The effect of monoamine oxidase B (MAOB) and catechol-O-methyltransferase (COMT) polymorphisms on levodopa therapy in patients with sporadic Parkinson's disease

Dopamine pathway and Parkinson's risk variants are associated with levodopa-induced dyskinesia

Background

Levodopa-induced dyskinesia (LID) is a common adverse effect of levodopa, one of the main therapeutics used to treat the motor symptoms of Parkinson's disease (PD). Previous evidence suggests a connection between LID and a disruption of the dopaminergic system as well as genes implicated in PD, including GBA1 and LRRK2.

Objectives

To investigate the effects of genetic variants on risk and time to LID.

Methods

We performed a genome-wide association study (GWAS) and analyses focused on GBA1 and LRRK2 variants. We also calculated polygenic risk scores including risk variants for PD and variants in genes involved in the dopaminergic transmission pathway. To test the influence of genetics on LID risk we used logistic regression, and to examine its impact on time to LID we performed Cox regression including 1,612 PD patients with and 3,175 without LID.

Results

We found that GBA1 variants were associated with LID risk (OR=1.65, 95% CI=1.21-2.26, p=0.0017) and LRRK2 variants with reduced time to LID onset (HR=1.42, 95% CI=1.09-1.84, p=0.0098). The fourth quartile of the PD PRS was associated with increased LID risk (ORfourth_quartile=1.27, 95% CI=1.03-1.56, p=0.0210). The third and fourth dopamine pathway PRS quartiles were associated with a reduced time to development of LID (HRthird_quartile=1.38, 95% CI=1.07-1.79, p=0.0128; HRfourth_quartile=1.38, 95% CI=1.06-1.78, p=0.0147).

Conclusions

This study suggests that variants implicated in PD and in the dopaminergic transmission pathway play a role in the risk/time to develop LID. Further studies will be necessary to examine how these findings can inform clinical care.

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.

Association of Catechol-O-Methyltransferase Gene Polymorphisms and Haplotypes in the Levodopa-Induced Adverse Events in Subjects with Parkinson's Disease

The presence of dyskinesia is the most common side effect of chronic administration of levodopa in Parkinson's disease (PD) subjects. Genetic polymorphisms in levodopa metabolizing gene, catechol-O-methyl transferase (COMT), is shown to influence the inter-individual variability in drug response and adverse events. In the present study, the association of COMT rs6269, rs4633, rs4818, and rs4680 polymorphisms and haplotypes on pharmacokinetics and adverse events with levodopa was investigated in 150 PD patients. The age of onset of PD was 58.00 ± 10 yrs. The most common side effect faced by 78% of the subjects was dyskinesia. The AUC of levodopa was found to be significantly higher in subjects with dyskinesia (1695 ± 113 ng/ml/hr, p < 0.0001) than those without dyskinesia (1550 ± 122 ng/ml/hr). We found that the frequency of subjects presenting dyskinesia was significantly higher in subjects carrying variant genotype of COMT rs6269, rs4633, and rs4680 than that with wild genotype and these subjects presented higher AUC of levodopa. In addition, in subjects with dyskinesia, the AUC of levodopa was found to be significantly higher with low COMT (ACCG) haplotype. The association of COMT rs6269, COMT rs4633, COMT rs4818, and COMT rs4680 variant genotypes with the risk of dyskinesia due to levodopa therapy showed an ROC AUC of 0.67 indicating the moderate prediction of dyskinesia (p = 0.0021) with these COMT variants. In conclusion, PD subjects carrying the variant genotypes of COMT strongly influence high levodopa-induced dyskinesia. Hence the genotyping of COMT before the levodopa therapy will be useful to reduce the adverse events associated with the chronic levodopa treatment.

Association of Catechol-O-Methyltransferase Gene rs4680 Polymorphism and Levodopa Induced Dyskinesia in Parkinson's Disease: A Meta-Analysis and Systematic Review

INTRODUCTION

Long-term levodopa therapy for Parkinson's disease (PD) can cause levodopa induced dyskinesia (LID). Genetic predisposition has a significant role to play in inter-individual heterogeneity in the clinical manifestation of LID. Despite accumulating evidence for the role of COMT gene polymorphism (rs4680) as a genetic basis for LID, to date results have been inconsistent. Early assessment of the Catechol-O-Methyltransferase (COMT) genotype might be helpful to stratify PD patients concerning their individual risk for LID.

METHOD

In this meta-analysis, we have used 9 studies, which were selected through online databases. Statistical analysis was performed using R (v-3.6) software. 5 genetic models have been used in the present study: Allele model (A vs. G), Dominant model (AA+AG vs. GG), Homozygote model (AA vs. GG), Co-dominant/heterozygote model (AG vs. GG), and Recessive model (AA vs. AG + GG).

RESULTS

The results indicated a significant association between COMT rs4680 (Val158Met) polymorphism and LID risk. The genotype AA of COMT rs4680 is a risk factor for LID in PD patients under the recessive model (AA vs GG+AG) in the random-effect model. Analysis based on ethnicity showed that COMT rs4680 SNP allele A is a risk factor for LID development in Asian PD patients, while GG genotype is a risk factor for LID development in non-Asian PD patients using different genetic models.

