Antipsychotic-induced tardive dyskinesia and the Ser9Gly polymorphism in the DRD3 gene: a meta analysis

The polymorphisms of candidate pharmacokinetic and pharmacodynamic genes and their pharmacogenetic impacts on the effectiveness of risperidone maintenance therapy among Saudi children with autism

BACKGROUND

Antipsychotics, including risperidone (RIS), are frequently indicated for various autism spectrum disorder (ASD) manifestations; however, "actionable" PGx testing in psychiatry regarding antipsychotic dosing and selection has limited applications in routine clinical practice because of the lack of standard guidelines, mostly due to the inconsistency and scarcity of genetic variant data. The current study is aimed at examining the association of RIS effectiveness, according to ABC-CV and CGI indexes, with relevant pharmacokinetics (PK) and pharmacodynamics (PD) genes.

METHODS

Eighty-nine ASD children who received a consistent RIS-based regimen for at least 8 weeks were included. The Axiom PharmacoFocus Array technique was employed to generate accurate star allele-predicted phenotypes of 3 PK genes (CYP3A4, CYP3A5, and CYP2D6). Genotype calls for 5 candidate PD receptor genes (DRD1, DRD2, DRD3, HTR2C, and HTR2A) were obtained and reported as wild type, heterozygous, or homozygous for 11 variants.

RESULTS

Based on the ABC total score, 42 (47.2%) children were classified as responders, while 47 (52.8%) were classified as nonresponders. Multivariate logistic regression analyses, adjusted for nongenetic factors, suggested nonsignificant impacts of the star allele-predicted phenotypes of all 3 PK genes on improvement in ASD symptoms or CGI scores. However, significant positive or negative associations of certain PD variants involved in dopaminergic and serotonergic pathways were observed with specific ASD core and noncore symptom subdomains. Our significant polymorphism findings, mainly those in DRD2 (rs1800497, rs1799978, and rs2734841), HTR2C (rs3813929), and HTR2A (rs6311), were largely consistent with earlier findings (predictors of RIS effectiveness in adult schizophrenia patients), confirming their validity for identifying ASD children with a greater likelihood of core symptom improvement compared to noncarriers/wild types. Other novel findings of this study, such as significant improvements in DRD3 rs167771 carriers, particularly in ABC total and lethargy/social withdrawal scores, and DRD1 rs1875964 homozygotes and DRD2 rs1079598 wild types in stereotypic behavior, warrant further verification in biochemical and clinical studies to confirm their feasibility for inclusion in a PGx panel.

CONCLUSION

In conclusion, we provide evidence of potential genetic markers involved in clinical response variability to RIS therapy in ASD children. However, replication in prospective samples with greater ethnic diversity and sample sizes is necessary.

Dopaminergic and norepinephrinergic modulation of endogenous event-related potentials: A systematic review and meta-analysis

Event-related potentials (ERPs) represent the cortical processing of sensory, motor or cognitive functions invoked by particular events or stimuli. A current theory posits that the catecholaminergic neurotransmitters dopamine (DA) and norepinephrine (NE) modulate a number of endogenous ERPs during various cognitive processes. This manuscript aims to evaluate a leading neurotransmitter hypothesis with a systematic overview and meta-analysis of pharmacologic DA and NE manipulation of specific ERPs in healthy subjects during executive function. Specifically, the frontally-distributed P3a, N2, and Ne/ERN (or error-related negativity) are supposedly modulated primarily by DA, whereas the parietally-distributed P3b is thought to be modulated by NE. Based on preceding research, we refer to this distinction between frontally-distributed DA-sensitive and parietally-distributed NE-sensitive ERP components as the Extended Neurobiological Polich (ENP) hypothesis. Our systematic review and meta-analysis indicate that this distinction is too simplistic and many factors interact with DA and NE to influence these specific ERPs. These may include genetic factors, the specific cognitive processes engaged, or elements of study design, i.e. session or sequence effects or data-analysis strategies.

A preclinical secondary pharmacology resource illuminates target-adverse drug reaction associations of marketed drugs

In vitro secondary pharmacology assays are an important tool for predicting clinical adverse drug reactions (ADRs) of investigational drugs. We created the Secondary Pharmacology Database (SPD) by testing 1958 drugs using 200 assays to validate target-ADR associations. Compared to public and subscription resources, 95% of all and 36% of active (AC50 < 1 µM) results are unique to SPD, with bias towards higher activity in public resources. Annotating drugs with free maximal plasma concentrations, we find 684 physiologically relevant unpublished off-target activities. Furthermore, 64% of putative ADRs linked to target activity in key literature reviews are not statistically significant in SPD. Systematic analysis of all target-ADR pairs identifies several putative associations supported by publications. Finally, candidate mechanisms for known ADRs are proposed based on SPD off-target activities. Here we present a freely-available resource for benchmarking ADR predictions, explaining phenotypic activity and investigating clinical properties of marketed drugs.

Genetic Factors Associated With Tardive Dyskinesia: From Pre-clinical Models to Clinical Studies

Tardive dyskinesia is a severe motor adverse event of antipsychotic medication, characterized by involuntary athetoid movements of the trunk, limbs, and/or orofacial areas. It affects two to ten patients under long-term administration of antipsychotics that do not subside for years even after the drug is stopped. Dopamine, serotonin, cannabinoid receptors, oxidative stress, plasticity factors, signaling cascades, as well as CYP isoenzymes and transporters have been associated with tardive dyskinesia (TD) occurrence in terms of genetic variability and metabolic capacity. Besides the factors related to the drug and the dose and patients’ clinical characteristics, a very crucial variable of TD development is individual susceptibility and genetic predisposition. This review summarizes the studies in experimental animal models and clinical studies focusing on the impact of genetic variations on TD occurrence. We identified eight genes emerging from preclinical findings that also reached statistical significance in at least one clinical study. The results of clinical studies are often conflicting and non-conclusive enough to support implementation in clinical practice.

Current perspectives on the epidemiology and burden of tardive dyskinesia: a focused review of the clinical situation in Japan

Tardive dyskinesia (TD) is a movement disorder that can develop with the use of dopamine receptor-blocking agents and is most commonly caused by antipsychotics. The use of antipsychotics is expanding, which may lead to an increased number of patients experiencing TD. To summarise the current knowledge of the epidemiology and risk factors for TD in Japan, we reviewed articles related to the current state of knowledge around TD identified through a PubMed search, and held a roundtable discussion of experts in Japan on 9 September 2021 to form the basis of the opinion presented within this review. The true prevalence of TD among patients treated with antipsychotics is not well characterised; it is reported to be between 15% and 50% globally and between 6.5% and 7.7% in Japan. Potential barriers to timely treatment of TD include the stigma surrounding mental health issues and the lack of data regarding TD in Asian patients. This review summarises the current knowledge of the epidemiology, challenges to TD diagnosis and risk factors for TD in Japan. Recent strategies for symptom monitoring and early diagnosis, as well as consensus recommendations are included. Achieving a high level of awareness of TD among physicians who treat patients with psychiatric disorders is of great importance and physicians should ensure that patients with psychiatric disorders receiving antipsychotics are proactively monitored for signs of TD.

