Genetic variation analysis in parkinson disease patients with and without hallucinations: case-control study

An update on the pharmacogenetic considerations when prescribing dopamine receptor agonists for Parkinson's disease

INTRODUCTION

Parkinson's disease is a chronic neurodegenerative multisystemic disorder that affects approximately 2% of the population over 65 years old. This disorder is characterized by motor symptoms which are frequently accompanied by non-motor symptoms such as cognitive disorders. Current drug therapies aim to reduce the symptoms and increase the patient's life expectancy. Nevertheless, there is heterogeneity in therapy response in terms of efficacy and adverse effects. This wide range in response may be linked to genetic variability. Thus, it has been suggested that pharmacogenomics may help to tailor and personalize drug therapy for Parkinson's disease.

AREAS COVERED

This review describes and updates the clinical impact of genetic factors associated with the efficacy and adverse drug reactions related to common medications used to treat Parkinson's disease. Additionally, we highlight current informative recommendations for the drug treatment of Parkinson's disease.

EXPERT OPINION

The pharmacokinetic, pharmacodynamic, and safety profiles of Parkinson's disease drugs do not favor the development of pharmacogenetic tests with a high probability of success. The chances of obtaining ground-breaking pharmacogenetics biomarkers for Parkinson's disease therapy are limited. Nevertheless, additional information on the metabolism of certain drugs, and an analysis of the potential of pharmacogenetics in novel drugs could be of interest.

Pharmacogenomics-a New Frontier for Individualized Treatment of Parkinson's Disease

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disease with a significant public health burden. It is characterized by the gradual degeneration of dopamine neurons in the central nervous system. Although symptomatic pharmacological management remains the primary therapeutic method for PD, clinical experience reveals significant inter-individual heterogeneity in treatment effectiveness and adverse medication responses. The mechanisms behind the observed interindividual variability may be elucidated by investigating the role of genetic variation in human-to-human variances in medication responses and adverse effects.

OBJECTIVE

This review aims to explore the impact of gene polymorphism on the efficacy of antiparkinsonian drugs. The identification of factors associated with treatment effectiveness variability might assist the creation of a more tailored pharmacological therapy with higher efficacy, fewer side outcomes, and cheaper costs.

METHODS

In this review, we conducted a thorough search in databases such as PubMed, Web of Science, and Google Scholar, and critically examined current discoveries on Parkinson's disease pharmacogenetics. The ethnicity of the individuals, research methodologies, and potential bias of these studies were thoroughly compared, with the primary focus on consistent conclusions.

RESULTS

This review provides a summary of the existing data on PD pharmacogenetics, identifies its limitations, and offers insights that may be beneficial for future research. Previous studies have investigated the impact of gene polymorphism on the effectiveness and adverse effects of levodopa. The trendiest genes are the COMT gene, DAT gene, and DRD2 gene. However, limited study on other anti-Parkinson's drugs has been conducted.

CONCLUSION

Therefore, In order to develop an individualized precision treatment for PD, it is an inevitable trend to carry out multi-center, prospective, randomized controlled clinical trials of PD pharmacogenomics covering common clinical anti-PD drugs in large, homogeneous cohorts.

Psychosis in Parkinson's Disease: A Lesson from Genetics

Psychosis in Parkinson's disease (PDP) represents a common and debilitating condition that complicates Parkinson's disease (PD), mainly in the later stages. The spectrum of psychotic symptoms are heterogeneous, ranging from minor phenomena of mild illusions, passage hallucinations and sense of presence to severe psychosis consisting of visual hallucinations (and rarely, auditory and tactile or gustatory) and paranoid delusions. PDP is associated with increased caregiver stress, poorer quality of life for patients and carers, reduced survival and risk of institutionalization with a significant burden on the healthcare system. Although several risk factors for PDP development have been identified, such as aging, sleep disturbances, long history of PD, cognitive impairment, depression and visual disorders, the pathophysiology of psychosis in PD is complex and still insufficiently clarified. Additionally, several drugs used to treat PD can aggravate or even precipitate PDP. Herein, we reviewed and critically analyzed recent studies exploring the genetic architecture of psychosis in PD in order to further understand the pathophysiology of PDP, the risk factors as well as the most suitable therapeutic strategies.

A Systematic Review of Parkinson's Disease Pharmacogenomics: Is There Time for Translation into the Clinics?

BACKGROUND

Parkinson's disease (PD) is the second most frequent neurodegenerative disease, which creates a significant public health burden. There is a challenge for the optimization of therapies since patients not only respond differently to current treatment options but also develop different side effects to the treatment. Genetic variability in the human genome can serve as a biomarker for the metabolism, availability of drugs and stratification of patients for suitable therapies. The goal of this systematic review is to assess the current evidence for the clinical translation of pharmacogenomics in the personalization of treatment for Parkinson's disease.

METHODS

We performed a systematic search of Medline database for publications covering the topic of pharmacogenomics and genotype specific mutations in Parkinson's disease treatment, along with a manual search, and finally included a total of 116 publications in the review.

RESULTS

We analyzed 75 studies and 41 reviews published up to December of 2020. Most research is focused on levodopa pharmacogenomic properties and catechol-O-methyltransferase (COMT) enzymatic pathway polymorphisms, which have potential for clinical implementation due to changes in treatment response and side-effects. Likewise, there is some consistent evidence in the heritability of impulse control disorder via Opioid Receptor Kappa 1 (OPRK1), 5-Hydroxytryptamine Receptor 2A (HTR2a) and Dopa decarboxylase (DDC) genotypes, and hyperhomocysteinemia via the Methylenetetrahydrofolate reductase (MTHFR) gene. On the other hand, many available studies vary in design and methodology and lack in sample size, leading to inconsistent findings.

CONCLUSIONS

This systematic review demonstrated that the evidence for implementation of pharmacogenomics in clinical practice is still lacking and that further research needs to be done to enable a more personalized approach to therapy for each patient.

Clinical and Genetic Analysis of Psychosis in Parkinson's Disease

BACKGROUND

Recent studies explored polymorphisms of multiple genes as contributing to genetic susceptibility to psychosis in Parkinson's disease (PDP).

OBJECTIVE

We aimed to examine the association of seven selected polymorphisms of genes related to dopamine pathways with PDP development. At the same time, demographic and clinical correlates of PDP were assessed.

METHODS

PD patients (n = 234), treated with levodopa for at least two years, were genotyped for the rs4680 in COMT, rs6277, rs1076560, and rs2283265 in DRD2, and rs1800497 and rs2734849 polymorphisms in ANKK1 genes. Also, variable number of tandem repeats polymorphism in the DAT gene was examined. Each patient underwent comprehensive neurological examination, assessment of psychosis, as defined by the NINDS/NIMH criteria, as well as screening of depression, anxiety, and cognitive status.

RESULTS

Diagnostic criteria for PDP were met by 101 (43.2%) patients. They had longer disease duration, were taking higher doses of dopaminergic agents, and had higher scores of the motor and non-motor scales than the non-PDP group. Multivariate regression analysis revealed LEDD≥900 mg, Unified Parkinson's Disease Rating Scale III part score, the Hamilton Depression Rating Scale score≥7, the Hamilton Anxiety Rating Scale score >  14,and GG homozygotes of rs2734849 ANKK1 as independent predictors of the onset of PDP.