CONCLUSION

The results of the present meta-analysis support that the COMT Val158Met polymorphism is a risk factor for the development of LID in PD patients having ethnic variations.

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.

Functional MAOB Gene Intron 13 Polymorphism Predicts Dyskinesia in Parkinson’s Disease

Identification of individual risk factors for motor complications in Parkinson's disease (PD) can help to guide personalised medical treatment, particularly since treatment options are still limited. To determine whether common functional gene polymorphisms in the dopamine metabolism predict the onset of motor complications in PD, we performed a retrospective, observer-blinded follow-up study of 30 PD patients who underwent genotyping of dopa-decarboxylase (DDC; rs921451), monoamine oxidase B (MAOB; rs1799836), catechol-O-methyltransferase (COMT; rs4680), and dopamine transporter (DAT; variable number tandem repeat) polymorphisms. Onset of wearing-off and dyskinesias was determined by blinded clinical assessments. Predictive values of genotypes for motor complications were evaluated using Cox proportional hazard models. During a median follow-up time of 11.6 years, 23 (77%) of 30 PD patients developed wearing-off, 16 (53%) dyskinesias, and 23 (77%) any motor complication. The MAOB (rs1799836) polymorphism predicted development of dyskinesias with MAOB^CC/(C)/CT genotypes (resulting in low/intermediate brain enzyme activity) being associated with lower hazard ratios (unadjusted HR [95% CI]: 0.264 [0.089–0.787]; p=0.012; adjusted HR [95% CI]: 0.142 [0.039–0.520]; p=0.003) than MAOB^TT/(T) genotypes (resulting in high brain enzyme activity). DDC (rs921451), COMT (rs4680), and DAT (VNTR) polymorphisms were not predictive of motor complications. Together, the MAOB (rs1799836) polymorphism predicts the development of dyskinesias in PD patients. Our results need confirmation in larger cohorts. If confirmed, individual assessment of this polymorphism might be helpful for early risk stratification and could comprise a step towards patient-tailored therapeutic strategies to prevent or delay motor complications in the course of PD.

Association of COMT rs4680 and MAO-B rs1799836 polymorphisms with levodopa-induced dyskinesia in Parkinson's disease-a meta-analysis

BACKGROUND AND PURPOSE

Polymorphisms of the catechol-O-methyl transferase (COMT) or monoamine oxidase B (MAO-B) genes may affect the occurrence of dyskinesia in Parkinson's disease (PD) patients. However, the findings are inconsistent. Thus, we performed a meta-analysis to assess whether COMT and MAO-B genetic variants are associated with an increased incidence of levodopa-induced dyskinesia (LID) in PD patients.

METHODS

A literature search of PubMed, Embase, and Cochrane Library was conducted to identify relevant studies published up to January 2021. The strength of the association between the polymorphisms and LID susceptibility was estimated by odds ratio (OR) and associated 95% confidence interval (CI). The pooled ORs were assessed in different genetic models.

RESULTS

Ten studies involving 2385 PD patients were included in the meta-analysis. Analysis of pooled ORs and 95% CIs suggested that the AA genotype of COMT(rs4680) was associated with LID (OR = 1.39, 95%CI: 1.02-1.89, P = 0.039) in the recessive model, and this correlation was more obvious in Brazilian samples in the analysis stratified by ethnicity. For the AG genotype of MAO-B(rs1799836), the pooled OR was 1.66 (95% CI: 1.04-2.65, P = 0.03) in patients with LID versus those without LID in the heterozygote model.

CONCLUSIONS

Our meta-analysis implicates the AA genotype of the COMT rs4680 polymorphism as potentially increasing the risk of LID in a recessive genetic model for PD patients. Furthermore, the AG genotype of the MAO-B rs1799836 polymorphism may influence the prevalence of LID in PD patients in the heterozygote model. However, further well-designed studies with larger PD patient cohorts are required to validate these results after adjusting for confounding factors.

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.

Chronic Neurological Disorders: Genetic and Epigenetic Markers for Monitoring of Pharmacotherapy

Introduction

Chronic neurological diseases are a major cause of mortality and morbidity in the world. With increasing life expectancy in the developing world, the incidence and prevalence of these diseases are predicted to rise even further. This has also contributed to an increase in disability-adjusted life years (DALYs) for noncommunicable diseases. Treatment for such diseases also poses a challenge with multiple genetic and epigenetic factors leading to a varied outcome. Personalization of treatment is one way that treatment outcome/prognosis of disease can be improved, and pharmacogenomics plays a significant role in this context.

Methodology

This article reviewed the evidence pertaining to the association of genetic and epigenetic markers with major neurological disorders like multiple sclerosis (MS), Alzheimer's disease (AD), and Parkinson's disease (PD), which are a major source of burden among neurological disorders. Types of studies included are peer-reviewed original research articles from the PubMed database (1999-2018).