PLAIN LANGUAGE SUMMARY

Plain Language Summary (In Japanese).

VISUAL SUMMARY

Visual Summary (In Japanese).

Pharmacogenetics of Antipsychotic Treatment in Schizophrenia

Antipsychotics are the mainstay treatment for schizophrenia. There is large variability between individuals in their response to antipsychotics, both in efficacy and adverse effects of treatment. While the source of interindividual variability in antipsychotic response is not completely understood, genetics is a major contributing factor. The identification of pharmacogenetic markers that predict antipsychotic efficacy and adverse reactions is a growing area of research and holds the potential to replace the current trial-and-error approach to treatment selection in schizophrenia with a personalized medicine approach.In this chapter, we provide an overview of the current state of pharmacogenetics in schizophrenia treatment. The most promising pharmacogenetic findings are presented for both antipsychotic response and commonly studied adverse reactions. The application of pharmacogenetics to schizophrenia treatment is discussed, with an emphasis on the clinical utility of pharmacogenetic testing and directions for future research.

Genome wide study of tardive dyskinesia in schizophrenia

Tardive dyskinesia (TD) is a severe condition characterized by repetitive involuntary movement of orofacial regions and extremities. Patients treated with antipsychotics typically present with TD symptomatology. Here, we conducted the largest GWAS of TD to date, by meta-analyzing samples of East-Asian, European, and African American ancestry, followed by analyses of biological pathways and polygenic risk with related phenotypes. We identified a novel locus and three suggestive loci, implicating immune-related pathways. Through integrating trans-ethnic fine mapping, we identified putative credible causal variants for three of the loci. Post-hoc analysis revealed that SNPs harbored in TNFRSF1B and CALCOCO1 independently conferred three-fold increase in TD risk, beyond clinical risk factors like Age of onset and Duration of illness to schizophrenia. Further work is necessary to replicate loci that are reported in the study and evaluate the polygenic architecture underlying TD.

Akathisia and Restless Legs Syndrome: Solving the Dopaminergic Paradox

Akathisia is an urgent need to move that is associated with treatment with dopamine receptor blocking agents (DRBAs) and with restless legs syndrome (RLS). The pathogenetic mechanism of akathisia has not been resolved. This article proposes that it involves an increased presynaptic dopaminergic transmission in the ventral striatum and concomitant strong activation of postsynaptic dopamine D₁ receptors, which form complexes (heteromers) with dopamine D₃ and adenosine A₁ receptors. It also proposes that in DRBA-induced akathisia, increased dopamine release depends on inactivation of autoreceptors, whereas in RLS it depends on a brain iron deficiency-induced down-regulation of striatal presynaptic A₁ receptors.

The genetics of drug-related movement disorders, an umbrella review of meta-analyses

This umbrella review investigates which genetic factors are associated with drug-related movement disorders (DRMD), in an attempt to provide a synthesis of published evidence of candidate-gene studies. To identify all relevant meta-analyses, a literature search was performed. Titles and abstracts were screened by two authors and the methodological quality of included meta-analyses was assessed using 'the assessment of multiple systematic reviews' (AMSTAR) critical appraisal checklist. The search yielded 15 meta-analytic studies reporting on genetic variations in 10 genes. DRD3, DRD2, CYP2D6, HTR2A, COMT, HSPG2 and SOD2 genes have variants that may increase the odds of TD. However, these findings do not concur with early genome-wide association studies. Low-power samples are susceptible to 'winner's curse', which was supported by diminishing meta-analytic effects of several genetic variants over time. Furthermore, analyses pertaining to the same genetic variant were difficult to compare due to differences in patient populations, methods used and the choice of studies included in meta-analyses. In conclusion, DRMD is a complex phenotype with multiple genes that impact the probability of onset. More studies with larger samples using other methods than by candidate genes, are essential to developing methods that may predict the probability of DRMD. To achieve this, multiple research groups need to collaborate and a DRMD genetic database needs to be established in order to overcome winner's curse and publication bias, and to allow for stratification by patient characteristics. These endeavours may help the development of a test with clinical value in the prevention and treatment of DRMD.

Antipsychotic Behavioral Phenotypes in the Mouse Collaborative Cross Recombinant Inbred Inter-Crosses (RIX)

Schizophrenia is an idiopathic disorder that affects approximately 1% of the human population, and presents with persistent delusions, hallucinations, and disorganized behaviors. Antipsychotics are the standard pharmacological treatment for schizophrenia, but are frequently discontinued by patients due to inefficacy and/or side effects. Chronic treatment with the typical antipsychotic haloperidol causes tardive dyskinesia (TD), which manifests as involuntary and often irreversible orofacial movements in around 30% of patients. Mice treated with haloperidol develop many of the features of TD, including jaw tremors, tongue protrusions, and vacuous chewing movements (VCMs). In this study, we used genetically diverse Collaborative Cross (CC) recombinant inbred inter-cross (RIX) mice to elucidate the genetic basis of antipsychotic-induced adverse drug reactions (ADRs). We performed a battery of behavioral tests in 840 mice from 73 RIX lines (derived from 62 CC strains) treated with haloperidol or placebo in order to monitor the development of ADRs. We used linear mixed models to test for strain and treatment effects. We observed highly significant strain effects for almost all behavioral measurements investigated (P < 0.001). Further, we observed strong strain-by-treatment interactions for most phenotypes, particularly for changes in distance traveled, vertical activity, and extrapyramidal symptoms (EPS). Estimates of overall heritability ranged from 0.21 (change in body weight) to 0.4 (VCMs and change in distance traveled) while the portion attributable to the interactions of treatment and strain ranged from 0.01 (for change in body weight) to 0.15 (for change in EPS). Interestingly, close to 30% of RIX mice exhibited VCMs, a sensitivity to haloperidol exposure, approximately similar to the rate of TD in humans chronically exposed to haloperidol. Understanding the genetic basis for the susceptibility to antipsychotic ADRs may be possible in mouse, and extrapolation to humans could lead to safer therapeutic approaches for schizophrenia.

New findings in pharmacogenetics of schizophrenia

PURPOSE OF REVIEW

This review highlights recent advances in the investigation of genetic factors for antipsychotic response and side effects.

RECENT FINDINGS

Antipsychotics prescribed to treat psychotic symptoms are variable in efficacy and propensity for causing side effects. The major side effects include tardive dyskinesia, antipsychotic-induced weight gain (AIWG), and clozapine-induced agranulocytosis (CIA). Several promising associations of polymorphisms in genes including HSPG2, CNR1, and DPP6 with tardive dyskinesia have been reported. In particular, a functional genetic polymorphism in SLC18A2, which is a target of recently approved tardive dyskinesia medication valbenazine, was associated with tardive dyskinesia. Similarly, several consistent findings primarily from genes modulating energy homeostasis have also been reported (e.g. MC4R, HTR2C). CIA has been consistently associated with polymorphisms in the HLA genes (HLA-DQB1 and HLA-B). The association findings between glutamate system genes and antipsychotic response require additional replications.

