the DSM-V-TR-based OCD diagnostic criteria and had a minimum score of 16 on the Yale-Brown Obsessive Compulsive Scale (Y-BOCS). The patients were randomized to receive standard treatment and ondansetron (8 mg/day) or placebo for 12 weeks. They were examined using Y-BOCS and side-effect checklist at baseline, fourth, eighth, and twelfth weeks. Results: The patients in both groups were homogeneous and comparable in terms of age, marital sex status, type of obsession, anxiety, depression, age at the onset of disease, and the duration of disease. The Y-BOCS scores in the intervention and placebo groups were 27.15 ± 3.94 vs. 26.15 ± 4.94 at baseline, 25.40 ± 3.75 vs. 25.00 ± 4.79 in the fourth week, 20.85 ± 3.69 vs. 24.05 ± 4.97 (P = 0.026) in the eighth week, and 17.95 ± 3.43 vs. 21.65 ± 4.85 (P = 0.008) in the twelfth week, respectively. Significant changes occurred between the two groups at weeks 8 and 12; the difference between the two groups was significant (P = 0.015), whereas no significant difference was observed between the two groups before week 8. Conclusions: This 12-week, double-blind, and randomized clinical trial showed that ondansetron was a booster agent with a significant effect on patients with moderate to severe OCD. This study also showed that ondansetron is generally well tolerated by OCD patients. The response to the treatment also increased from the eighth week of treatment onwards. The severity of the disease was decreased at the end of the ondansetron intervention. The adjunct ondansetron treatment was recommended for OCD patients

Psychopharmacological Treatment of Obsessive-Compulsive Disorder (OCD)

Background:

Obsessive-compulsive disorder (OCD) is associated with affective and cognitive symptoms causing personal distress and reduced global functioning. These have considerable societal costs due to healthcare service utilization.

Objective:

Our aim was to assess the efficacy of pharmacological interventions in OCD and clinical guidelines, providing a comprehensive overview of this field.

Methods:

We searched the PubMed database for papers dealing with drug treatment of OCD, with a specific focus on clinical guidelines, treatments with antidepressants, antipsychotics, mood stabilizers, off-label medications, and pharmacogenomics.

Results:

Prolonged administration of selective serotonin reuptake inhibitors (SSRIs) is most effective. Better results can be obtained with a SSRI combined with cognitive behavioral therapy (CBT) or the similarly oriented exposure and response prevention (ERP). Refractory OCD could be treated with different strategies, including a switch to another SSRI or clomipramine, or augmentation with an atypical antipsychotic. The addition of medications other than antipsychotics or intravenous antidepressant administration needs further investigation, as the evidence is inconsistent. Pharmacogenomics and personalization of therapy could reduce treatment resistance.

Conclusions:

SSRI/clomipramine in combination with CBT/ERP is associated with the optimal response compared to each treatment alone or to other treatments. New strategies for refractory OCD are needed. The role of pharmacogenomics could become preponderant in the coming years.

Comparing the efficacy of ondansetron and granisetron augmentation in treatment-resistant obsessive-compulsive disorder: a randomized double-blind placebo-controlled study