Results

This study compiled data regarding specific genetic and epigenetic markers with a significant correlation between the clinical diagnosis of the disease and prognosis of therapy from 65 studies. In a single platform, this review highlights the clues to some vital questions, such as why interferon beta (IFN-β) therapy fails to improve symptoms in all MS patients? why cholinesterase inhibitors fail to improve cognitive impairment in a subset of people suffering from AD? or why some individuals on levodopa (L-DOPA) for PD suffer from side-effects ranging from dyskinesia to hallucination while others do not?

Conclusion

This article summarizes the genetic and epigenetic factors that may either require monitoring or help in deciding future pharmacotherapy in a patient suffering from MS, AD, and PD. As the health care system develops and reaches newer heights, we expect more and more of these biomarkers to be used as pharmacotherapeutic outcome indicators.

Polymorphism of the Dopa-Decarboxylase Gene Modifies the Motor Response to Levodopa in Chinese Patients With Parkinson's Disease

Levodopa (L-DOPA) is the most effective drug for Parkinson's disease (PD). However, the response to L-DOPA remains individually variable, which hampers the practical value of L-DOPA in the clinic. Genetic factors play a role in L-DOPA efficacy. This study explored the associations between polymorphisms and motor response to L-DOPA in Chinese patients with PD. A total of 51 Chinese PD patients were enrolled in this study. Patients underwent an acute L-DOPA challenge and were evaluated by the Unified Parkinson Disease Rating Scale (UPDRS) part III at baseline and after L-DOPA administration. Subjects were genotyped for polymorphisms: rs921451 and rs3837091 in the DDC loci, rs3836790 in the SLC6A3 locus, rs4680 in the COMT locus, and rs1799836 in the MAOB locus. We found that patients carrying the DDC CT or TT genotype exhibited a better motor response to L-DOPA than patients with the DDC CC genotype, and there was still a significant difference after adjustment for the L-DOPA dose in the acute challenge. Improvement in the UPDRS III subscores, including bradykinesia and axial symptoms, was significantly lower in patients with the DDC CC genotype than in patients with the CT or TT genotype. There were no significant associations between the motor response to L-DOPA and the rs3837091, rs3836790, rs4680, and rs1799836 variants. The DDC single nucleotide polymorphism rs921451 modulated the motor response to L-DOPA in Chinese PD patients. Our results suggested that DDC may be a modifier gene for the L-DOPA treatment response in PD.

Extrastriatal SPECT-DAT uptake correlates with clinical and biological features of de novo Parkinson's disease

Striatal dopamine transporter (DAT) uptake assessment through I¹²³-Ioflupane Single-Pphoton Emission Computed Tomography (SPECT) provides valuable information about the dopaminergic denervation occurring in Parkinson's disease (PD). However, little is known about the clinical or biological relevance of extrastriatal DAT uptake in PD. Here, from the Parkinson's Progression Markers Initiative, we studied 623 participants (431 PD and 192 healthy controls) with available SPECT data. Even though striatal denervation was undoubtedly the imaging hallmark of PD, extrastriatal DAT uptake was also reduced in patients with PD. Topographically, widespread frontal but also temporal and posterior cortical regions showed lower DAT uptake in PD patients with respect to healthy controls. Importantly, a longitudinal voxelwise analysis confirmed an active one-year loss of extrastriatal DAT uptake within the PD group. Extrastriatal DAT uptake also correlated with the severity of motor symptoms, cognitive performance, and cerebrospinal fluid α-synuclein levels. In addition, we found an association between the Catechol-O-methyltransferase val¹⁵⁸met genotype and extrastriatal DAT uptake. These results highlight the clinical and biological relevance of extrastriatal SPECT-DAT uptake in PD.

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.

DAT gene polymorphisms (rs28363170, rs393795) and levodopa-induced dyskinesias in Parkinson's disease

L-dopa-induced dyskinesias (LID) is a common motor side effect of levodopa therapy of Parkinson's disease (PD). The identified predictors may only partially account for the risk of developing LID and genetic factors may contribute to this variability. The present study is aimed to investigate whether polymorphisms in the dopamine transporter gene (DAT) are associated with the risk of developing LID. Genotyping of the 40-bp VNTR (rs28363170) and rs393795 (A/C) polymorphisms of the DAT gene was performed in a well-characterized cohort of 181 Italian PD patients in treatment with L-DOPA for 3 years or more. The results of our study show that there is no difference in dyskinesias prevalence among carriers of the two DAT gene polymorphisms. However, the combination of the two genotypes 10R/10R (rs28363170) and A carrier (rs393795) of the DAT gene reduces the risk of LID occurrence during long-term therapy with l-DOPA with respect to the PD subjects who did not carry these alleles (OR = 0.31; 95% CI, 0.09-0.88). Also based on a logistic regression analysis, the 10R/10R and the A carrier allele of the rs393795 polymorphisms of the DAT gene, could reduce the susceptibility to develop LID during levodopa therapy adjusted by demographical and clinical variables (OR = 0.19; 95% CI, 0.05-0.69). Additional studies further investigating the rs28363170 and rs393795 polymorphisms with LID in PD are needed to clarify their role in different ethnicities.