SUMMARY

The findings to date are promising and provide us a better understanding of the development of side effects and response to antipsychotics. However, more comprehensive investigations in large, well characterized samples will bring us closer to clinically actionable findings.

Gamma-aminobutyric acid agonists for antipsychotic-induced tardive dyskinesia

BACKGROUND

Chronic antipsychotic drug treatment may cause tardive dyskinesia (TD), a long-term movement disorder. Gamma-aminobutyric acid (GABA) agonist drugs, which have intense sedative properties and may exacerbate psychotic symptoms, have been used to treat TD.

OBJECTIVES

1. Primary objectiveThe primary objective was to determine whether using non-benzodiazepine GABA agonist drugs for at least six weeks was clinically effective for the treatment of antipsychotic-induced TD in people with schizophrenia, schizoaffective disorder or other chronic mental illnesses.2. Secondary objectivesThe secondary objectives were as follows.To examine whether any improvement occurred with short periods of intervention (less than six weeks) and, if this did occur, whether this effect was maintained at longer periods of follow-up.To examine whether there was a differential effect between the various compounds.To test the hypothesis that GABA agonist drugs are most effective for a younger age group (less than 40 years old).

SEARCH METHODS

We searched the Cochrane Schizophrenia Group Trials Register (last searched April 2017), inspected references of all identified studies for further trials, and, when necessary, contacted authors of trials for additional information.

SELECTION CRITERIA

We included randomised controlled trials of non-benzodiazepine GABA agonist drugs in people with antipsychotic-induced TD and schizophrenia or other chronic mental illness.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected and critically appraised studies, extracted and analysed data on an intention-to-treat basis. Where possible and appropriate we calculated risk ratios (RRs) and their 95% confidence intervals (CIs). For continuous data we calculated mean differences (MD). We assumed that people who left early had no improvement. We contacted investigators to obtain missing information. We assessed risk of bias for included studies and created a 'Summary of findings' table using GRADE.

MAIN RESULTS

We included 11 studies that randomised 343 people. Overall, the risk of bias in the included studies was unclear, mainly due to poor reporting; allocation concealment was not described, generation of the sequence was not explicit, participants and outcome assessors were not clearly blinded. For some studies we were unsure if data were complete, and data were often poorly or selectively reported.Data from six trials showed that there may be a clinically important improvement in TD symptoms after GABA agonist treatment compared with placebo at six to eight weeks follow-up (6 RCTs, n = 258, RR 0.83, CI 0.74 to 0.92; low-quality evidence). Data from five studies showed no difference between GABA agonist treatment and placebo for deterioration of TD symptoms (5 RCTs, n = 136, RR 1.90, CI 0.70 to 5.16; very low-quality evidence). Studies reporting adverse events found a significant effect favouring placebo compared with baclofen, sodium valproate or progabide for dizziness/confusion (3 RCTs, n = 62 RR 4.54, CI 1.14 to 18.11; very low-quality evidence) and sedation/drowsiness (4 RCTS, n = 144, RR 2.29, CI 1.08 to 4.86; very low-quality evidence). Studies reporting on akathisia (RR 1.05, CI 0.32 to 3.49, 2 RCTs, 80 participants), ataxia (RR 3.25, CI 0.36 to 29.73, 2 RCTs, 95 participants), nausea/vomiting (RR 2.61, CI 0.79 to 8.67, 2 RCTs, 64 participants), loss of muscle tone (RR 3.00, CI 0.15 to 59.89, 1 RCT, 10 participants), seizures (RR 3.00, CI 0.24 to 37.67, 1 RCT, 2 participants), hypotension (RR 3.04, CI 0.33 to 28.31, 2 RCTs, 119 participants) found no significant difference between GABA drug and placebo (very low-quality evidence). Evidence on mental state also showed no effect between treatment groups (6 RCTS, n = 121, RR 2.65, CI 0.71 to 9.86; very low-quality evidence) as did data for leaving the study early (around 10% in both groups, 6 RCTS, n = 218, RR 1.47, CI 0.69 to 3.15; very low-quality evidence). No study reported on social confidence, social inclusion, social networks, or personalised quality of life, a group of outcomes selected as being of particular importance to patients.

AUTHORS' CONCLUSIONS

We are uncertain about the evidence of the effects of baclofen, progabide, sodium valproate or tetrahydroisoxazolopyridinol (THIP) for people with antipsychotic-induced TD. Evidence is inconclusive and unconvincing. The quality of data available for main outcomes ranges from very low to low. Any possible benefits are likely to be outweighed by the adverse effects associated with their use.

Genetics of tardive dyskinesia: Promising leads and ways forward

Tardive dyskinesia (TD) is a potentially irreversible and often debilitating movement disorder secondary to chronic use of dopamine receptor blocking medications. Genetic factors have been implicated in the etiology of TD. We therefore have reviewed the most promising genes associated with TD, including DRD2, DRD3, VMAT2, HSPG2, HTR2A, HTR2C, and SOD2. In addition, we present evidence supporting a role for these genes from preclinical models of TD. The current understanding of the etiogenesis of TD is discussed in the light of the recent approvals of valbenazine and deutetrabenazine, VMAT2 inhibitors, for treating TD.

Clinical risk factors for the development of tardive dyskinesia

BACKGROUND

Tardive dyskinesia (TD) is a severe condition that can affect almost 1 out of 4 patients on current or previous antipsychotic treatment, including both first-generation antipsychotics (FGAs) and second-generation antipsychotics (SGAs). While two novel vesicular monoamine transporter inhibitors, deutetrabenazine and valbenazine, have shown acute efficacy for TD, the majority of patients do not remit, and TD appears to recur once treatment is withdrawn. Hence, prevention of TD remains a crucial goal.

METHODS

We provide a clinically oriented overview of risk factors for TD, dividing them into patient-, illness- and treatment-related variables, as well as nonmodifiable and modifiable factors.

RESULTS

Unmodifiable patient-related and illness-related risk factors for TD include older age, female sex, white and African descent, longer illness duration, intellectual disability and brain damage, negative symptoms in schizophrenia, mood disorders, cognitive symptoms in mood disorders, and gene polymorphisms involving antipsychotic metabolism and dopamine functioning. Modifiable comorbidity-related and treatment-related factors include diabetes, smoking, and alcohol and substance abuse, FGA vs SGA treatment, higher cumulative and current antipsychotic dose or antipsychotic plasma levels, early parkinsonian side effects, anticholinergic co-treatment, akathisia, and emergent dyskinesia.

DISCUSSION

Clinicians using dopamine antagonists need to consider risk factors for TD to minimize TD and its consequences.

Association between genetic variation in the dopamine system and motor recovery after stroke

BACKGROUND

The dopamine system plays a key role in motor learning and neuroplasticity. Several studies have studied the efficacy of dopaminergic drugs in enhancing motor recovery after stroke, but the effects are controversial. Although genetic variations in plasticity-related genes influence each individual's capacity for recovery after stroke, limited studies have investigated the effects of polymorphism of dopamine-related genes.