CONCLUSION

Besides previous exposure to dopaminergic drugs, impairment of motor status, depression and anxiety, as well-established clinical risk factors for the development of PDP, GG rs2734849 ANKK1 could also be a contributing factor, which requires addressing by future longitudinal studies.

Polymorphisms of Dopamine Receptor Genes and Parkinson's Disease: Clinical Relevance and Future Perspectives

Parkinson’s disease (PD) is a neurodegenerative disease caused by loss of dopaminergic neurons in the midbrain. PD is clinically characterized by a variety of motor and nonmotor symptoms, and treatment relies on dopaminergic replacement. Beyond a common pathological hallmark, PD patients may present differences in both clinical progression and response to drug therapy that are partly affected by genetic factors. Despite extensive knowledge on genetic variability of dopaminergic receptors (DR), few studies have addressed their relevance as possible influencers of clinical heterogeneity in PD patients. In this review, we summarized available evidence regarding the role of genetic polymorphisms in DR as possible determinants of PD development, progression and treatment response. Moreover, we examined the role of DR in the modulation of peripheral immunity, in light of the emerging role of the peripheral immune system in PD pathophysiology. A better understanding of all these aspects represents an important step towards the development of precise and personalized disease-modifying therapies for PD.

The Effect of GBA Mutations and APOE Polymorphisms on Dementia with Lewy Bodies in Ashkenazi Jews

BACKGROUND

Glucocerebrosidase (GBA) gene mutations and APOE polymorphisms are common in dementia with Lewy bodies (DLB), however their clinical impact is only partially elucidated.

OBJECTIVE

To explore the clinical impact of mutations in the GBA gene and APOE polymorphisms separately and in combination, in a cohort of Ashkenazi Jewish (AJ) patients with DLB.

METHODS

One hundred consecutively recruited AJ patients with clinically diagnosed DLB underwent genotyping for GBA mutations and APOE polymorphisms, and performed cognitive and motor clinical assessments.

RESULTS

Thirty-two (32%) patients with DLB were carriers of GBA mutations and 33 (33%) carried an APOE ɛ4 allele. GBA mutation carriers had a younger age of onset (mean [SD] age, 67.2 years [8.9] versus 71.97 [5.91]; p = 0.03), poorer cognition as assessed by the Mini-Mental State Examination (21.41 [6.9] versus 23.97 [5.18]; p < 0.005), and more severe parkinsonism as assessed with the Unified Parkinson's Disease Rating Scale motor part III (34.41 [13.49] versus 28.38 [11.21]; p = 0.01) compared to non-carriers. There were statistically significant interactions between the two genetic factors, so that patients who carried both a mild GBA mutation and the APOE ɛ4 allele (n = 9) had more severe cognitive (p = 0.048) and motor dysfunction (p = 0.037).

CONCLUSION

We found a high frequency of both GBA mutations and the APOE ɛ4 allele among AJ patients with DLB, both of which have distinct effects on the clinical disease phenotype, separately and in combination.

The role of pharmacogenomics in the personalization of Parkinson's disease treatment

Parkinson's disease (PD)-related phenotypes can vary among patients substantially, including response to dopaminergic treatment in terms of efficacy and occurrence of adverse events. Many pharmacogenetic studies have already been conducted to find genetic markers of response to dopaminergic treatment. Integration of genetic and clinical data has already resulted in construction of clinical pharmacogenetic models for prediction of adverse events. However, the results of pharmacogenetic studies are inconsistent. More comprehensive genome-wide approaches are needed to find genetic biomarkers of PD-related phenotypes to better explain the variability in response to treatment. These genetic markers should be integrated with clinical, environmental, imaging, and other omics data to build clinically useful algorithms for personalization of PD management.

The Association between DRD3 Ser9Gly Polymorphism and Depression Severity in Parkinson's Disease

More and more evidence suggests that dopamine receptor D3 gene (DRD3) plays an important role in the clinical manifestations and the treatment of Parkinson's disease (PD). DRD3 Ser9Gly polymorphism is the most frequently studied variant point. Our aim was to investigate the potential effect of DRD3 Ser9Gly polymorphism on modulating resting-state brain function and associative clinical manifestations in PD patients. We consecutively recruited 61 idiopathic PD patients and 47 healthy controls (HC) who were evaluated by clinical scales, genotyped for variant Ser9Gly in DRD3, and underwent resting-state functional magnetic resonance imaging. Based on DRD3 Ser9Gly polymorphism, PD patients and HCs were divided into four subgroups. Then, two-way analysis of covariance (ANCOVA) was applied to investigate main effects and interactions of PD and DRD3 Ser9Gly polymorphism on the brain function via amplitude of low-frequency fluctuations (ALFF) approach. The association between DRD3 Ser9Gly-modulated significantly different brain regions, and clinical manifestations were detected by Spearman's correlations. PD patients exhibited decreased ALFF values in the right inferior occipital gyrus, lingual gyrus, and fusiform gyrus. A significant difference in the interaction of “groups × genotypes” was observed in the right medial frontal gyrus. The ALFF value of the cluster showing significant interactions was positively correlated with HAMD-17 scores (r=0.489, p=0.011) and anhedonia scores (r=0.512, p=0.008) in PD patients with the Ser/Gly or Gly/Gly genotypes. Therefore, D3 gene Ser9Gly polymorphism might be associated with the severity of depression characterized by anhedonia in PD patients.

Dopaminergic Pathway Genes Influence Adverse Events Related to Dopaminergic Treatment in Parkinson's Disease

Dopaminergic pathway is the most disrupted pathway in the pathogenesis of Parkinson's disease. Several studies reported associations of dopaminergic genes with the occurrence of adverse events of dopaminergic treatment. However, none of these studies adopted a pathway based approach. The aim of this study was to comprehensively evaluate the influence of selected single nucleotide polymorphisms of key dopaminergic pathway genes on the occurrence of motor and non-motor adverse events of dopaminergic treatment in Parkinson's disease. In total, 231 Parkinson's disease patients were enrolled. Demographic and clinical data were collected. Genotyping was performed for 16 single nucleotide polymorphisms from key dopaminergic pathway genes. Logistic and Cox regression analyses were used for evaluation. Results were adjusted for significant clinical data. We observed that carriers of at least one COMT rs165815 C allele had lower odds for developing visual hallucinations (OR = 0.34; 95% CI = 0.16-0.72; p = 0.004), while carriers of at least one DRD3 rs6280 C allele and CC homozygotes had higher odds for this adverse event (OR = 1.88; 95% CI = 1.00-3.54; p = 0.049 and OR = 3.31; 95% CI = 1.37-8.03; p = 0.008, respectively). Carriers of at least one DDC rs921451 C allele and CT heterozygotes had higher odds for orthostatic hypotension (OR = 1.86; 95% CI = 1.07-3.23; p = 0.028 and OR = 2.30; 95% CI = 1.26-4.20; p = 0.007, respectively). Heterozygotes for DDC rs3837091 and SLC22A1 rs628031 AA carriers also had higher odds for orthostatic hypotension (OR = 1.94; 95% CI = 1.07-3.51; p = 0.028 and OR = 2.57; 95% CI = 1.11-5.95; p = 0.028, respectively). Carriers of the SLC22A1 rs628031 AA genotype had higher odds for peripheral edema and impulse control disorders (OR = 4.00; 95% CI = 1.62-9.88; p = 0.003 and OR = 3.16; 95% CI = 1.03-9.72; p = 0.045, respectively). Finally, heterozygotes for SLC22A1 rs628031 and carriers of at least one SLC22A1 rs628031 A allele had lower odds for dyskinesia (OR = 0.48; 95% CI = 0.24-0.98, p = 0.043 and OR = 0.48; 95% CI = 0.25-0.92; p = 0.027, respectively). Gene-gene interactions, more specifically DDC-COMT, SLC18A2-SV2C, and SLC18A2-SLC6A3, also significantly influenced the occurrence of some adverse events. Additionally, haplotypes of COMT and SLC6A3 were associated with the occurrence of visual hallucinations (AT vs. GC: OR = 0.34; 95% CI = 0.16-0.72; p = 0.005) and orthostatic hypotension (ATG vs. ACG: OR = 2.48; 95% CI: 1.01-6.07; p = 0.047), respectively. Pathway based approach allowed us to identify new potential candidates for predictive biomarkers of adverse events of dopaminergic treatment in Parkinson's disease, which could contribute to treatment personalization.