MAO-B and COMT Genetic Variations Associated With Levodopa Treatment Response in Patients With Parkinson's Disease

The most commonly used Parkinson's disease (PD) treatment is the replacement of dopamine by its levodopa precursor (l-dopa). Monoamine oxidase-B (MAO-B) and catechol-o-methyl transferase (COMT) are enzymes involved in the metabolism and regulation of dopamine availability. In our study we investigated the possible relation among selected single-nucleotide polymorphisms (SNPs) in the MAO-B (rs1799836) and COMT (rs4680) genes and the therapeutic response to levodopa (l-dopa). A total of 162 Brazilian patients from the Pro-Parkinson service of Clinics Hospital of Pernambuco diagnosed with sporadic PD and treated with levodopa were enrolled. PD patients were stratified into 2 groups according to the daily levodopa dose. MAO-B and COMT SNP genotyping was conducted by polymerase chain reaction-restriction fragment length polymorphism. After multivariate analysis, we observed a significant difference between PD groups for the following variables: sex (P = .02), longer duration of disease (P = .02), longer levodopa therapy duration (P = .01), younger onset of PD (P = .01), and use of COMT inhibitor (P = .02). We observed that patients carrying MAO-B (rs1799836) A and AA genotypes and COMT (rs4680) LL genotype suffered more frequently from levodopa-induced-dyskinesia. In addition, we found an increased risk of 2.84-fold for male individuals carrying the MAO-B G allele to be treated with higher doses of levodopa (P = .04). We concluded that before beginning PD pharmacological treatment, it is important to consider the genetic variants of the MAO-B and COMT genes and the sex, reinforcing the evidence that sexual dimorphism in the genes related to dopamine metabolism might affect PD treatment.

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.

From Genomics to Omics Landscapes of Parkinson's Disease: Revealing the Molecular Mechanisms

Molecular mechanisms of Parkinson's disease (PD) have already been investigated in various different omics landscapes. We reviewed the literature about different omics approaches between November 2005 and November 2017 to depict the main pathological pathways for PD development. In total, 107 articles exploring different layers of omics data associated with PD were retrieved. The studies were grouped into 13 omics layers: genomics-DNA level, transcriptomics, epigenomics, proteomics, ncRNomics, interactomics, metabolomics, glycomics, lipidomics, phenomics, environmental omics, pharmacogenomics, and integromics. We discussed characteristics of studies from different landscapes, such as main findings, number of participants, sample type, methodology, and outcome. We also performed curation and preliminary synthesis of multiple omics data, and identified overlapping results, which could lead toward selection of biomarkers for further validation of PD risk loci. Biomarkers could support the development of targeted prognostic/diagnostic panels as a tool for early diagnosis and prediction of progression rate and prognosis. This review presents an example of a comprehensive approach to revealing the underlying processes and risk factors of a complex disease. It urges scientists to structure the already known data and integrate it into a meaningful context.

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.

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.

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.

Pharmacogenetic considerations in the treatment of Parkinson's disease

Recently, a lot of progress has been made in the identification of genetic biomarkers of drug response. Efforts to define the role of genetic polymorphisms in optimizing pharmacotherapy of Parkinson's disease were also undertaken. This report presents the current state of knowledge on pharmacogenetics of PD, including genes encoding enzymes involved in drug metabolism, drug transporters and direct targets of antiparkinsonian drugs. In most of cases, available data on pharmacogenetic factors that could turn out to be significant modifiers of therapy with anti-PD drugs is still very incomplete and makes it impossible to reach final conclusion about their usefulness in the clinic. More extensive studies, in more uniform, large patient groups, including genome-wide association studies, should be undertaken to finally confirm or deny the value of genetic tests in PD therapy individualization.

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.

Polymorphism of the dopamine transporter type 1 gene modifies the treatment response in Parkinson's disease