OBJECTIVE

We aimed to investigate the association between motor recovery in stroke patients and polymorphisms in the dopamine-related genes catechol-O-methyltransferase (COMT), dopamine receptor D1 (DRD1), DRD2, and DRD3.

METHODS

We enrolled 74 patients with first-ever stroke (42 males, 32 females, mean age: 61.4±14.1 y). During admission, blood samples were collected, and the genotypes of COMT, DRD1, DRD2, and DRD3 were analyzed. The primary outcome was assessed with Fugl-Meyer Assessment (FMA) at 1 week, 3 months, and 6 months after stroke; secondary outcomes were assessed with Functional Independence Measure (FIM) and mini-mental state examination at 3 and 6 months after stroke. The association between polymorphisms and functional outcome was analyzed.

RESULTS

There were no significant associations between COMT polymorphisms and FMA or FIM scores at 1 week after stroke or between DRD1, DRD2, or DRD3 genotypes and FMA or FIM scores at any point. COMT genotypes were significantly associated with FMA and FIM at 3 months (p < 0.01 and p < 0.05, respectively) and at 6 months (p < 0.01 and p < 0.05, respectively).

CONCLUSION

These data suggest that genetic variation of dopamine-related genes may affect motor recovery after stroke and that COMT polymorphism could be useful for predicting motor recovery.

Pharmacogenetic tests for antipsychotic medications: clinical implications and considerations

Optimizing antipsychotic pharmacotherapy is often challenging due to significant variability in effectiveness and tolerability. Genetic factors influencing pharmacokinetics and pharmacodynamics may contribute to some of this variability. Research studies have characterized these pharmacogenetic relationships, and some genetic markers are now available as clinical tests. These advances in pharmacogenetics research and test availability have great potential to improve clinical outcomes and quality of life in psychiatric patients. For clinicians considering using pharmacogenetics, it is important to understand the clinical implications and also the limitations of markers included in currently available tests. This review focuses on pharmacokinetic and pharmacodynamic gene variants that are currently available in commercial genetic testing panels. Associations of these variants with clinical efficacy and adverse effects, as well as other clinical implications, in antipsychotic pharmacotherapy are discussed.

Cariprazine for the Treatment of Bipolar Disorder

PURPOSE

To review the data regarding a new antipsychotic, cariprazine.

CONCLUSIONS

Cariprazine is a dopamine D3, D2 partial agonist, with greater affinity to D3. It has been examined for schizophrenia, bipolar mania, bipolar depression, and unipolar depression. It has demonstrated efficacy in schizophrenia and mania, and has recently been approved by the U.S. Food and Drug Administration. However, it has a more inconsistent effect in depression, both unipolar and bipolar. Adverse effects include extrapyramidal symptoms, akathisia, and gastrointestinal distress.

PRACTICE IMPLICATIONS

Cariprazine will be a promising addition in the treatment of patients with acute mania and schizophrenia.

Pharmacogenetics of tardive dyskinesia: an updated review of the literature

Tardive dyskinesia (TD) is a serious and potentially irreversible side effect of long-term exposure to antipsychotic medication characterized by involuntary trunk, limb and orofacial muscle movements. Various mechanisms have been proposed for the etiopathophysiology of antipsychotic-induced TD in schizophrenia patients with genetic factors playing a prominent role. Earlier association studies have focused on polymorphisms in CYP2D6, dopamine-, serotonin-, GABA- and glutamate genes. This review highlights recent advances in the genetic investigation of TD. Recent promising findings were obtained with the HSPG2, DPP6, MTNR1A, SLC18A2, PIP5K2A and CNR1 genes. More research, including collection of well-characterized samples, enhancement of genome-wide strategies, gene–gene interaction and epigenetic analyses, is needed before genetic tests with clinical utility can be made available for TD.

Update on schizophrenia and bipolar disorder: focus on cariprazine

Schizophrenia and bipolar disorder are severe psychiatric disorders that are frequently associated with persistent symptoms and significant dysfunction. While there are a multitude of psychopharmacologic agents are available for treatment of these illnesses, suboptimal response and significant adverse consequences limit their utility. Cariprazine is a new, novel antipsychotic medication with dopamine D2 and D3 partial agonist effects. Its safety and efficacy have been investigated in acute psychosis of schizophrenia, bipolar mania, bipolar depression, and unipolar depression. Efficacy has been demonstrated in schizophrenia and mania. It is unclear if cariprazine is effective in depression associated with unipolar or bipolar illness. Adverse consequences include extrapyramidal symptoms including akathisia, and various gastrointestinal symptoms. The US Food and Drug Administration (FDA) has recently approved cariprazine. This review will provide clinicians with basic information regarding the research program of cariprazine.

Catechol-O-Methyltransferase Val158Met Polymorphism and Clinical Response to Antipsychotic Treatment in Schizophrenia and Schizo-Affective Disorder Patients: a Meta-Analysis

BACKGROUND

The catechol-O-methyltransferase (COMT) enzyme plays a crucial role in dopamine degradation, and the COMT Val158Met polymorphism (rs4680) is associated with significant differences in enzymatic activity and consequently dopamine concentrations in the prefrontal cortex. Multiple studies have analyzed the COMT Val158Met variant in relation to antipsychotic response. Here, we conducted a meta-analysis examining the relationship between COMT Val158Met and antipsychotic response.

METHODS

Searches using PubMed, Web of Science, and PsycInfo databases (03/01/2015) yielded 23 studies investigating COMT Val158Met variation and antipsychotic response in schizophrenia and schizo-affective disorder. Responders/nonresponders were defined using each study's original criteria. If no binary response definition was used, authors were asked to define response according to at least 30% Positive and Negative Syndrome Scale score reduction (or equivalent in other scales). Analysis was conducted under a fixed-effects model.

RESULTS

Ten studies met inclusion criteria for the meta-analysis. Five additional antipsychotic-treated samples were analyzed for Val158Met and response and included in the meta-analysis (ntotal=1416). Met/Met individuals were significantly more likely to respond than Val-carriers (P=.039, ORMet/Met=1.37, 95% CI: 1.02-1.85). Met/Met patients also experienced significantly greater improvement in positive symptoms relative to Val-carriers (P=.030, SMD=0.24, 95% CI: 0.024-0.46). Posthoc analyses on patients treated with atypical antipsychotics (n=1207) showed that Met/Met patients were significantly more likely to respond relative to Val-carriers (P=.0098, ORMet/Met=1.54, 95% CI: 1.11-2.14), while no difference was observed for typical-antipsychotic-treated patients (n=155) (P=.65).

CONCLUSIONS

Our findings suggest that the COMT Val158Met polymorphism is associated with response to antipsychotics in schizophrenia and schizo-affective disorder patients. This effect may be more pronounced for atypical antipsychotics.

Likelihood of mechanistic roles for dopaminergic, serotonergic and glutamatergic receptors in tardive dyskinesia: A comparison of genetic variants in two independent patient populations

Objectives:

An established theory for the pathogenesis of tardive dyskinesia is disturbed dopaminergic receptor sensitivity and/or dopaminergic intracellular signaling. We examined associations between genetic variants of neurotransmitter receptors and tardive dyskinesia.