This study aimed to assess the efficacy and tolerability of ondansetron vs. granisetron in patients with treatment-resistant obsessive-compulsive disorder. A randomized clinical trial conducted on 135 patients with a Diagnostic and Statistical Manual of Mental Disorders-IV (DSM-IV) diagnosis of obsessive-compulsive disorder, who were treatment-resistant and receiving stable treatment with selective serotonin reuptake inhibitors and antipsychotic, received 14 weeks (phase I, intervention period) of placebo (n = 45), ondansetron (n = 45, 4 mg), and granisetron (n = 45, 2 mg) daily augmentations. Patients were rated every 2 weeks using the Yale-Brown Obsessive Compulsive Scale. Upon completion of intervention course, patients were followed for 4 weeks (phase II, discontinuation period). The collected data were analyzed in SPSS Version 22, with χ test; Fisher's exact test and independent t-test, according to the intention-to-treat principle. Two-factor repeated measure analysis of variance was used to compare score changes over phases. P < 0.05 was considered to be statistically significant. At week 14, reduction in Yale-Brown Obsessive Compulsive Scale scores in ondansetron, granisetron and placebo groups was 41.5%, 39.7% and 15.2%, respectively (P = 0.001). Complete response in the ondansetron group was significantly higher than in the granisetron group ((P = 0.041), risk ratio (95% confidence interval) = 2.33 (1.18-3.045)]. Relapse occurred by three (7.31%) patients in the granisetron group, whereas it was not seen in the ondansetron group [P < 0.001, risk ratio (95% confidence interval) = 2.81 (1.016-4.51)]. The results of this present study confirm the benefit of using ondansetron and granisetron as augmenting agents in treatment-resistant obsessive-compulsive disorder. Our results supported the potential superiority of ondansetron compared to granisetron. This needs to be confirmed in further placebo-controlled augmentation studies. RANDOMIZED CONTROLLED TRIAL CLINICAL TRIAL REGISTRATION NUMBER:: IRCT20130726014170N2.

Animal models of obsessive-compulsive disorder: utility and limitations

Obsessive-compulsive disorder (OCD) is a disabling and common neuropsychiatric condition of poorly known etiology. Many attempts have been made in the last few years to develop animal models of OCD with the aim of clarifying the genetic, neurochemical, and neuroanatomical basis of the disorder, as well as of developing novel pharmacological and neurosurgical treatments that may help to improve the prognosis of the illness. The latter goal is particularly important given that around 40% of patients with OCD do not respond to currently available therapies. This article summarizes strengths and limitations of the leading animal models of OCD including genetic, pharmacologically induced, behavioral manipulation-based, and neurodevelopmental models according to their face, construct, and predictive validity. On the basis of this evaluation, we discuss that currently labeled "animal models of OCD" should be regarded not as models of OCD but, rather, as animal models of different psychopathological processes, such as compulsivity, stereotypy, or perseverance, that are present not only in OCD but also in other psychiatric or neurological disorders. Animal models might constitute a challenging approach to study the neural and genetic mechanism of these phenomena from a trans-diagnostic perspective. Animal models are also of particular interest as tools for developing new therapeutic options for OCD, with the greatest convergence focusing on the glutamatergic system, the role of ovarian and related hormones, and the exploration of new potential targets for deep brain stimulation. Finally, future research on neurocognitive deficits associated with OCD through the use of analogous animal tasks could also provide a genuine opportunity to disentangle the complex etiology of the disorder.

Ondansetron augmentation in patients with obsessive-compulsive disorder who are inadequate responders to serotonin reuptake inhibitors: improvement with treatment and worsening following discontinuation

OBJECT

The aim of this study was to evaluate low-dose ondansetron as an augmentation strategy in patients with obsessive-compulsive disorder (OCD) who do not adequately respond to serotonin reuptake inhibits (SRIs).

METHODS

Twenty-one OCD patients who had not responded adequately to an SRI received 12 weeks of single-blind ondansetron augmentation initiated at 0.25mg BID for 2 weeks, and titrated to 0.5mg BID for an additional 10 weeks. Patients were rated every two weeks using the Yale-Brown Obsessive Compulsive Scale (YBOCS) and Clinical Global Impressions Scale (CGI). Treatment response was defined as an additional 25% reduction in YBOCS score from the score at the initiation of ondansetron augmentation, an end of treatment YBOCS score of ≤ 24 and a CGI-Improvement (CGI-I) score of ≤ 2. Upon completion of treatment course patients were followed for 4 weeks.

RESULTS

At week 12, twelve of the 21 (57%) patients were responders. The average reduction in the YBOCS score for the overall group was 27.2%. Responders had an average 44% YBOCS score reduction and 76.9% CGI-I reduction. After discontinuation of ondansetron the YBOCS worsened an average of 15.5% in the entire sample and 38.3% in the responder subsample. No clinically meaningful side effects were reported.