After more than 50 years of treating Parkinson's disease with l-DOPA, there are still no guidelines on setting the optimal dose for a given patient. The dopamine transporter type 1, now known as solute carrier family 6 (neurotransmitter transporter), member 3 (SLC6A3) is the most powerful determinant of dopamine neurotransmission and might therefore influence the treatment response. We recently demonstrated that methylphenidate (a dopamine transporter inhibitor) is effective in patients with Parkinson's disease with motor and gait disorders. The objective of the present study was to determine whether genetic variants of the dopamine transporter type 1-encoding gene (SLC6A3) are associated with differences in the response to treatment of motor symptoms and gait disorders with l-DOPA and methylphenidate (with respect to the demographic, the disease and the treatment parameters and the other genes involved in the dopaminergic neurotransmission). This analysis was part of a multicentre, parallel-group, double-blind, placebo-controlled, randomized clinical trial of methylphenidate in Parkinson's disease (Protocol ID:2008-005801-20; ClinicalTrials.gov:NCT00914095). We scored the motor Unified Parkinson's Disease Rating Scale and the Stand-Walk-Sit Test before and after a standardized acute l-DOPA challenge before randomization and then after 3 months of methylphenidate treatment. Patients were screened for variants of genes involved in dopamine metabolism: rs28363170 and rs3836790 polymorphisms in the SLC6A3 gene, rs921451 and rs3837091 in the DDC gene (encoding the aromatic L-amino acid decarboxylase involved in the synthesis of dopamine from l-DOPA), rs1799836 in the MAOB gene (coding for monoamine oxidase B) and rs4680 in the COMT gene (coding for catechol-O-methyltransferase). Investigators and patients were blinded to the genotyping data throughout the study. Eighty-one subjects were genotyped and 61 were analysed for their acute motor response to l-DOPA. The SLC6A3 variants were significantly associated with greater efficacy of l-DOPA for motor symptoms. The SLC6A3 variants were also associated with greater efficacy of methylphenidate for motor symptoms and gait disorders in the ON l-DOPA condition. The difference between motor Unified Parkinson's Disease Rating Scale scores for patients with different SLC6A3 genotypes was statistically significant in a multivariate analysis that took account of other disease-related, treatment-related and pharmacogenetic parameters. Our preliminary results suggest that variants of SLC6A3 are genetic modifiers of the treatment response to l-DOPA and methylphenidate in Parkinson's disease. Further studies are required to assess the possible value of these genotypes for (i) guiding l-DOPA dose adaptations over the long term; and (ii) establishing the risk/benefit balance associated with methylphenidate treatment for gait disorders.

Pharmacogenetics of drug response in Parkinson's disease

Parkinson's disease (PD) is a debilitating, demoralizing and financially devastating condition affecting 1% of population at the age of 60 years. Thus, very important issue to address is individual therapy optimization. Recent results have shown evidence that variable efficacy of treatment and risk of motor and mental complications could have genetic origin. Significant roles in that process play (pharmaco)genomic/genetic studies of PD. Variability in genes coding for drug-metabolizing enzymes, drug receptors and proteins involved in drug pathway signaling is an important factor determining inter-individual variability in drug responses. Interpersonal differences in drug responses are clearly documented although individualized treatment of PD is not widely known. Treatment with antiparkinsonian drugs is associated with the development of complications, such as L-DOPA-induced dyskinesia (LID), hallucinations and excessive daytime sleepiness. Carriers of specific genetic polymorphisms are particularly susceptible to development of some of these drug adverse effects. Pharmacogenomics aims to understand the relationship between genetic factors and inter-individual variations in drug responses, and to translate this information in therapy tailored to individual patient genetics. Relatively few efforts have been made to investigate the role of pharmacogenetics in the individual response to anti-PD drugs. Thus, many genetic variations and polymorphisms in myriad of different proteins can influence individual response to anti-PD drugs.

Association of Catechol-O-Methyltransferase and monoamine oxidase B gene polymorphisms with motor complications in parkinson's disease in a Chinese population

BACKGROUND

Catechol-O-Methyltransferase (COMT) and Monoamine oxidase B (MAO-B) are the main enzymes that metabolize dopamine in the brain. The polymorphisms of the COMT gene and MAO-B gene are associated with high, intermediate and low levels of activity. This may influence the prevalence of motor complications in Parkinson's Disease (PD).

METHODS

The study enrolled 1087 Chinese PD patients throughout the country. Sanger dideoxynucleotide chain termination methods were used for COMT and MAO-B genotyping. The researchers compared the association between presence of motor complications and COMT and MAO-B gene polymorphisms, both separately and in combination.

RESULTS

Comparison of the allele frequencies revealed that COMT (GG) was significantly more common among PD patients who exhibited wearing-off compared to PD patients without wearing-off (P < 0.05). A statistically higher frequency of the MAO-B (AG) genotype in PD patients with dyskinesias was found (P < 0.05). Although these differences were not significant after Bonferroni's correction. The combined haplotype of the MAO-B and COMT showed no increase (p < 0.05) in the risk of wearing-off and dyskinesias.

CONCLUSIONS

Our findings suggest that polymorphisms in COMT and MAO-B may increase the risk of wearing-off and dyskinesias. COMT (GG) genotype may be the risk factor of wearing-off. While MAO-B (AG) genotype may be the risk factor of dyskinesias.

Sequence variants in SLC6A3, DRD2, and BDNF genes and time to levodopa-induced dyskinesias in Parkinson's disease

Levodopa-induced dyskinesias (LID) present a common but elusive complication of levodopa therapy in Parkinson's disease (PD). In order to identify genetic factors associated with LID, 352 (213 males) levodopa-treated Israeli PD patients were genotyped for 34 polymorphisms within three candidate genes affecting dopaminergic activity and synaptic plasticity: dopamine transporter gene (DAT1 or SLC6A3) [14 single nucleotide polymorphisms (SNPs) and 40-bp variable number tandem repeat (VNTR)], DRD2 [11 SNPs and dinucleotide CA short tandem repeat (STR)], and BDNF (7 SNPs). A comparison of patients with and without LID was performed by applying a time-oriented approach, with survival analyses evaluating LID development hazard rate over time [Cox proportional hazards and accelerated failure time (AFT) lognormal models]. Overall, 192 (54.5 %) participants developed LID, with a mean latency of 5.0 (±4.5) years. After adjusting for gender, age at PD onset, duration of symptoms prior to levodopa exposure, and multiple testing correction, one SNP in SLC6A3 (with 81 % genotyping success) was significantly associated with LID latency: the C allele of the rs393795 extended the time to LID onset, time ratio = 4.96 (95 % CI, 2.3-10.9; p = 4.1 × 10(-5)). This finding should be validated in larger, ethnically diverse PD populations, and the biological mechanism should be explored.