Methods:

We assessed tardive dyskinesia in Caucasian psychiatric inpatients from Siberia (N = 431) and a long-stay population from the Netherlands (N = 168). These patients were genotyped for 43 tag single nucleotide polymorphisms in five neurotransmitter receptor genes, and the results for the two populations were compared.

Results:

Several significant associations with tardive dyskinesia were identified, but only GRIN2A (rs1345423) was found in both patient populations. This lack of agreement was probably due to the small effect size of the associations, the multiple testing and the small sample size of the Dutch patient population. After reviewing the literature, we propose that the constitutive stimulatory activity of serotonergic type 2 receptors may be relevant.

Conclusions:

Inactivity of the serotonergic, type 2C receptor or blockade of these receptors by atypical antipsychotic drugs may decrease the vulnerability to develop tardive dyskinesia.

Genetics and pharmacogenetics of aminergic transmitter pathways in functional gastrointestinal disorders

Functional gastrointestinal disorders (FGIDs) are highly prevalent syndromes, without evident underlying organic causes. Their pathogenesis is multifactorial in nature, with a combination of environmental and genetic factors contributing to their clinical manifestations, for which most of current treatments are not satisfactory. It is acknowledged that amine mediators (noradrenaline, dopamine and serotonin) play pivotal regulatory actions on gut functions and visceral sensation. In addition, drugs of therapeutic interest for FGIDs act on these transmitter pathways. The present article reviews current knowledge on the impact of genetics and pharmacogenetics of aminergic pathways on FGID pathophysiology, clinical presentations, symptom severity and medical management, in an attempt of highlighting the most relevant evidence and point out issues that should be addressed in future investigations.

Pharmacogenomics in psychiatry: the relevance of receptor and transporter polymorphisms

The treatment of severe mental illness, and of psychiatric disorders in general, is limited in its efficacy and tolerability. There appear to be substantial interindividual differences in response to psychiatric drug treatments that are generally far greater than the differences between individual drugs; likewise, the occurrence of adverse effects also varies profoundly between individuals. These differences are thought to reflect, at least in part, genetic variability. The action of psychiatric drugs primarily involves effects on synaptic neurotransmission; the genes for neurotransmitter receptors and transporters have provided strong candidates in pharmacogenetic research in psychiatry. This paper reviews some aspects of the pharmacogenetics of neurotransmitter receptors and transporters in the treatment of psychiatric disorders. A focus on serotonin, catecholamines and amino acid transmitter systems reflects the direction of research efforts, while relevant results from some genome-wide association studies are also presented. There are many inconsistencies, particularly between candidate gene and genome-wide association studies. However, some consistency is seen in candidate gene studies supporting established pharmacological mechanisms of antipsychotic and antidepressant response with associations of functional genetic polymorphisms in, respectively, the dopamine D2 receptor and serotonin transporter and receptors. More recently identified effects of genes related to amino acid neurotransmission on the outcome of treatment of schizophrenia, bipolar illness or depression reflect the growing understanding of the roles of glutamate and γ-aminobutyric acid dysfunction in severe mental illness. A complete understanding of psychiatric pharmacogenomics will also need to take into account epigenetic factors, such as DNA methylation, that influence individual responses to drugs.

Association of tardive dyskinesia with variation in CYP2D6: Is there a role for active metabolites?

BACKGROUND

The aim of this study was to examine whether there was an association between tardive dyskinesia (TD) and number of functional CYP2D6 genes.

METHODS

A Caucasian sample of 70 patients was recruited in 1996-1997 from South London and Maudsley National Health Service (NHS) Foundation Trust, UK. Subjects had a DSM-IIIR diagnosis of schizophrenia and were treated with typical antipsychotics at doses equivalent to at least 100 mg chlorpromazine daily for at least 12 months prior to assessment. All patients were genotyped for CYP2D6 alleles*3-5, *41, and for amplifications of the gene.

RESULTS

There were 13 patients with TD. The mean (standard deviation (SD)) years of duration of antipsychotic treatment in TD-positive was 15.8 (7.9) vs TD-negative 11.1 (7.4) (p=0.04). Increased odds of experiencing TD were associated with increased ability to metabolize CYP2D6, as measured by genotypic category (odds ratio (OR)=4.2), increasing duration in treatment (OR=1.0), and having drug-induced Parkinsonism (OR=9.7).

DISCUSSION

We found a significant association between CYP2D6 genotypic category and TD with the direction of effect being an increase in the number of functional CYP2D6 genes being associated with an increased risk of TD. This is the first study to examine the association between TD and CYP2D6 in Caucasians with this number of genotypic categories. In the future, metabolomics may be utilized in the discovery of biomarkers and novel drug targets.

Positive effects of methylphenidate on hyperactivity are moderated by monoaminergic gene variants in children with autism spectrum disorders

Methylphenidate (MPH) reduces hyperactive-impulsive symptoms common in children with autism spectrum disorders (ASDs), however, response and tolerability varies widely. We hypothesized monoaminergic gene variants may moderate MPH effects in ASD, as in typically developing children with attention-deficit/hyperactivity disorder. Genotype data were available for 64 children with ASD and hyperactivity who were exposed to MPH during a 1-week safety/tolerability lead-in phase and 58 who went on to be randomized to placebo and three doses of MPH during a 4-week blinded, crossover study. Outcome measures included the Clinical Global Impression-Improvement (CGI-I) scale and the Aberrant Behavior Checklist (ABC-hyperactivity index). A total of 14 subjects discontinued the study because of MPH side effects. Subjects were genotyped for variants in DRD1-DRD5, ADRA2A, SLC6A3, SLC6A4, MAOA and MAOB, and COMT. Forty-nine percent of the sample met positive responder criteria. In this modest but relatively homogeneous sample, significant differences by DRD1 (P=0.006), ADRA2A (P<0.02), COMT (P<0.04), DRD3 (P<0.05), DRD4 (P<0.05), SLC6A3 (P<0.05) and SLC6A4 (P<0.05) genotypes were found for responders versus non-responders. Variants in DRD2 (P<0.001) and DRD3 (P<0.04) were associated with tolerability in the 14 subjects who discontinued the trial. For this first MPH pharmacogenetic study in children with ASD, multiple monoaminergic gene variants may help explain individual differences in MPH's efficacy and tolerability.