The genetic association between apolipoprotein E gene polymorphism and Parkinson disease: A meta-Analysis of 47 studies

OBJECTIVE

Although the relationship between apolipoprotein E (ApoE) gene polymorphisms and the risk of Parkinson disease (PD) has been established, the results were inconsistent and inconclusive.

METHODS

A comprehensive search examining the association between APOE polymorphisms and PD through PubMed, Embase, Chinese National Knowledge Infrastructure (CNKI), and Cochrane Library databases was performed without published year limited.

RESULTS

A total of 47 studies with 7533 cases and 14442 controls were included in present study. The results showed statistically significant association between risk factor ApoE ε4 allele and PD in Asian population (P = .003, odds ratio, OR [95% confidence interval, CI] = 1.43 [1.13,1.80]). Genotype ε2ε4 have significantly associated with PD in Asian population (P = .004, OR [95% CI] = 4.43 [1.62,12.10]). Genotype ε3ε4 was significantly associated with PD in Latin-American population (P = .01, OR [95% CI] = 1.44 [1.08,1.91]). In addition, the frequency of the genotype ε3ε4 is lower in PD group than that in the control group in Caucasian population, and the difference of genotype ε3ε4 is also statistically significant (P = .006, OR [95% CI] = 0.86 [0.77,0.96]). Although significant heterogeneity was observed among all studies, the results were shown to be stabilized by sensitive analysis. No publish bias was observed.

CONCLUSIONS

This meta-analysis suggests that the APOE ε4, but no ε2, might be a risk factor for PD in Asian population. Furthermore, the genotype ε2ε4 may be a susceptible factor for PD in Asian population, and the genotype ε3ε4 may be a susceptible factor for PD in both Caucasian and Latin-American populations.

Relationship between Apolipoprotein Superfamily and Parkinson's Disease

Objective:

Parkinson's disease (PD) is featured with motor disorder and nonmotor manifestations including psychological symptoms, autonomic nervous system dysfunction, and paresthesia, which results in great inconvenience to the patients’ life. The apolipoprotein (Apo) superfamily, as a group of potentially modifiable biomarkers in clinical practice, is of increasing significance in the diagnosis, evaluation, and prognosis of PD. The present review summarized the current understanding and emerging findings of the relationship between Apo superfamily and PD.

Data Sources:

All literatures were identified by systematically searching PubMed, Embase, and Cochrane electronic databases with terms “Parkinson disease,” “apolipoprotein,” and their synonyms until May 2017.

Study Selection:

We have thoroughly examined titles and abstracts of all the literatures that met our search strategy and the full text if the research is identified or not so definite. Reference lists of retrieved articles were also scrutinized for additional relevant studies.

Results:

The levels of plasma ApoA1 are inversely correlated with the risk of PD and the lower levels of ApoA1 trend toward association with poorer motor performance. Higher ApoD expression in neurons represents more puissant protection against PD, which is critical in delaying the neurodegeneration process of PD. It is suggested that APOE alleles are related to development and progression of cognitive decline and age of PD onset, but conclusions are not completely identical, which may be attributed to different ApoE isoforms. APOJ gene expressions are upregulated in PD patients and it is possible that high ApoJ level is an indicator of PD dementia and correlates with specific phenotypic variations in PD.

Conclusions:

The Apo superfamily has been proved to be closely involved in the initiation, progression, and prognosis of PD. Apos and their genes are of great value in predicting the susceptibility of PD and hopeful to become the target of medical intervention to prevent the onset of PD or slow down the progress. Therefore, further large-scale studies are warranted to elucidate the precise mechanisms of Apos in PD.

Genetics and Treatment Response in Parkinson's Disease: An Update on Pharmacogenetic Studies

Parkinson's disease (PD) is a complex neurodegenerative disorder characterized by a progressive loss of dopamine neurons of the central nervous system. The disease determines a significant disability due to a combination of motor symptoms such as bradykinesia, rigidity and rest tremor and non-motor symptoms such as sleep disorders, hallucinations, psychosis and compulsive behaviors. The current therapies consist in combination of drugs acting to control only the symptoms of the illness by the replacement of the dopamine lost. Although patients generally receive benefits from this symptomatic pharmacological management, they also show great variability in drug response in terms of both efficacy and adverse effects. Pharmacogenetic studies highlighted that genetic factors play a relevant influence in this drug response variability. In this review, we tried to give an overview of the recent progresses in the pharmacogenetics of PD, reporting the major genetic factors identified as involved in the response to drugs and highlighting the potential use of some of these genomic variants in the clinical practice. Many genes have been investigated and several associations have been reported especially with adverse drug reactions. However, only polymorphisms in few genes, including DRD2, COMT and SLC6A3, have been confirmed as associated in different populations and in large cohorts. The identification of genomic biomarkers involved in drug response variability represents an important step in PD treatment, opening the prospective of more personalized therapies in order to identify, for each person, the better therapy in terms of efficacy and toxicity and to improve the PD patients' quality of life.

A systematic review and integrative approach to decode the common molecular link between levodopa response and Parkinson's disease

Background

PD is a progressive neurodegenerative disorder commonly treated by levodopa. The findings from genetic studies on adverse effects (ADRs) and levodopa efficacy are mostly inconclusive. Here, we aim to identify predictive genetic biomarkers for levodopa response (LR) and determine common molecular link with disease susceptibility. A systematic review for LR was conducted for ADR, and drug efficacy, independently. All included articles were assessed for methodological quality on 14 parameters. GWAS of PD were also reviewed. Protein-protein interaction (PPI) analysis using STRING and functional enrichment using WebGestalt was performed to explore the common link between LR and PD.

Results

From 37 candidate studies on levodopa toxicity, 18 genes were found associated, of which, CA_n STR 13, 14 (DRD2) was most significantly associated with dyskinesia, followed by rs1801133 (MTHFR) with hyper-homocysteinemia, and rs474559 (HOMER1) with hallucination. Similarly, 8 studies on efficacy resulted in 4 genes in which rs28363170, rs3836790 (SLC6A3) and rs4680 (COMT), were significant. To establish the molecular connection between LR with PD, we identified 35 genes significantly associated with PD. With 19 proteins associated with LR and 35 with PD, two independent PPI networks were constructed. Among the 67 nodes (263 edges) in LR, and 62 nodes (190 edges) in PD pathophysiology, UBC, SNCA, FYN, SRC, CAMK2A, and SLC6A3 were identified as common potential candidates.