CONCLUSION

OCD patients who do not adequately respond to an SRI may benefit from augmentation with a low-dose of ondansetron. This may provide an alternative approach to augmentation with atypical antipsychotic agents, with a more favorable safety profile.

Buprenorphine augmentation in the treatment of refractory obsessive-compulsive disorder

BACKGROUND

OCD is often refractory to treatment. There is a need for the development of new, non-invasive treatments for severe OCD.

RATIONALE

There is evidence that opiates can be a useful adjunctive treatment in OCD. We summarise our experience with sublingual buprenorphine augmentation of standard pharmacological management of severe OCD.

METHODS

Patients were recruited from a standard psychiatric outpatient clinic and gave their consent to the treatment trial. The severity of the OCD was rated with the Y-BOCS. The buprenorphine was introduced to their existing medication regime at a low dose and the dose increased according to response. In order to gauge the reproducibility of the response the buprenorphine was withdrawn and then reintroduced once symptoms had returned.

RESULTS

4 out of 7 patients with treatment resistant OCD showed a 30% reduction in the Y-BOCS score following buprenorphine augmentation. 3 of the responders were comorbid for other Axis 1 diagnoses. All of the responders had shown some improvement with SSRIs or clomipramine. Non-responders had not shown any improvement with either antidepressant or antipsychotic drugs. Typically improvement appeared within 2 days of initiating buprenorphine and waned within 1 to 2 days of its discontinuation. The dose of buprenorphine required varied between 400 µg and 600 µg a day. One responder managed on alternate day dosing. Reintroduction of buprenorphine resulted in symptom control within 2 to 3 days. The buprenorphine treatment was not associated with significant side-effects and the improvement was maintained without progressive dose escalation.

CONCLUSIONS

Buprenorphine augmentation of standard treatment for OCD can result in clinically meaningful improvement in a proportion of refractory OCD cases. Further treatment trials are indicated.

Opioids and anxiety

The opioid system plays a crucial role in the neural modulation of anxiety. The involvement of opioid ligands and receptors in physiological and dysfunctional forms of anxiety is supported by findings from a wide range of preclinical and clinical studies, including clinical trials, experimental research, and neuroimaging, genetic, and epidemiological data. In this review we provide a summary of studies from a variety of research disciplines to elucidate the role of the opioid system in the neurobiology of anxiety. First, we report data from preclinical studies using animal models to examine the modulatory role of central opioid system on defensive responses conducive to fear and anxiety. Second, we summarize the human literature providing evidence that clinical and experimental human studies are consistent with preclinical models. The implication of these data is that activation of the opioid system leads to anxiolytic responses both in healthy subjects and in patients suffering from anxiety disorders. The role of opioids in suppressing anxiety may serve as an adaptive mechanism, collocated in the general framework of opioid neurotransmission blunting acute negative and distressing affective responses.

Pharmacogenomics of the human µ-opioid receptor

The µ-opioid receptor is a primary target for clinically important opioid analgesics, including morphine, fentanyl and methadone. Many genetic variations have been identified in the human µ-opioid receptor MOP gene (OPRM1), and their implications have been reported in the effects of opioid drugs and susceptibility to drug dependence. Interestingly, agonistic and antagonistic opioid effects are inversely associated with the A118G polymorphism genotype. The A118G polymorphism may also be associated with substance dependence and susceptibility to other disorders, including epilepsy and schizophrenia. The IVS1+A21573G, IVS1-T17286C, and TAA+A5359G polymorphisms in the OPRM1 gene may be associated with alcohol, opioid and tobacco dependence, respectively. However, some studies have failed to confirm the correlations between the polymorphisms and opioid effects and substance dependence. Further studies are needed to elucidate the molecular mechanisms underlying the effects of OPRM1 polymorphisms.