Upregulation of dopamine D3, not D2, receptors correlates with tardive dyskinesia in a primate model

Tardive dyskinesia (TD) is a delayed and potentially irreversible motor complication arising in patients chronically exposed to centrally active dopamine D2 receptor antagonists, including antipsychotic drugs and metoclopramide. The classical dopamine D2 receptor supersensitivity hypothesis in TD, which stemmed from rodent studies, lacks strong support in humans. To investigate the neurochemical basis of TD, we chronically exposed adult capuchin monkeys to haloperidol (median, 18.5 months; n = 11) or clozapine (median, 6 months; n = 6). Six unmedicated animals were used as controls. Five haloperidol-treated animals developed mild TD movements, and no TD was observed in the clozapine group. Using receptor autoradiography, we measured striatal dopamine D1, D2, and D3 receptor levels. We also examined the D3 receptor/preprotachykinin messenger RNA (mRNA) co-expression, and quantified preproenkephalin mRNA levels, in striatal sections. Unlike clozapine, haloperidol strongly induced dopamine D3 receptor binding sites in the anterior caudate-putamen, particularly in TD animals, and binding levels positively correlated with TD intensity. Interestingly, the D3 receptor upregulation was observed in striatonigral neurons. In contrast, D2 receptor binding was comparable to controls, and dopamine D1 receptor binding was reduced in the anterior putamen. Enkephalin mRNA widely increased in all animals, but to a greater extent in TD-free animals. These results suggest for the first time that upregulated striatal D3 receptors correlate with TD in nonhuman primates, adding new insights to the dopamine receptor supersensitivity hypothesis. The D3 receptor could provide a novel target for drug intervention in human TD.

Dopamine genetic risk score predicts depressive symptoms in healthy adults and adults with depression

BACKGROUND

Depression is a common source of human disability for which etiologic insights remain limited. Although abnormalities of monoamine neurotransmission, including dopamine, are theorized to contribute to the pathophysiology of depression, evidence linking dopamine-related genes to depression has been mixed. The current study sought to address this knowledge-gap by examining whether the combined effect of dopamine polymorphisms was associated with depressive symptomatology in both healthy individuals and individuals with depression.

METHODS

Data were drawn from three independent samples: (1) a discovery sample of healthy adult participants (n = 273); (2) a replication sample of adults with depression (n = 1,267); and (3) a replication sample of healthy adult participants (n = 382). A genetic risk score was created by combining functional polymorphisms from five genes involved in synaptic dopamine availability (COMT and DAT) and dopamine receptor binding (DRD1, DRD2, DRD3).

RESULTS

In the discovery sample, the genetic risk score was associated with depressive symptomatology (β = -0.80, p = 0.003), with lower dopamine genetic risk scores (indicating lower dopaminergic neurotransmission) predicting higher levels of depression. This result was replicated with a similar genetic risk score based on imputed genetic data from adults with depression (β = -0.51, p = 0.04). Results were of similar magnitude and in the expected direction in a cohort of healthy adult participants (β = -0.86, p = 0.15).

CONCLUSIONS

Sequence variation in multiple genes regulating dopamine neurotransmission may influence depressive symptoms, in a manner that appears to be additive. Further studies are required to confirm the role of genetic variation in dopamine metabolism and depression.

BDNF Val66Met polymorphism and antipsychotic-induced tardive dyskinesia occurrence and severity: a meta-analysis

BACKGROUND

Tardive dyskinesia (TD) is a serious long-term consequence of antipsychotic treatment. Since brain-derived neurotrophic factor (BDNF) has potent neurotrophic activity, genetic alterations in the BDNF gene may affect antipsychotic-induced TD.

METHODS

Searching PubMed and Web of Science until 05/31/13, we conducted a systematic review and a meta-analysis of the effects of BDNF Val66Met polymorphism on antipsychotic-induced TD. Pooled odds ratio was calculated to assess the effects of BDNF Val66Met polymorphism on TD occurrence. Additionally, pooled standardized mean differences (Hedges' g) were calculated to assess the effects on Abnormal Involuntary Movement Scale (AIMS) total score.

RESULTS

Out of 699 potentially eligible hits, 6 studies (N=1740, mean age=46.0±10.4years; males=73.1%; Asians=80.5%, Caucasians=19.5%; schizophrenia=96.2%) were included in this meta-analysis. Pooling data from all studies, no significant associations were found between BDNF Val66Met polymorphism and TD (p=0.82) or AIMS total scores (p=0.11). However, in studies including only Caucasians (n=339), Met allele carriers had significantly higher AIMS total scores (Hedges' g=0.253, 95% confidence interval=0.030 to 0.476, p=0.026) and non-significantly higher TD occurrence (p=0.127). Conversely, there was no association between BDNF and AIMS scores (p=0.57) or TD (p=0.65) in Asians.

CONCLUSION

Although there was no significant association between BDNF Val66Met polymorphism and TD or AIMS scores across all patients, our results suggest that BDNF Val66Met polymorphism affects severity and, possibly, TD development in Caucasians. Since the number of studies and patients was still small, additional data are needed to confirm genotype-racial interactions. Furthermore, BDNF enhancing treatments for TD may require further study, especially in Caucasians.

Pharmacogenetics of antipsychotics

OBJECTIVE

During the past decades, increasing efforts have been invested in studies to unravel the influence of genetic factors on antipsychotic (AP) dosage, treatment response, and occurrence of adverse effects. These studies aimed to improve clinical care by predicting outcome of treatment with APs and thus allowing for individualized treatment strategies. We highlight most important findings obtained through both candidate gene and genome-wide association studies, including pharmacokinetic and pharmacodynamic factors.

METHODS

We reviewed studies on pharmacogenetics of AP response and adverse effects published on PubMed until early 2012. Owing to the high number of published studies, we focused our review on findings that have been replicated in independent studies or are supported by meta-analyses.

RESULTS

Most robust findings were reported for associations between polymorphisms of the cytochrome P450 system, the dopamine and the serotonin transmitter systems, and dosage, treatment response, and adverse effects, such as AP-induced weight gain or tardive dyskinesia. These associations were either detected for specific medications or for classes of APs.

CONCLUSION

First promising and robust results show that pharmacogenetics bear promise for a widespread use in future clinical practice. This will likely be achieved by developing algorithms that will include many genetic variants. However, further investigation is warranted to replicate and validate previous findings, as well as to identify new genetic variants involved in AP response and for replication of existing findings.

Pharmacogenetics of antipsychotic treatment in schizophrenia

Antipsychotics are the mainstay treatment for schizophrenia. There is large variability between individuals in their response to antipsychotics, both in efficacy and adverse effects of treatment. While the source of interindividual variability in antipsychotic response is not completely understood, genetics is a major contributing factor. The identification of pharmacogenetic markers that predict antipsychotic efficacy and adverse reactions is a growing area of research, and holds the potential to replace the current trial-and-error approach to treatment selection in schizophrenia with a personalized medicine approach.In this chapter, we provide an overview of the current state of pharmacogenetics in schizophrenia treatment. The most promising pharmacogenetic findings are presented for both antipsychotic response and commonly studied adverse reactions. The application of pharmacogenetics to schizophrenia treatment is discussed, with an emphasis on the clinical utility of pharmacogenetic testing and directions for future research.