Conclusion

Our study revealed the genetically significant polymorphism concerning the ADRs and levodopa efficacy. The six common genes may be used as predictive markers for therapy optimization and as putative drug target candidates.

Electronic supplementary material

The online version of this article (10.1186/s12920-017-0291-0) contains supplementary material, which is available to authorized users.

Management of Psychosis in Parkinson's Disease: Emphasizing Clinical Subtypes and Pathophysiological Mechanisms of the Condition

Investigation into neuropsychiatric symptoms in Parkinson's disease (PD) is sparse and current drug development is mainly focused on the motor aspect of PD. The tight association of psychosis with an impaired quality of life in PD, together with an important underreporting of this comorbid condition, contributes to its actual insufficient assessment and management. Furthermore, the withdrawal from access to readily available treatment interventions is unacceptable and has an impact on PD prognosis. Despite its impact, to date no standardized guidelines to the adequate management of PD psychosis are available and they are therefore highly needed. Readily available knowledge on distinct clinical features as well as early biomarkers of psychosis in PD justifies the potential for its timely diagnosis and for early intervention strategies. Also, its specific characterisation opens up the possibility of further understanding the underlying pathophysiological mechanisms giving rise to more targeted therapeutic developments in the nearer future. A literature review on the most recent knowledge with special focus on specific clinical subtypes and pathophysiological mechanisms will not only contribute to an up to date practical approach of this condition for the health care providers, but furthermore open up new ideas for research in the near future.

Psychosis in Parkinson's Disease: Epidemiology, Pathophysiology, and Management

Psychotic symptoms are common in Parkinson's disease (PD) and are associated with poorer quality of life and increased caregiver burden. PD psychosis is correlated with several factors, such as more advanced disease, cognitive impairment, depression, and sleep disorders. The underlying causes of psychosis in PD thus involve a complex interplay between exogenous (e.g., drugs, intercurrent illnesses) and endogenous (e.g., PD disease pathology) factors. Current theories of the pathophysiology of PD psychosis have come from several neuropathological and neuroimaging studies that implicate pathways involving visual processing and executive function, including temporo-limbic structures and neocortical gray matter with altered neurotransmitter functioning (e.g., dopamine, serotonin, and acetylcholine). Treatment of PD psychosis requires a step-wise process, including initial careful investigation of treatable triggering conditions and a comprehensive evaluation with adjustment of PD medications and/or initiation of specific antipsychotic therapies. Clozapine remains the only recommended drug for the treatment of PD psychosis; however, because of regular blood monitoring, quetiapine is usually first-line therapy, although less efficacious. Emerging studies have focused on agents involving other neurotransmitters, including the serotonin 5-HT2A receptor inverse agonist pimavanserin, cholinesterase inhibitors, and antidepressants and anxiolytics.

The psychosis spectrum in Parkinson disease

In 2007, the clinical and research profile of illusions, hallucinations, delusions and related symptoms in Parkinson disease (PD) was raised with the publication of a consensus definition of PD psychosis. Symptoms that were previously deemed benign and clinically insignificant were incorporated into a continuum of severity, leading to the rapid expansion of literature focusing on clinical aspects, mechanisms and treatment. Here, we review this literature and the evolving view of PD psychosis. Key topics include the prospective risk of dementia in individuals with PD psychosis, and the causal and modifying effects of PD medication. We discuss recent developments, including recognition of an increase in the prevalence of psychosis with disease duration, addition of new visual symptoms to the psychosis continuum, and identification of frontal executive, visual perceptual and memory dysfunction at different disease stages. In addition, we highlight novel risk factors - for example, autonomic dysfunction - that have emerged from prospective studies, structural MRI evidence of frontal, parietal, occipital and hippocampal involvement, and approval of pimavanserin for the treatment of PD psychosis. The accumulating evidence raises novel questions and directions for future research to explore the clinical management and biomarker potential of PD psychosis.

Polymorphisms of Dopamine Receptor Genes and Risk of L-Dopa-Induced Dyskinesia in Parkinson's Disease

L-dopa–induced dyskinesia (LID) is a frequent motor complication of Parkinson’s disease (PD), associated with a negative prognosis. Previous studies showed an association between dopamine receptor (DR) gene (DR) variants and LID, the results of which have not been confirmed. The present study is aimed to determine whether genetic differences of DR are associated with LID in a small but well-characterized cohort of PD patients. To this end we enrolled 100 PD subjects, 50 with and 50 without LID, matched for age, gender, disease duration and dopaminergic medication in a case-control study. We conducted polymerase chain reaction for single nucleotide polymorphisms (SNP) in both D1-like (DRD1A48G; DRD1C62T and DRD5T798C) and D2-like DR (DRD2G2137A, DRD2C957T, DRD3G25A, DRD3G712C, DRD4C616G and DRD4nR VNTR 48bp) analyzed genomic DNA. Our results showed that PD patients carrying allele A at DRD3G3127A had an increased risk of LID (OR 4.9; 95% CI 1.7–13.9; p = 0.004). The present findings may provide valuable information for personalizing pharmacological therapy in PD patients.

Pharmacogenetics of Parkinson's Disease in Clinical Practice

Background

Pharmacogenetics aims to identify the genetic factors participating in the heterogeneity of drug response. The ultimate goal is to provide personalized treatment by identifying responders and non-responders, individuals at risk of developing drug adverse effects, and by adjusting dosage. Several studies have been performed in Parkinson's disease (PD), to investigate drug response variability according to genetic factors for dopamine replacement therapies.

Methods

We performed a systematic literature search of articles related to pharmacogenetic studies in PD, and found 47 studies.

Findings

Motor response and adverse reactions to dopaminergic drugs were associated with genes encoding enzymes of their metabolism as well as their receptors or targets. Despite some interesting results, considerable work remains to be done to replicate and validate their clinical relevance before translation into clinical practice.

Conclusions

There are currently no guidelines published for pharmacogenetic factors related to PD drugs. More research is need in this field in order to improve our knowledge in drug response variability in PD. Algorithms taking into account clinical, pharmacological, and genetic factors are probably the most promising way to help for a personalized medicine in PD.

Transcriptome Profile Changes in Mice with MPTP-Induced Early Stages of Parkinson's Disease

Parkinson's disease (PD) is one of the most common neurodegenerative diseases. Despite progress in the study of the molecular, genetic, and pathogenic mechanisms of PD, it is unclear which processes trigger the development of the pathology associated with PD. Models of the presymptomatic and early symptomatic stages of PD induced by MPTP have been used to analyze changes in transcriptome profile in brain tissues, to identify specific patterns and mechanisms underlying neurodegeneration in PD. The whole-transcriptome analysis in the brain tissues of the mice with MPTP-induced PD showed that striatum is involved in the pathogenesis in the earliest stages and the processes associated with vesicular transport may be altered. The expression profiles of the genes studied in the substantia nigra and peripheral blood confirm that lymphocytes from peripheral blood may reflect processes occurring in the brain. These data suggest that messenger RNA (mRNA) levels in peripheral blood may provide potential biomarkers of the neurodegeneration occurring in PD. The changes in expression at the mRNA and protein levels suggest that Snca may be involved in neurodegeneration and Drd2 may participate in the development of the compensatory mechanisms in the early stages of PD pathogenesis. Our data suggest that the brain cortex may be involved in the pathological processes in the early stages of PD, including the presymptomatic stage.