Pharmacogenetics of Parkinson's disease - through mechanisms of drug actions

In the last years due to development of molecular methods a substantial progress in understanding of genetic associations with drug effects in many clinical disciplines has been observed. The efforts to define the role of genetic polymorphisms in optimizing pharmacotherapy of Parkinson’s disease (PD) were also undertaken. So far, some promising genetic loci for PD treatment were determined. In the review pharmacogenetic aspects of levodopa, dopamine agonists and COMT inhibitors are discussed.

EDdb: a web resource for eating disorder and its application to identify an extended adipocytokine signaling pathway related to eating disorder

Eating disorder is a group of physiological and psychological disorders affecting approximately 1% of the female population worldwide. Although the genetic epidemiology of eating disorder is becoming increasingly clear with accumulated studies, the underlying molecular mechanisms are still unclear. Recently, integration of various high-throughput data expanded the range of candidate genes and started to generate hypotheses for understanding potential pathogenesis in complex diseases. This article presents EDdb (Eating Disorder database), the first evidence-based gene resource for eating disorder. Fifty-nine experimentally validated genes from the literature in relation to eating disorder were collected as the core dataset. Another four datasets with 2824 candidate genes across 601 genome regions were expanded based on the core dataset using different criteria (e.g., protein-protein interactions, shared cytobands, and related complex diseases). Based on human protein-protein interaction data, we reconstructed a potential molecular sub-network related to eating disorder. Furthermore, with an integrative pathway enrichment analysis of genes in EDdb, we identified an extended adipocytokine signaling pathway in eating disorder. Three genes in EDdb (ADIPO (adiponectin), TNF (tumor necrosis factor) and NR3C1 (nuclear receptor subfamily 3, group C, member 1)) link the KEGG (Kyoto Encyclopedia of Genes and Genomes) "adipocytokine signaling pathway" with the BioCarta "visceral fat deposits and the metabolic syndrome" pathway to form a joint pathway. In total, the joint pathway contains 43 genes, among which 39 genes are related to eating disorder. As the first comprehensive gene resource for eating disorder, EDdb ( http://eddb.cbi.pku.edu.cn ) enables the exploration of gene-disease relationships and cross-talk mechanisms between related disorders. Through pathway statistical studies, we revealed that abnormal body weight caused by eating disorder and obesity may both be related to dysregulation of the novel joint pathway of adipocytokine signaling. In addition, this joint pathway may be the common pathway for body weight regulation in complex human diseases related to unhealthy lifestyle.

Association Between Catechol-O-Methyltransferase (COMT) Gene Polymorphisms, Parkinson's Disease, and Levodopa Efficacy

OBJECTIVES

We investigated the association between catechol-O-methyltransferase (COMT) gene polymorphisms and Parkinson's disease (PD) susceptibility, severity of disease, and levodopa (L-Dopa) efficacy.

SUBJECTS AND METHODS

Patients (N = 97) with primary PD and healthy volunteers (N = 102) were recruited. Disease severity was assessed with the Unified Parkinson's Disease Rating Scale (UPDRS) and Hoehn & Yahr grade at 'On stage'. Genomic DNA was extracted from blood cells. Polymerase chain reaction and sequencing were used to detect COMT mutations. Data were analyzed by SPSS 18.0. False discovery rate (FDR) or Bonferroni correction was used if the result showed P < 0.05.

RESULTS

Four COMT mutations were detected in 199 subjects: rs74745580 (only in two patients with primary PD), rs4633, rs6267, and rs3838146. There were no statistical differences in frequencies of rs4633, rs6267, and rs3838146 genotypes between PD patients and the control group. The frequency of allele rs4633T was higher in PD patients than in the control group. UPDRS score was lower in rs4633 (CT/TT) carriers and rs3838146 (-C/- -) carriers than in rs4633 (CC) and rs3838146 (CC) carriers. PD patients carrying rs6267 (GT/TT) had higher UPDRS scores than patients with rs6267 (GG) (P < 0.05). The frequencies of the three polymorphisms were not statistically different between patients who did and did not receive L-Dopa; dose and duration of L-Dopa treatment did not differ between genotypes; and there was also no difference in the ratios of loss of efficacy towards levodopa.

CONCLUSIONS

The polymorphisms rs4633, rs6267, and rs3838146 were associated with severity of PD but were not associated with L-Dopa medication.