Overview of genetics and obsessive-compulsive disorder

This paper reviews the current state of research into the genetics of obsessive-compulsive disorder (OCD). Heredity has a major role in OCD etiology. This evidence comes from several methodological approaches such as family, twin, and segregation analysis studies. A major single gene effect as well as a polygenic hypothesis has been suggested based on segregation studies. In addition, candidate gene association and linkage analyses have shown not only one gene, but a few interesting genes and areas of the genome that may be relevant in OCD. In this search for genes, new definitions of the OCD phenotype have emerged, and some of them may be considered intermediate phenotypes between the gene effect and OCD-DSM-IV diagnosis. The phenotypic and genetic heterogeneity of OCD magnifies the challenge of locating susceptibility genes; at the same time, the identification of vulnerability genes will elucidate the identification of subtypes or dimensions of the disorder. Therefore research strategies that take advantage of clinical subtyping and that redefine the OCD phenotype in the context of genetic studies may potentially contribute to the nosology of OCD and ultimately pathophysiology. There is a lack of understanding about how genes and environment interact in OCD. However, there are some reports that will be discussed, which have attempted to evaluate how the environment contributes to OCD.

Obsessive-compulsive disorder: diagnostic and treatment issues

This article reviews current issues in the diagnosis and treatment of obsessive-compulsive disorder (OCD). The introduction of the selective serotonin reuptake inhibitors and of cognitive-behavioral therapy were significant advances for treating OCD. Nevertheless, there is a need to improve awareness of OCD and its management, and to develop novel approaches to treatment-refractory patients. Although the diagnostic criteria for OCD have remained unchanged for some time, there are several areas where potential modification may be useful. There is a growing evidence base on OCD symptom dimensions and subtyping, and it is timely to consider incorporating some of these emerging data into diagnostic classification systems.

Assessing the validity of current mouse genetic models of obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) is a disorder characterized by unwanted and intrusive thoughts, images, or impulses and/or repetitive behavior. OCD is a major cause of disability; however, the genetic factors and pathophysiological mechanisms underlying this complex, heterogeneous disorder remain largely unknown. During the past decade, a number of putative mouse genetic models of OCD have been developed for the purpose of studying the neural mechanisms underlying this disorder and developing novel treatments. This review presents and evaluates these experimental preparations to date. Models using knockout or transgenic approaches, as well as those examining variation in genetically diverse populations, are evaluated and discussed.

Naltrexone augmentation in OCD: a double-blind placebo-controlled cross-over study

Current treatments for Obsessive Compulsive Disorder (OCD) rely primarily on serotonergic mechanisms. However, approximately 30% of patients do not respond to serotonin reuptake inhibitors and remain chronically ill. Given the behavioral similarities between some of the compulsive behaviors in OCD and addiction, we hypothesized that the opioid antagonist naltrexone might attenuate compulsions in OCD as well. The effect of naltrexone augmentation to SRI was compared to placebo in 10 OCD outpatients who had not responded to an adequate dose of SSRI or clomipramine for at least 2 months. Participants underwent 5 weeks of treatment with naltrexone or placebo (and 1 week of tapering) in a randomized, double-blind, cross-over design. Patients were evaluated weekly using the Y-BOCS, CGI, HAM-A, and MADRS scales. A two-way repeated measures MANOVA revealed no significant effect for Y-BOCS. However, while receiving naltrexone, patients had significantly higher scores on CGI, MADRS and HAM-A as compared to placebo. The lack of significant findings on OC symptoms could be due to either ceiling effect or alternatively, due to a non-specific exacerbation on anxiety and depression but not on OC symptoms.

Neurobiologie bei Tic- und Zwangsstörungen

Zusammenfassung. Erst in den letzten Jahren wird auch in der Forschung vermehrtes Augenmerk auf die Überschneidung von Tic- und Zwangsstörungen gerichtet. Während in Übersichtsarbeiten zum gemeinsamen Auftreten von Tic- und Zwangsstörungen die zahlreichen Befunde zu Phänomenologie, begleitender Psychopathologie, Epidemiologie und daraus resultierenden Therapieimplikationen breiten Raum einnehmen, sind die Untersuchungsergebnisse hinsichtlich ätiologischer und pathophysiologischer Gemeinsamkeiten in entsprechenden Arbeiten unterrepräsentiert. Daher wird mit dieser Arbeit ein Überblick über den aktuellen neurobiologischen Forschungsstand zu den Gemeinsamkeiten und Unterschieden von Tic- und Zwangsstörungen gegeben.