Polymorphisms of dopamine receptor genes and risk of visual hallucinations in Parkinson's patients

BACKGROUND

Visual hallucinations (VHs) are frequent non-motor complication of Parkinson's disease (PD), associated to a negative prognosis. Previous studies showed an association between dopamine receptor (DR) gene (DR) variants and psychosis in Alzheimer's disease, addictions, schizophrenia, and bipolar disorder. However, there are only a few studies on DR variants and VHs in PD, which did not provide conclusive results.

OBJECTIVES

The present study aimed to determine whether genetic differences of DR are associated with visual hallucinations (VHs) in a cohort of Parkinson's disease (PD) patients.

METHODS

A case-control study of 84 PD subjects, 42 with and 42 without VHs,that were matched for age, gender, disease duration, and dopaminergic medication was conducted. Polymerase chain reaction for SNPs in both D1-like (DRD1A-48G [rs4532] and C62T [rs686], DRD5T798C [rs6283]) and D2-like DR (DRD2G2137A [rs1800497] and C957T [rs6277], DRD3G25A [rs6280] and G712C [rs1800828], DRD4C616G [rs747302] and nR VNTR 48bp) analyzed genomic DNA.

RESULTS

Patients carrying allele T at DRD1C62T had an increased risk of VHs, expressed as OR (95 % CI, p value), of 10.7 (2.9-40, p = 0.0001). Moreover, patients with DRD1-48 GG and 62TT genotype displayed shorter time to VHs, whereas a longer time to VHs was found in subjects carrying the DRD4 CG alleles.

CONCLUSIONS

PD patients with VHs display higher frequency of DR SNPs associated with increased D1-like activity and decreased D2-like activity. Our data are in line with associations reported in other neurodegenerative and psychiatric conditions. Results likely provide valuable information for personalizing pharmacological therapy in PD patients.

How close are we to individualized medicine for Parkinson's disease?

INTRODUCTION

There is a considerable inter-individual heterogeneity in clinical features, disease course, and treatment response in Parkinson's disease (PD), which can be explained not only by disease process and clinical variables, but also by an impact from genetic factors. Evidence-based medicine relies on large randomized control trials and meta-analysis-average medicine, which ignores individual differences. However, we are now in the early phases of a paradigm shift in medicine relating to individuality and variability. The purpose of individualized medicine is to predict patients' responses to targeted therapy using diagnostic tests based on genetics or other molecular mechanisms, thus providing the right drug at the right dose at the right time.

AREAS COVERED

In this article, we outline current state of individualized medicine for PD. Expert Commentary: Pharmacogenomics, an important element of individualized medicine, is just beginning to be considered in PD. To advance the clinical use of pharmacogenomics, big data cohort for genomic research and multidisciplinary team approaches are necessary.

Genetic substrates of psychosis in patients with Parkinson's disease: A critical review

Patients with Parkinson's disease (PD) may develop several non-motor symptoms such as psychosis, depression, cognitive impairment, autonomic disturbances and sleep disturbances. Psychosis is one of the common non-motor symptoms, which commonly manifests as visual hallucinations and minor hallucinations such as sense of passage and presence. Though long-term dopaminergic therapy, longer duration of PD and cognitive impairment have been described as risk factors for emergence of psychosis in PD, predicting psychosis in PD remains challenging. Multiple studies have explored the genetic basis of psychosis in PD by studying polymorphisms of several genes. Most of the studies have focused on apolipoprotein E polymorphism followed by polymorphisms in cholecystokinin (CCK) system, dopamine receptors and transporters, HOMER gene, serotonin, catechol-o-methyltransferase, angiotensin converting enzyme and tau. Other than the studies on polymorphisms of CCK, most of the studies have reported conflicting results regarding association with psychosis in PD. Three out of four studies on CCK polymorphism have reported significant association of -45C>T polymorphism with the presence of hallucinations. The discrepancies in the results across the studies reviewed are possibly due to racial differences as well as differences in the patient characteristics. This review critically analyzes the published studies on genetic polymorphisms in patients with PD and psychosis.

Psychiatric Conditions in Parkinson Disease: A Comparison With Classical Psychiatric Disorders

Psychiatric conditions often complicate the outcome of patients affected by Parkinson disease (PD), but they differ from classical psychiatric disorders in terms of underlying biological mechanisms, clinical presentation, and treatment response. The purpose of the present review is to illustrate the biological and clinical aspects of psychiatric conditions associated with PD, with particular reference to the differences with respect to classical psychiatric disorders. A careful search of articles on main databases was performed in order to obtain a comprehensive review about the main psychiatric conditions associated with PD. A manual selection of the articles was then performed in order to consider only those articles that concerned with the topic of the review. Psychiatric conditions in patients with PD present substantial differences with respect to classical psychiatric disorders. Their clinical presentation does not align with the symptom profiles represented by Diagnostic and Statistical Manual for Mental Disorders and International Classification of Diseases. Furthermore, psychiatry treatment guidelines are of poor help in managing psychiatric symptoms of patients with PD. Specific diagnostic tools and treatment guidelines are needed to allow early diagnosis and adequate treatment of psychiatric conditions in comorbidity with PD.

Clinical implications of neuropharmacogenetics

INTRODUCTION

Pharmacogenetics aims to identify the underlying genetic factors participating in the variability of drug response. Indeed, genetic variability at the DNA or RNA levels can directly or indirectly modify the pharmacokinetic or the pharmacodynamic parameters of a drug. The ultimate aim of pharmacogenetics is to move towards a personalised medicine by predicting responders and non-responders, adjusting the dose of the treatment, and identifying individuals at risk of adverse drug effects.

METHODS

A literature research was performed in which we reviewed all pharmacogenetic studies in neurological disorders including neurodegenerative diseases, multiple sclerosis, stroke and epilepsy.

RESULTS

Several pharmacogenetic studies have been performed in neurology, bringing insights into the inter-individual drug response variability and in the pathophysiology of neurological diseases. The principal implications of these studies for the management of patients in clinical practice are discussed.

CONCLUSION/DISCUSSION

Although several genetic factors have been identified in the modification of drug response in neurological disorders, most of them have a marginal predictive effect at the single gene level, suggesting mutagenic interactions as well as other factors related to drug interaction and disease subtypes. Most pharmacogenetic studies deserve further replication in independent populations and, ideally, in pharmacogenetic clinical trials to demonstrate their relevance in clinical practice.

Parkinson's disease pharmacogenomics: new findings and perspectives

Parkinson's disease (PD) is unique among neurodegenerative disorders because a highly effective pharmacological symptomatic treatment is available. The marked variability in drug response and in adverse profiles associated with this treatment led to the search of genetic markers associated with these features. We present a review of the literature on PD pharmacogenetics to provide a critical discussion of the current findings, new approaches, limitations and recommendations for future research. Pharmacogenetics studies in this field have assessed several outcomes and genes, with special focus on dopaminergic genes, mainly DRD2, which is the most important receptor in nigrostriatal pathway. The heterogeneity in methodological strategies employed by different studies is impressive. The question of whether PD pharmacogenetics studies will improve clinical management by causing a shift from a trial-and-error approach to a pharmacological regimen that takes into account the individual variability remains an open question. Collaborative longitudinal studies with larger sample sizes, better outcome definitions and replication studies are required.