Dopa-decarboxylase gene polymorphisms affect the motor response to L-dopa in Parkinson's disease

BACKGROUND

In Parkinson's disease (PD), the response to L-dopa is highly variable and unpredictable. The major pathway for dopamine synthesis from L-dopa is decarboxylation by aromatic L-amino acid decarboxylase (AAAD, encoded by the DDC gene).

OBJECTIVE

To determine the motor response to L-dopa in PD patients as a function of the DDC gene promoter polymorphisms (rs921451 T > C polymorphism (DDC(T/C)) and rs3837091 AGAG del (DDC(AGAG/-))).

METHODS

Thirty-three Caucasian PD patients underwent an acute l-dopa challenge together with the peripheral AAAD inhibitor benserazide and were genotyped for rs921451 and rs3837091. The primary efficacy criterion was the motor response to L-dopa, as estimated by the area under the curve for the change in the Unified Parkinson's Disease Rating Scale part III (UPDRS) score relative to baseline (AUCΔUPDRS) in the 4 h following L-dopa administration. Secondary endpoints were pharmacokinetic parameters for plasma levels of L-dopa and dopamine. Investigators and patients were blinded to genotypes data throughout the study.

RESULTS

When adjusted for the L-dopa dose, the AUCΔUPDRS was significantly lower in DDC(CC/CT) patients (n = 14) than in DDC(TT) patients (n = 19) and significantly lower in DDC(-/- or AGAG/-) patients (n = 8) than in DDC(AGAG/AGAG) patients (n = 25). There were no significant intergroup differences in plasma pharmacokinetic parameters for L-dopa and dopamine.

DISCUSSION

The rs921451 and rs3837091 polymorphisms of the DDC gene promoter influence the motor response to L-dopa but do not significantly change peripheral pharmacokinetic parameters for L-dopa and dopamine. Our results suggest that DDC may be a genetic modifier of the l-dopa response in Parkinson's disease.

Anti-Parkinson's disease drugs and pharmacogenetic considerations

INTRODUCTION

The development of pharmacogenetic-based clinical practice guidelines for the use of anti-Parkinson's disease drugs requires, as a pre-requisite, the identification and validation of genetic biomarkers. These biomarkers are then used as surrogate endpoints. This review analyzes potential genetic biomarkers which can be used to improve anti-Parkinson's disease therapy.

AREAS COVERED

The authors present an overview of current knowledge of pharmacogenetic implications of anti-Parkinson's disease drugs, including genes coding for the corresponding drug-metabolizing enzymes and drug targets. The gene/drug pairings with the strongest potential for pharmacogenetic recommendations include: CYP2C19/benztropine, COMT/levodopa and entacapone, CYP2B6/selegiline, UGT1A/entacapone, DRD2/ropinirole, pramipexole and cabergoline, and DRD3/ropinirole and pramipexole. Evidence supporting the effect of substrates, inhibitor or inducers for drug specific metabolizing enzymes in anti-Parkinson's disease drug response includes CYP1A2 in the response to ropinirole and rasagiline, and CYP3A4 in the response to bromocriptine, lisuride, pergolide and cabergoline. The authors present and discuss the current information on gene variations according to the 1000 genomes catalog and other databases with regards to anti-Parkinson's disease drugs. They also review and discuss the clinical implications of these variations.

EXPERT OPINION

The goal of pharmacogenomic testing for anti-Parkinson's disease drugs should be conservative and aimed at selecting determined drugs for determined patients. However, much additional research is still needed to obtain reliable pre-prescription tests.

Enhancing dopamine treatments: worth the effort?

SUMMARY Dopamine-based treatments underlie our current management of the motor symptoms of Parkinson’s disease. In this article, we look at the development of levodopa therapy, combination therapies with levodopa/dopa decarboxylase inhibitors, use of dopamine agonists, monoamine oxidase inhibitors, catechol-O-methyl transferase inhibitors and the development of nonoral delivery methods, in particular in the treatment of motor complications in later PD. There are some shortcomings of dopamine-based therapies including a limited benefit on the non-motor manifestations of Parkinson’s disease. We conclude by looking at the themes for future developments to further enhance dopamine delivery methods.

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.

Pharmacological treatment and the prospect of pharmacogenetics in Parkinson's disease

Parkinson disease (PD) is a progressive movement disorder marked by tremor, rigidity, bradykinesia and postural instability. Levodopa (l-dopa), usually combined with a peripheral dopa decarboxylase inhibitor, has been proved to provide the best symptomatic benefit for PD. However, its long-term efficacy is limited because of motor complications and drug-induced dyskinesia. Dopamine agonists, catechol-O-methyltransferase inhibitors and monoamine oxidase-B inhibitors are anti-parkinsonian (anti-PD) drugs that have been found to further improve the potency of l-dopa and prevent the onset of motor complications. However, as PD is a progressive disorder, all the drugs used for its therapy, manifest reduced efficacy and adverse effects with time. Research on the field of pharmacogenetics has pointed out that the genetic variability of each individual determines to a large extent the inter-individual variability in response to anti-PD drugs. Clinicogenetic trials show that drug efficacy or toxicity or susceptibility to side effects are features governed by genetic principles. This article is a review of the present pharmacological treatment of PD and current pharmacogenetic data for PD.