Estado atual da clínica psiquiátrica do transtorno obsessivo-compulsivo

Este artigo revisa a literatura sobre o transtorno obsessivocompulsivo com o objetivo de informar o estado atual da pesquisa científica nesse tema. Os autores citam a literatura internacional buscando enfatizar a pesquisa nacional, principalmente a pesquisa do seu grupo, o Projeto Transtornos do espectro Obsessivo-compulsivo.

Role of atypical opiates in OCD. Experimental approach through the study of 5-HT(2A/C) receptor-mediated behavior

RATIONALE

The selective serotonin (5-HT) reuptake inhibitors (SSRIs) represent the first-line pharmacotherapy for obsessive-compulsive disorder (OCD), and atypical antipsychotic drugs, which block 5-HT2A receptors, are used in augmentation strategies. Opiate drugs are also effective in treatment-refractory OCD and Tourette syndrome. The 5-HT2A-related behavior (i.e., head twitch) has been related with tics, stereotypes, and compulsive symptoms observed in Tourette syndrome and OCD.

OBJECTIVES

The aim of this study was to explore whether 5-HT2A-related behavior is affected by atypical opiate drugs.

MATERIALS AND METHODS

Head-twitch response was induced in mice by administration of either 5-hydroxytryptophan (5-HTP) or the 5-HT2A/C agonist (+/-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI). Dose-effect curves of atypical opiate drugs [(+/-)-tramadol, (-)-methadone and levorphanol], morphine, and other psychoactive drugs (fluvoxamine, desipramine, nefazodone, and clozapine) were performed. Opioid mechanisms were investigated by administration of naloxone.

RESULTS

All the opiates tested reduced both 5-HTP and DOI-induced behavior in a naloxone-reversible fashion, atypical opiates being more effective. The effects of the other drugs depended on the protocol, clozapine being the most effective.

CONCLUSIONS

Combined 5-HT and opioid properties result in a greater efficacy in antagonizing 5-HT2A-related behavior. These results provide behavioral evidence to support convergent effects of the 5-HT and opioid systems in discrete brain areas, offering the potential for therapeutic advances in the management of refractory stereotypes and compulsive behaviors.

Relevance of frequent mu-opioid receptor polymorphisms for opioid activity in healthy volunteers

Polymorphisms in the mu-opioid receptor gene (OPRM1) are primary candidate sources of clinical variability in opioid therapy. Apart from the 118A>G single nucleotide polymorphism, nothing is known about the role of OPRM1 mutations in opioid therapy. The influence of the OPRM1 mutations on opioid pharmacodynamics was assessed in pooled data from 31 healthy volunteers obtained in previous studies with available plasma concentrations and pupil diameters after intravenous administration of morphine or morphine-6-glucuronide (M6G). A total of 24 candidate ORPM1 mutations were screened for and those found at an allelic frequency of at least 5% in the 31 subjects were analyzed for functional consequences, using population pharmacokinetic-pharmacodynamic modeling of the miotic effects of the opioids as a reliable and sensitive surrogate parameter of the central nervous opioid effects. Polymorphisms at an allelic frequency of > or =5% (n=310) were 118A>G in exon 1 (11.5%), the IVS2-31G>A (8.9%) and IVS2-691C>G (44.5%) SNPs in intron 2. The 118A>G SNP significantly increased the values of EC50 by a factor of more than 2 (non-mutated: EC50,morphine=30 nmol/l, EC50,M6G=750 nmol/l, 118G carriers: EC50,morphine=66 nmol/l, EC50,M6G=1650 nmol/l), whereas the IVS2-691C>G SNP had no effect. Based on morphine and M6G, the present analysis encourages focusing on the 118A>G SNP when investigating the role of OPRM1 mutations for the activity of opioid analgesics. Other OPRM1 mutations are probably less important either owing to low allelic frequency or due to poor indications for functional consequences. This applies to opioid potency in the context of opioid therapy but not to pain processing or substance addiction, in which opioid receptors are involved but other or additional OPRM1 mutations may be important.