[Parkinson's disease and psychoses]

Psychotic symptoms are common in Parkinson's disease (PD) and are associated with increased disability, worsened quality of life, and poor long-term prognosis. In this article, clinical features, hypotheses on pathogenesis, and current treatment strategies for Parkinson's disease psychosis (PDP) are reviewed. According to epidemiological studies, the prevalence of PDP is between 20 to 40 %. Complex visual hallucinations are the most common psychotic symptoms and are present in 17-72 % of the patients. Other sensory disturbances encompass tactile hallucinations and minor hallucinatory phenomena, such as sense of presence and visual illusions. Hallucinations are often accompanied by delusions, whose most frequent themes are persecution and jealousy. The pathophysiology of PDP remains unclear. Different factors have been implicated, including Levo-dopa and dopaminergic medications, neurotransmitter imbalances, neuroanatomic alterations, abnormal visuospatial processes, and genetic predisposition. The first-line strategy in the treatment of persistent and problematic PDP is represented by reduction in anti-PD medications. Second-generation antipsychotics are the treatment of choice, with clozapine being demonstrated as the most effective and tolerable drug for PD patients.

Behavioral effects of levodopa

In recent years, levodopa-induced behavioral changes have received increased attention in the medical literature and in clinical practice. The spectrum of these symptoms includes non-motor fluctuations with neuropsychiatric symptoms, compulsive behaviors such as punding, dopamine dysregulation syndrome, and impulse control disorders, psychosis and hallucinations, as well as hypomania and mania. Despite knowledge of the clinical features associated with these behaviors, many of them are probably underdiagnosed. Although the mechanisms underlying behavioral symptoms are still incompletely understood, recent data from imaging and pathological studies have increased our understanding and guided new treatment strategies. Appropriate management remains challenging, because reduction of levodopa (l-dopa) and dopaminergic treatment is often recommended; however, doses required for control of motor symptoms may still induce behavioral changes. Newer modes of delivery of dopaminergic treatment, deep brain stimulation, and nondopaminergic agents may either provide alternatives for treatment of these behavioral problems or permit treatment of parkinsonism with less risk of these behavioral disorders.

Trigger medications and patient-related risk factors for Parkinson disease psychosis requiring anti-psychotic drugs: a retrospective cohort study

Background

Psychoses such as hallucinations are a frequent non-motor problem in patients with Parkinson disease (PD) and serious psychosis requires anti-psychotic medications that worsen Parkinsonism. Although psychosis could be associated with patient-related or biological factors such as cognition, age, and severity of PD, it can also be associated with medications.

Therefore we aimed to investigate patient-related and medication-related risks of psychosis requiring anti-psychotic medications (serious psychosis).

Methods

A retrospective cohort of 331 PD patients was followed for 2 years. Patient-related factors associated with risk of psychosis were identified by a survival time analysis. In patients who developed psychosis, medications during the hazard period (1-14 days before psychosis) were contrasted with those during the control periods (1 and 3 months before psychosis) using a case–crossover analysis to identify medication-related risks of psychosis.

Results

Serious psychosis was detected in 52 patients and the incidence was estimated to be 116 (95% confidence interval [CI], 85-148) per 1,000 person-years. Analyses of baseline characteristics revealed the risk to be higher in patients with a modified Hoehn–Yahr stage of ≥4 (hazard ratio [HR], 2.22; 95% CI, 1.11-4.40), those with a longer duration of PD (HR, 1.25; 95% CI, 1.00-1.55, per 5 years) and those with Mini-Mental State Examination scores of ≤24 (HR, 2.66; 95% CI, 1.37-5.16). The case-crossover analysis revealed that anti-cholinergics use (HR, 19.7; 95% CI, 2.39-162) elevated the risk, while donepezil use reduced it (HR, 0.48; 95% CI, 0.27-0.85).

Conclusions

Risk of psychosis was elevated by increasing severity of PD, cognitive dysfunction and duration of the disease. It was elevated by use of anti-cholinergic drugs and reduced by use of donepezil. The medication-related risk was higher in patients aged ≥ 70 years. In contrast, there was no significant medication-related risk in younger patients, suggesting different pathomechanisms between young and old patients.

Cerebral correlates of psychotic syndromes in neurodegenerative diseases

Psychosis has been recognized as a common feature in neurodegenerative diseases and a core feature of dementia that worsens most clinical courses. It includes hallucinations, delusions including paranoia, aggressive behaviour, apathy and other psychotic phenomena that occur in a wide range of degenerative disorders including Alzheimer's disease, synucleinopathies (Parkinson's disease, dementia with Lewy bodies), Huntington's disease, frontotemporal degenerations, motoneuron and prion diseases. Many of these psychiatric manifestations may be early expressions of cognitive impairment, but often there is a dissociation between psychotic/behavioural symptoms and the rather linear decline in cognitive function, suggesting independent pathophysiological mechanisms. Strictly neuropathological explanations are likely to be insufficient to explain them, and a large group of heterogeneous factors (environmental, neurochemical changes, genetic factors, etc.) may influence their pathogenesis. Clinico-pathological evaluation of behavioural and psychotic symptoms (PS) in the setting of neurodegenerative and dementing disorders presents a significant challenge for modern neurosciences. Recognition and understanding of these manifestations may lead to the development of more effective preventive and therapeutic options that can serve to delay long-term progression of these devastating disorders and improve the patients' quality of life. A better understanding of the pathophysiology and distinctive pathological features underlying the development of PS in neurodegenerative diseases may provide important insights into psychotic processes in general.

Pharmacogenomics in neurology: current state and future steps

In neurology, as in any other clinical specialty, there is a need to develop treatment strategies that allow stratification of therapies to optimize efficacy and minimize toxicity. Pharmacogenomics is one such method for therapy optimization: it aims to elucidate the relationship between human genome sequence variation and differential drug responses. Approaches have focused on candidate approaches investigating absorption-, distribution-, metabolism, and elimination (ADME)-related genes (pharmacokinetic pathways), and potential drug targets (pharmacodynamic pathways). To date, however, only few genetic variants have been incorporated into clinical algorithms. Unfortunately, a large number of studies have thrown up contradictory results due to a number of deficiencies, including small sample sizes, inadequate phenotyping, and genotyping strategies. Thus, there still exists an urgent need to establish biomarkers that could help to select for patients with an optimal benefit to risk relationship. Here we review recent advances, and limitations, in pharmacogenomics for agents used in neuroimmunology, neurodegenerative diseases, ischemic stroke, epilepsy, and primary headaches. Further work is still required in all of these areas, which really needs to progress on several fronts, including better standardized phenotyping, appropriate sample sizes through multicenter collaborations and judicious use of new technological advances such as genome-wide approaches, next generation sequencing and systems biology. In time, this is likely to lead to improvements in the benefit-harm balance of neurological therapies, cost efficiency, and identification of new drugs.

An update expert opinion on management and research strategies in Parkinson's disease psychosis

INTRODUCTION

Psychosis, a frequent complication in Parkinson's disease (PD), contributes significantly to morbidity, mortality, nursing-home placement and quality of life. Medication side effects, issues of trial design and negative outcomes have limited clinical advances of new treatments for PD psychosis. Evidence-based medicine maintains clozapine as the most effective antipsychotic in PD without motor worsening, despite risk of agranulocytosis. Safe, effective treatments that improve psychosis without exacerbating parkinsonism are urgently needed.