Genetics of adverse reactions to haloperidol in a mouse diallel: a drug-placebo experiment and Bayesian causal analysis

Haloperidol is an efficacious antipsychotic drug that has serious, unpredictable motor side effects that limit its utility and cause noncompliance in many patients. Using a drug-placebo diallel of the eight founder strains of the Collaborative Cross and their F1 hybrids, we characterized aggregate effects of genetics, sex, parent of origin, and their combinations on haloperidol response. Treating matched pairs of both sexes with drug or placebo, we measured changes in the following: open field activity, inclined screen rigidity, orofacial movements, prepulse inhibition of the acoustic startle response, plasma and brain drug level measurements, and body weight. To understand the genetic architecture of haloperidol response we introduce new statistical methodology linking heritable variation with causal effect of drug treatment. Our new estimators, "difference of models" and "multiple-impute matched pairs", are motivated by the Neyman-Rubin potential outcomes framework and extend our existing Bayesian hierarchical model for the diallel (Lenarcic et al. 2012). Drug-induced rigidity after chronic treatment was affected by mainly additive genetics and parent-of-origin effects (accounting for 28% and 14.8% of the variance), with NZO/HILtJ and 129S1/SvlmJ contributions tending to increase this side effect. Locomotor activity after acute treatment, by contrast, was more affected by strain-specific inbreeding (12.8%). In addition to drug response phenotypes, we examined diallel effects on behavior before treatment and found not only effects of additive genetics (10.2-53.2%) but also strong effects of epistasis (10.64-25.2%). In particular: prepulse inhibition showed additivity and epistasis in about equal proportions (26.1% and 23.7%); there was evidence of nonreciprocal epistasis in pretreatment activity and rigidity; and we estimated a range of effects on body weight that replicate those found in our previous work. Our results provide the first quantitative description of the genetic architecture of haloperidol response in mice and indicate that additive, dominance-like inbreeding and parent-of-origin effects contribute strongly to treatment effect heterogeneity for this drug.

There is no evidence for an association between the serotonin receptor 3A gene C178T polymorphism and tardive dyskinesia in Korean schizophrenia patients

BACKGROUND

Tardive dyskinesia (TD) is a potential adverse effect of long-term treatment with antipsychotics. Previous studies have suggested a link between brain serotonergic systems and TD vulnerability. A recent report described that a serotonin 3 receptor (5-HTR3) agonist induced rhythmic movements in mice with complete paraplegia. Furthermore, it has been reported that the 5-HTR3 antagonist ondansetron is efficacious in the treatment of Gilles de la Tourette syndrome (GTS).

AIM

The aim of the present study was to determine whether the 5-HTR3A gene C178T polymorphism is associated with antipsychotic-induced TD in Korean schizophrenia patients.

METHODS

We investigated 280 Korean schizophrenia patients. Subjects with TD (n = 105) and without TD (n = 175) were matched for antipsychotic drug exposure and other relevant variables.

RESULTS

The distributions of genotypic (chi-squared = 3.55, p = 0.169) and allelic (chi-squared = 0.40, p = 0.528) frequencies did not differ between patients with and without TD. The total score on the Abnormal Involuntary Movement Scale also did not differ between the two genotype groups (F = 0.94, p = 0.391).

CONCLUSIONS

The findings of the present study do not support the involvement of the 5-HTR3A gene C178T polymorphism in TD in Korean schizophrenia subjects.

Do tardive dyskinesia and L-dopa induced dyskinesia share common genetic risk factors? An exploratory study

Tardive dyskinesia (TD) in schizophrenia patients treated with antipsychotic medications and L-dopa induced dyskinesia (LID) among Parkinson's disease (PD) affected individuals share similar clinical features. Both conditions are induced by chronic exposure to drugs that target dopaminergic receptors (antagonists in TD and agonists in LID) and cause pulsatile and nonphysiological stimulation of these receptors. We hypothesized that the two motor adverse effects partially share genetic risk factors such that certain genetic variants exert a pleiotropic effect, influencing susceptibility to TD as well as to LID. In this pilot study, we focused on 21 TD-associated SNPs, previously reported in TD genome-wide association studies or in candidate gene studies. By applying logistic regression and controlling for relevant clinical risk factors, we studied the association of the SNPs with LID vulnerability in two independent pharmacogenetic samples. We included a Jewish Israeli sample of 203 PD patients treated with L-dopa for a minimum of 3 years and evaluated the existence or absence of LID (LID+ = 128; LID- = 75). An Italian sample was composed of early LID developers (within the first 3 years of treatment, N = 187) contrasted with non-early LID developers (after 7 years or more of treatment, N = 203). None of the studied SNPs were significantly associated with LID susceptibility in the two samples. Therefore, we were unable to obtain proof of concept for our initial hypothesis of an overlapping contribution of genetic risk factors to TD and LID. Further studies in larger samples are required to reach definitive conclusions.

Genetic variation in the human brain dopamine system influences motor learning and its modulation by L-Dopa

Dopamine is important to learning and plasticity. Dopaminergic drugs are the focus of many therapies targeting the motor system, where high inter-individual differences in response are common. The current study examined the hypothesis that genetic variation in the dopamine system is associated with significant differences in motor learning, brain plasticity, and the effects of the dopamine precursor L-Dopa. Skilled motor learning and motor cortex plasticity were assessed using a randomized, double-blind, placebo-controlled, crossover design in 50 healthy adults during two study weeks, one with placebo and one with L-Dopa. The influence of five polymorphisms with established effects on dopamine neurotransmission was summed using a gene score, with higher scores corresponding to higher dopaminergic neurotransmission. Secondary hypotheses examined each polymorphism individually. While training on placebo, higher gene scores were associated with greater motor learning (p = .03). The effect of L-Dopa on learning varied with the gene score (gene score*drug interaction, p = .008): participants with lower gene scores, and thus lower endogenous dopaminergic neurotransmission, showed the largest learning improvement with L-Dopa relative to placebo (p<.0001), while L-Dopa had a detrimental effect in participants with higher gene scores (p = .01). Motor cortex plasticity, assessed via transcranial magnetic stimulation (TMS), also showed a gene score*drug interaction (p = .02). Individually, DRD2/ANKK1 genotype was significantly associated with motor learning (p = .02) and its modulation by L-Dopa (p<.0001), but not with any TMS measures. However, none of the individual polymorphisms explained the full constellation of findings associated with the gene score. These results suggest that genetic variation in the dopamine system influences learning and its modulation by L-Dopa. A polygene score explains differences in L-Dopa effects on learning and plasticity most robustly, thus identifying distinct biological phenotypes with respect to L-Dopa effects on learning and plasticity. These findings may have clinical applications in post-stroke rehabilitation or the treatment of Parkinson's disease.

Pharmacogenetics: a reality or misplaced optimism?

The paper aims to review current evidence that supports the application of genetic information in the management and use of psychotropic medication. Although the importance of an individual's genetic makeup in the metabolism of drugs has been known for at least 50 years, it is only recently that such information is finding clinical application. A literature review of recent studies suggest that there are clear variations in the way people respond to psychotropic medication. These variations can be seen across racial and ethnic lines, and are genetically determined. The hope is that, in future we will be able to use genetic information to predict which patient will benefit from which drug and at what dose. In other fields of health care such as anticoagulant therapy, the application of pharmacogenetics is now established in routine clinical care. Several psychiatric pharmacogenetic tests are currently available, including tests for the determination of metabolic status, risk of agranulocytosis and metabolic syndrome, and selection of beneficial medications. Since nurses are the centrepiece of mental health care, these advances are likely to alter significantly future mental health nurse education and practice.