Tic disorders and obsessive compulsive disorder: where is the link?

Over the last years evidence on the overlap between tic-disorders (TD) and obsessive compulsive behavior/disorder (OCB/OCD) has increased. The main focus of research have been the phenomenological and epidemiological similarities and differences in samples of different age, primary diagnosis (TD vs. OCD) including the co-occurrence of both. Unfortunately, only a minority of studies included all three groups (TD, TD + OCD, OCD). Nevertheless, new insight concerning possible subtypes for both TD and OCD has been gained. While some authors concentrated on OCD with/without tics we will summarize the field of TD and OCB/OCD from the viewpoint of tics, since OCB plays an important role in patients with TD. Thereby we will not only sharpen the clinicans' awareness of known differences in phenomenology, epidemiology, genetics and neurobiology, aimed to improve their diagnoses and treatment but also highlight the gaps of knowledge and discuss possibilities for further research in this field.

Estudos de associação entre transtorno obsessivo-compulsivo e genes candidatos: uma revisão

OBJETIVO: Nos últimos anos, o papel dos genes dos sistemas serotoninérgicos e dopaminérgicos tem sido sistematicamente investigado em pacientes com transtorno obsessivo-compulsivo (TOC), uma vez que esses neurotransmissores apresentam uma provável implicação na fisiopatologia do TOC. Este artigo objetiva revisar os principais resultados de estudos de associação entre genes candidatos e TOC. MÉTODOS: Revisão da literatura na base de dados Medline até agosto de 2006, utilizando as palavras-chave obsessive-compulsive disorder (OCD) e/ou gene(s), polymorphism(s), genetics. RESULTADOS: Inúmeros estudos têm apresentado resultados negativos ao compararem pacientes com TOC e controles, entretanto resultados positivos têm sido observados em pacientes com TOC com características clínicas particulares (sexo, idade de início, dimensão ou gravidade dos sintomas obsessivos ou compulsivos e presença de tiques). CONCLUSÃO: Para garantir a continuidade do avanço de estudos genéticos, é necessária a identificação de subgrupos homogêneos de pacientes com TOC. Diante desses grupos, será possível delinear endofenótipos confiáveis que permitam explorar de forma mais específica a contribuição dos diferentes genes na patogênese da doença.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

How individual sensitivity to opiates can be predicted by gene analyses

Opiate analgesics are widely used and abused drugs. Individual differences in opiate sensitivity can hamper effective pain treatments and increase risks of drug abuse. Although genetic factors might affect individual differences in opiate sensitivity, scientific evidence for specific genetic mechanisms that underlie these differences has been sparse. Recent studies using inbred and knockout mice have revealed that the mu opioid peptide (MOP) receptor encoded by the Oprm1 gene has a mandatory role in the analgesic and addictive properties of opiate drugs. Increasing evidence suggests that differences in Oprm1 gene sequences affect the amount of Oprm1 mRNA and sensitivity to opiates, and >100 polymorphisms have been identified in the human OPRM1 gene, some of which are related to vulnerability to drug dependence in some populations. Rapid advances in this research field are leading to improved understanding of the relationships between gene polymorphisms and opiate sensitivities that will enable more-accurate prediction of the opiate sensitivity and opiate requirements in individual patients.

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.

Are μ-opioid receptor polymorphisms important for clinical opioid therapy?

Mutations in the mu-opioid receptor--the primary site of action of opioid analgesics--are candidates for the variability of clinical opioid effects. This has been substantiated by recent advances in genetic research. A common mu-opioid receptor polymorphism was associated with higher demands for alfentanil or morphine for pain relief. It also decreased the potency of morphine for pupil constriction and experimental analgesia, but its molecular mechanisms are unclear. Another opioid receptor mutation greatly impaired receptor signalling in vitro, but is very rare. The accumulated evidence provides a solid basis for continuing research that should address the underlying molecular mechanisms and the role and benefits of OPRM1 genotyping for clinical pain therapy.

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.