AREAS COVERED

This article reviews the: i) phenomenology of PD psychosis, ii) pharmacological rationale for antipsychotics in PD; iii) clinical trials of antipsychotics in PD; iv) novel research strategies such as neuroimaging, genetics and animal models; and v) associated challenges in studying and treating PD psychosis. Preparation of this review included an extensive literature search using PubMed.

EXPERT OPINION

Management of PD psychosis is complex. Challenges pertaining to study design, rating scales, subject recruitment and completion have limited PD psychosis treatment trials. Novel research strategies focus on nondopaminergic systems and incorporate neuroimaging, genetic associations and animal models. These strategies also have challenges but have the potential to enhance our understanding of PD psychosis and advance the development of agents that can ultimately be tested in well-designed, randomized, controlled trials.

New thoughts on thought disorders in Parkinson's disease: review of current research strategies and challenges

Psychosis is a frequent nonmotor complication in Parkinson's disease (PD), characterized by a broad phenomenology and likely due to a variety of intrinsic (i.e., PD-related) and extrinsic factors. Safe and effective therapies are greatly needed as PD psychosis contributes significantly to morbidity, mortality, nursing home placement, and quality of life. Novel research strategies focused on understanding the pharmacology and pathophysiology of PD psychosis, utilizing translational research including animal models, genetics, and neuroimaging, and even looking beyond the dopamine system may further therapeutic advances. This review discusses new research strategies regarding the neurobiology and treatment of PD psychosis and several associated challenges.

Nonmotor symptoms in Parkinson’s disease: the dark side of the moon

Nonmotor symptoms may appear during the course of Parkinson’s disease, complicating the advanced phase in particular, but are also common in the premotor phase of Parkinson’s disease. The appearance of nonmotor manifestations represents a milestone, determining a worse prognosis and lower quality of life; however, they are often misdiagnosed and untreated. The spectrum of nonmotor symptoms encompasses mood disorders, psychosis, dementia, sleep disorders, impulse-control disorders and autonomic dysfunctions. This article describes these nonmotor symptoms and their management.

Epidemiology of psychosis in Parkinson's disease

Psychotic symptoms are frequent and disabling in patients with Parkinson's disease (PD). Methodological issues in the epidemiology of PD associated psychosis (PDP) include differences in the symptoms assessed, the methods of assessment, and the selection of patients. Most studies are prospective clinic-based cross-sectional studies providing point prevalence rates in samples on dopaminergic treatment. Visual hallucinations are present in about one quarter to one third of the patients, auditory in up to 20%. Tactile/somatic, and olfactory hallucinations are usually not systematically sought. Minor phenomena such as sense of presence and visual illusions affect 17 to 72% of the patients, and delusions about 5%. Lifetime prevalence of visual hallucinations reaches approximately 50%. Prospective longitudinal cohort studies suggest that hallucinations persist and worsen in individual patients, and that their prevalence increases with time. A facilitating role of treatment on PDP is demonstrated at least for dopaminergic agonists, but there is no simple dose-effect relationship between dopaminergic treatment and the presence or severity of hallucinations. The main endogenous non-modifiable risk factor is cognitive impairment. Other associated factors include older age/longer duration of PD, disease severity, altered dream phenomena, daytime somnolence, and possibly depression and dysautonomia. PDP reduces quality of life in patients and increases caregiver distress, and is an independent risk factor for nursing home placement and development of dementia.

Hallucinations in Parkinson disease

Patients with Parkinson disease (PD) can experience hallucinations (spontaneous aberrant perceptions) and illusions (misinterpretations of real perceptual stimuli). Of such phenomena, visual hallucinations (VHs) and illusions are the most frequently encountered, although auditory, olfactory and tactile hallucinations can also occur. In cross-sectional studies, VHs occur in approximately one-third of patients, but up to three-quarters of patients might develop VHs during a 20-year period. Hallucinations can have substantial psychosocial effects and, historically, were the main reason for placing patients in nursing homes. Concomitant or overlapping mechanisms are probably active during VHs, and these include the following: central dopaminergic overactivity and an imbalance with cholinergic neurotransmission; dysfunction of the visual pathways, including specific PD-associated retinopathy and functional alterations of the extrastriate visual pathways; alterations of brainstem sleep-wake and dream regulation; and impaired attentional focus. Possible treatments include patient-initiated coping strategies, a reduction of antiparkinson medications, atypical neuroleptics and, potentially, cholinesterase inhibitors. Evidence-based studies, however, only support the use of one atypical neuroleptic, clozapine, and only in patients without dementia. Better phenomenological discrimination, combined with neuroimaging tools, should refine therapeutic options and improve prognosis. The aim of this Review is to present epidemiological, phenomenological, pathophysiological and therapeutic aspects of hallucinations in PD.

Genetic polymorphism of Angiotensin-Converting Enzyme is not associated with the development of Parkinson's disease and of L-dopa-induced adverse effects

Sporadic Parkinson's disease (PD) is a frequent neurodegenerative movement disorder. Both environmental and genetic factors have been studied in the etiology of PD. Among genetic factors, increasing evidences suggest that deletion/insertion (D/I) gene polymorphism of the angiotensin I-converting enzyme (ACE) may be involved in the pathogenesis of PD and in the occurrence of the adverse effects of chronic L-dopa therapy. We investigated this hypothesis by evaluating the frequency of the ACE gene D/I polymorphism in 120 Italian PD patients and 132 controls. Out of the 120 PD patients, 91 were under chronic L-dopa treatment. Our results revealed no difference in ACE I/D genotype (chi(2)=0.79, p=0.66) and allele (chi(2)=0.34, p=0.56) frequencies between PD and controls. We also failed to observe any significant association with the occurrence of L-dopa-induced adverse effects in long-term treated PD patients, thereby excluding the presence of an association between ACE I/D genotypes and the genetic susceptibility to PD and the development of adverse effect of chronic L-dopa therapy.

Cognitive and behavioural impairment in Parkinson's disease

Although Parkinson's disease (PD) has been considered to primarily affect motor abilities, increasing emphasis is being placed on cognitive and behavioural impairment in this disorder. Depression, dementia, psychosis and impulse control disorders have a major impact on quality of life for both patients and families. This article reviews cognitive and behavioural disturbances in PD and their relation to affective and motor symptoms, treatment of dementia associated with PD, and treatment approaches to psychosis in PD. We also discuss similarities between the dementia of PD and dementia with Lewy bodies.

The safety of dopamine agonists in the treatment of Parkinson's disease

Dopamine agonists are highly effective as adjunctive therapy to levodopa in advanced Parkinson's disease. These drugs have rapidly gained popularity as a monotherapy in the early stages of Parkinson's disease for patients < 65-70 years old, because they are about as effective as levodopa, but patients demonstrate a lower tendency to develop motor complications. However, dopamine agonists could have peripheral and central side effects, which are often the reason for the discontinuation of the treatment. This review focuses on the potential negative effects related to the use of dopamine agonists in the treatment of Parkinson's disease.

Psychosis in Parkinson's disease: phenomenology, frequency, risk factors, and current understanding of pathophysiologic mechanisms

Psychosis in Parkinson's disease refers to a combination of hallucinations and delusions occurring with a clear sensorium and a chronic course. Hallucinations may involve several sensory modalities. Complex visual hallucinations are the most common type. "Minor" hallucinatory phenomena are frequently present and include visual illusions, passage hallucinations, and sense of presence. Insight may be lost in patients with cognitive impairment. Delusions of a paranoid type are more rare than hallucinations. Both hallucinations and delusions are more frequent in Parkinson's disease patients with dementia. Pathogenesis involves complex and probably multifactorial mechanisms, including pharmacologic (dopaminergic treatment and others) and disease-related factors.