Scientific challenges and implementation barriers to translation of pharmacogenomics in clinical practice

The mapping of the human genome and subsequent advancements in genetic technology had provided clinicians and scientists an understanding of the genetic basis of altered drug pharmacokinetics and pharmacodynamics, as well as some examples of applying genomic data in clinical practice. This has raised the public expectation that predicting patients' responses to drug therapy is now possible in every therapeutic area, and personalized drug therapy would come sooner than later. However, debate continues among most stakeholders involved in drug development and clinical decision-making on whether pharmacogenomic biomarkers should be used in patient assessment, as well as when and in whom to use the biomarker-based diagnostic tests. Currently, most would agree that achieving the goal of personalized therapy remains years, if not decades, away. Realistic application of genomic findings and technologies in clinical practice and drug development require addressing multiple logistics and challenges that go beyond discovery of gene variants and/or completion of prospective controlled clinical trials. The goal of personalized medicine can only be achieved when all stakeholders in the field work together, with willingness to accept occasional paradigm change in their current approach.

The role of dopamine D(3) receptors in antipsychotic activity and cognitive functions

Dopamine D(3) receptors have a pre- and postsynaptic localization in brain stem nuclei, limbic parts of the striatum, and cortex. Their widespread influence on dopamine release, on dopaminergic function, and on several other neurotransmitters makes them attractive targets for therapeutic intervention. The signaling pathways of D(3) receptors are distinct from those of other members of the D(2)-like receptor family. There is increasing evidence that D(3) receptors can form heteromers with dopamine D(1), D(2), and probably other G-protein-coupled receptors. The functional consequences remain to be characterized in more detail but might open new interesting pharmacological insight and opportunities. In terms of behavioral function, D(3) receptors are involved in cognitive, social, and motor functions, as well as in filtering and sensitization processes. Although the role of D(3) receptor blockade for alleviating positive symptoms is still unsettled, selective D(3) receptor antagonism has therapeutic features for schizophrenia and beyond as demonstrated by several animal models: improved cognitive function, emotional processing, executive function, flexibility, and social behavior. D(3) receptor antagonism seems to contribute to atypicality of clinically used antipsychotics by reducing extrapyramidal motor symptoms; has no direct influence on prolactin release; and does not cause anhedonia, weight gain, or metabolic dysfunctions. Unfortunately, clinical data with new, selective D(3) antagonists are still incomplete; their cognitive effects have only been communicated in part. In vitro, virtually all clinically used antipsychotics are not D(2)-selective but also have affinity for D(3) receptors. The exact D(3) receptor occupancies achieved in patients, particularly in cortical areas, are largely unknown, mainly because only nonselective or agonist PET tracers are currently available. It is unlikely that a degree of D(3) receptor antagonism optimal for antipsychotic and cognitive function can be achieved with existing antipsychotics. Therefore, selective D(3) antagonism represents a promising mechanism still to be fully exploited for the treatment of schizophrenia, cognitive deficits in schizophrenia, and comorbid conditions such as substance abuse.

Antipsychotic-induced movement disorders in long-stay psychiatric patients and 45 tag SNPs in 7 candidate genes: a prospective study

OBJECTIVE

Four types of antipsychotic-induced movement disorders: tardive dyskinesia (TD), parkinsonism, akathisia and tardive dystonia, subtypes of TD (orofacial and limb truncal dyskinesia), subtypes of parkinsonism (rest tremor, rigidity, and bradykinesia), as well as a principal-factor of the movement disorders and their subtypes, were examined for association with variation in 7 candidate genes (GRIN2B, GRIN2A, HSPG2, DRD3, DRD4, HTR2C, and NQO1).

METHODS

Naturalistic study of 168 white long-stay patients with chronic mental illness requiring long-term antipsychotic treatment, examined by the same rater at least two times over a 4-year period, with a mean follow-up time of 1.1 years, with validated scales for TD, parkinsonism, akathisia, and tardive dystonia. The authors genotyped 45 tag SNPs in 7 candidate genes, associated with movement disorders or schizophrenia in previous studies. Genotype and allele frequency comparisons were performed with multiple regression methods for continuous movement disorders.

RESULTS

Various tag SNPs reached nominal significance; TD with rs1345423, rs7192557, rs1650420, as well as rs11644461; orofacial dyskinesia with rs7192557, rs1650420, as well as rs4911871; limb truncal dyskinesia with rs1345423, rs7192557, rs1650420, as well as rs11866328; bradykinesia with rs2192970; akathisia with rs324035; and the principal-factor with rs10772715. After controlling for multiple testing, no significant results remained.

CONCLUSIONS

The findings suggest that selected tag SNPs are not associated with a susceptibility to movement disorders. However, as the sample size was small and previous studies show inconsistent results, definite conclusions cannot be made. Replication is needed in larger study samples, preferably in longitudinal studies which take the fluctuating course of movement disorders and gene-environment interactions into account.

Genome-wide association mapping of loci for antipsychotic-induced extrapyramidal symptoms in mice

Tardive dyskinesia (TD) is a debilitating, unpredictable, and often irreversible side effect resulting from chronic treatment with typical antipsychotic agents such as haloperidol. TD is characterized by repetitive, involuntary, purposeless movements primarily of the orofacial region. In order to investigate genetic susceptibility to TD, we used a validated mouse model for a systems genetics analysis geared toward detecting genetic predictors of TD in human patients. Phenotypic data from 27 inbred strains chronically treated with haloperidol and phenotyped for vacuous chewing movements were subject to a comprehensive genomic analysis involving 426,493 SNPs, 4,047 CNVs, brain gene expression, along with gene network and bioinformatic analysis. Our results identified ~50 genes that we expect to have high prior probabilities for association with haloperidol-induced TD, most of which have never been tested for association with human TD. Among our top candidates were genes regulating the development of brain motor control regions (Zic4 and Nkx6-1), glutamate receptors (Grin1 and Grin2a), and an indirect target of haloperidol (Drd1a) that has not been studied as well as the direct target, Drd2.

The role of pharmacogenetics in nonmalignant gastrointestinal diseases

Genetic variation influences the absorption and efflux of drugs in the intestine, the metabolism of drugs in the liver and the effects of these drugs on their target proteins. Indeed, variations in genes whose products have a role in the pathophysiology of nonmalignant gastrointestinal diseases, such as IBD, have been shown to affect the response of patients to therapy. This Review provides an overview of pharmacogenetics in the management of nonmalignant gastrointestinal diseases on the basis of data from clinical trials. Genetic variants that have the greatest effect on the management of patients with IBD involve the metabolism of thiopurines. Variation in drug metabolism by cytochrome P450 enzymes also requires attention so as to avoid drug interactions in patients receiving tricyclic antidepressants and PPIs. Few genotyping tests are currently used in the clinical management of patients with nonmalignant gastrointestinal diseases, owing to a lack of data from clinical trials showing their effectiveness in predicting nonresponse or adverse outcomes. However, pharmacogenetics could have a beneficial role in enabling pharmacotherapy for nonmalignant gastrointestinal diseases to be targeted to the individual patient.