New approaches to understanding hallucinations in Parkinson's disease: phenomenology and possible origins

The authors review current literature on hallucinations in Parkinson's disease (PD). Recent neuropathological studies showed that hallucinations occur in synucleinopathies and are a significant predictor of Lewy Body depositions. Therefore, hallucinations are a hallmark of PD and of dementia with Lewy Bodies. Visual hallucinations are mostly complex and kinematic; preserved or disturbed insight on the nature of hallucinations is a major prognostic factor, although eventually all hallucinators will present with reduced insight. Current theories on the origin of hallucinations point to visual dysfunction, dream overflow and cognitive impairment, yet objection can be raised on each one of the putative models of hallucinations. Understanding of the origin of hallucinations is required in order to develop treatments: all treatment evaluations were focused in general on psychosis, and only clozapine obtained positive evidence-based ratings on efficacy. However, it is likely that cholinesterase inhibitors, antipsychotics and anti-5-hydroxytryptamine(3) agents and drugs acting on sleep regulation will have different and perhaps opposite effects on different types of hallucinations, whether they are accompanied by disturbed insight, sleep disorders or other psychotic features. Further studies will try to separate phenomenology and responses to treatment and will investigate the relevance of concomitant sleep disorders and abnormality of frontoparietal networks involved in the attention process.

Pathophysiology and treatment of psychosis in Parkinson's disease: a review

Psychotic symptoms in Parkinson's disease (PD) are relatively common and, in addition to creating a disturbance in patients' daily lives, have consistently been shown to be associated with poor outcome. Our understanding of the pathophysiology of psychosis in PD has expanded dramatically over the past 15 years, from an initial interpretation of symptoms as dopaminergic drug adverse effects to the current view of a complex interplay of extrinsic and disease-related factors.PD psychosis has unique clinical features, namely that it arises within a context of a clear sensorium and retained insight, there is relative prominence of visual hallucinations and progression occurs over time. PD psychosis tends to emerge later in the disease course, and disease duration represents one risk factor for its development. The use of anti-PD medications (particularly dopamine receptor agonists) has been the most widely identified risk factor for PD psychosis. Other risk factors discussed in the literature include older age, disease severity, sleep disturbance, cognitive impairment, dementia and/or depression.Recent efforts have aimed to explore the complex pathophysiology of PD psychosis, which is now known to involve an interaction between extrinsic, drug-related and intrinsic, disease-related components. The most important extrinsic factor is use of dopaminergic medication, which plays a prominent role in PD psychosis. Intrinsic factors include visual processing deficits (e.g. lower visual acuity, colour and contrast recognition deficits, ocular pathology and functional brain abnormalities identified amongst hallucinating PD patients); sleep dysregulation (e.g. sleep fragmentation and altered dream phenomena); neurochemical (dopamine, serotonin, acetylcholine, etc.) and structural abnormalities involving site-specific Lewy body deposition; and genetics (e.g. apolipoprotein E epsilon4 allele and tau H1H1 genotype). Preliminary reports have also shown a potential relationship between deep brain stimulation surgery and PD psychosis.When reduction in anti-PD medications to the lowest tolerated dose does not improve psychosis, further intervention may be warranted. Several atypical antipsychotic agents (i.e. clozapine, olanzapine) have been shown to be efficacious in reducing psychotic symptoms in PD; however, use of clozapine requires cumbersome monitoring and olanzapine leads to motor worsening. Studies of ziprasidone and aripiprazole are limited to open-label trials and case reports and are highly variable; however, it appears that while each may be effective in some patients, both are associated with adverse effects. While quetiapine has not been determined efficacious in two randomized controlled trials, it is a common first-line treatment for PD psychosis because of its tolerability, ease of use and demonstrated utility in numerous open-label reports. Cholinesterase inhibitors currently represent the most promising pharmacological alternative to antipsychotics. Tacrine is rarely tried because of hepatic toxicity, and controlled trials with donepezil have not shown significant reductions in psychotic symptoms, due perhaps to methodological limitations. However, results from an open-label study and a double-blind, placebo-controlled trial involving 188 hallucinating PD patients support the efficacy of rivastigmine. With regard to non-pharmacological interventions, case reports suggest that electroconvulsive therapy has the potential to reduce psychotic symptoms and may be considered in cases involving concurrent depression and/or medication-refractory psychosis. Limited case reports also suggest that specific antidepressants (i.e. clomipramine and citalopram) may improve psychosis in depressed patients. Finally, studies in the schizophrenia literature indicate that psychological approaches are effective in psychosis management but, to date, this strategy has been supported only qualitatively in PD, and further studies are warranted.

Pharmacogenetics of antiparkinsonian drug treatment: a systematic review

Pharmacotherapy is the mainstay in the treatment of Parkinson's disease and the armamentarium of drugs available for the therapy of this disease is still expanding. Anti-Parkinson's disease drugs are effective in reducing the physical symptoms, such as hypokinesia, bradykinesia, rigidity and tremor. However, there is a large interindividual variability in response to anti-Parkinson's disease drugs with respect to both drug efficacy and toxicity. It is thought that genetic variability in genes encoding drug-metabolizing enzymes, drug receptors and proteins involved in pathway signaling is an important factor in determining interindividual variability in drug response. Pharmacogenetics aims at identifying genetic markers associated with drug response. Ideally, knowledge of these genetic markers will enable us to predict an individual's drug response in terms of both efficacy and toxicity. The role of pharmacogenetics in the treatment of Parkinson's disease is relatively unexplored. Therefore, we aim to present a systematic review of the published pharmacogenetic studies in Parkinson's disease and to describe polymorphic genes of interest for future research.

Polymorphisms in dopamine receptor DRD1 and DRD2 genes and psychopathological and extrapyramidal symptoms in patients on long-term antipsychotic treatment

DRD(1) and DRD(2) receptor gene variants have been associated with clinical aspects of schizophrenia; however only specific features were analyzed in different samples. To assess the complex interaction between genetic and clinical factors, we studied the possible cross-interactions between DRD1 and DRD2 dopamine receptor gene polymorphisms, symptomatology of schizophrenia and schizoaffective disorders, and the occurrence of treatment induced side effects taking into consideration possible clinical confounding variables. One hundred thirty one outpatients in stable remission meeting the DSMIV criteria for schizophrenia spectrum disorders and receiving long-term maintenance therapy with haloperidol, fluphenazine, zuclopenthixole, or risperidone were genotyped for DRD1 A-48G, DRD2 Ins-141CDel, and DRD2 Ser311Cys polymorphisms. Psychopathological symptoms were assessed with the positive and negative syndrome scale for schizophrenia (PANSS). Extrapyramidal side effects were assessed with the Simpson-Angus extrapyramidal side effects scale (EPS), the Barnes Akathisia scale (BARS), and the abnormal involuntary movement scale (AIMS). Drug dosage was included as covariant because it was associated with the severity of symptomatology, akathisia, and parkinsonism. No association was observed for DRD1 and DRD2 polymorphisms and extrapyramidal side effects, or with the other clinical variables considered. Our study suggests that DRD1 and DRD2 variants are not liability factors for tardive dyskinesia.