Association of the DRD2 and DRD3 polymorphisms with response to pramipexole in Parkinson's disease patients

OBJECTIVE

To evaluate the impact of the DRD2 TaqIA and DRD3 Ser9Gly polymorphisms on the efficacy of pramipexole in treating patients with Parkinson's disease (PD).

METHODS

Thirty patients with PD prospectively received pramipexole 0.25 mg three times daily for 2 months. Unified Parkinson Disease Rating Scale (UPDRS) assessments were conducted at baseline and 2 months after treatment initiation. Improvement by 20% or more in the total score on the UPDRS was considered to indicate responsiveness. The PCR-restriction fragment length polymorphism analysis was used to analyze the DRD2 Taq1A and DRD3 Ser9Gly genotype.

RESULTS

The DRD2 Taq1A allele frequencies were A141.7 (A1) and 58.3% (A2), and the DRD3 Ser9Gly allele frequencies were 68.3 (Ser) and 31.7% (Gly). When the subjects were grouped by the DRD3 Ser9Gly polymorphism, the response rates for pramipexole treatment were significantly higher in the Ser/Ser group (60%) than in the group containing the Gly allele (13%). There was a significant association between the DRD3 Ser9Gly polymorphism and response rate to pramipexole in PD patients (P = 0.024). When the subjects were grouped by the DRD2 Taq1A polymorphism, there were no significant differences among the three Taq1A genotypes.

CONCLUSIONS

DRD3 Ser9Gly polymorphisms are significantly associated with the therapeutic efficacy of pramipexole in Chinese patients with PD. A large-scale and multi-dose group study in patients with PD is necessary for evaluating the impact of the genetic polymorphisms of the dopamine receptor on the therapeutic effects of pramipexole.

The association of functional catechol-O-methyltransferase haplotypes with risk of Parkinson's disease, levodopa treatment response, and complications

INTRODUCTION

Differences in catechol-O-methyltransferase (COMT) activity and genotype may determine individual variations in the therapeutic response to levodopa or Parkinson's disease (PD) susceptibility. The role of functional COMT haplotypes in PD susceptibility and treatment response has not been examined.

OBJECTIVES

In this case-control study, we investigated the association of the most common COMT gene haplotypes (formed by single nucleotide polymorphisms (SNPs): rs6269:A>G; rs4633C>T; rs4818:C>G; and rs4680:A>G) with PD risk and the association of the COMT haplotypes with the dose and complications of levodopa therapy in PD patients.

METHODS

A total of 679 study participants (322 PD and 357 controls) were included. Each participant was genotyped for four SNPs in the COMT gene, located in a common haploblock, that has been shown to influence COMT enzymatic activity. The influence of COMT haplotypes on the dose of levodopa administered during fifth year of treatment, and occurrence of motor complications were examined in PD patients. The EH program (Jurg Ott, Rockefeller University, New York, USA) was used to estimate haplotype frequencies.

RESULTS

The estimated frequencies of low (A_C_C_G) and medium (A_T_C_A) activity haplotypes tended to be slightly lower among PD patients when compared with controls (P=0.09, G_C_G_G-high activity haplotype as reference). The frequency of G_C_G_G (high activity) haplotype carriers was higher in late onset PD patients (P=0.04) compared with controls. The mean levodopa dose increased with the activity of the functional haplotypes (low<medium<high). Doses prescribed for G_C_G_G (high activity) haplotype carriers (mean 604.2+/-261.9 mg) were significantly higher than those for the noncarriers (mean 512.2+/-133.5 mg, P<0.05). The COMT haplotype seemed to have little influence on the development of levodopa-induced dyskinesias.

CONCLUSION

Our study showed a possible association of functional COMT haplotypes with the risk of PD. Both nonsynonymous and synonymous SNPs within functional COMT haplotype blocks may be more relevant than individual SNPs in conferring PD susceptibility. The doses of levodopa treatment can be influenced by specific COMT haplotypes and this may be useful in instituting individualized therapy for PD patients.

Catechol-O-methyltransferase (COMT) gene variants: possible association of the Val158Met variant with opiate addiction in Hispanic women

Catechol-O-methyltransferase (COMT) catalyzes the breakdown of catechol neurotransmitters, including dopamine, which plays a prominent role in drug reward. A common single nucleotide polymorphism (SNP), G472A, codes for a Val158Met substitution and results in a fourfold down regulation of enzyme activity. We sequenced exon IV of COMT gene in search for novel polymorphisms and then genotyped four out of five identified by direct sequencing, using TaqMan assay on 266 opioid-dependent and 173 control subjects. Genotype frequencies of the G472A SNP varied significantly (P = 0.029) among the three main ethnic/cultural groups (Caucasians, Hispanics, and African Americans). Using a genotype test, we found a trend to point-wise association (P = 0.053) of the G472A SNP in Hispanic subjects with opiate addiction. Further analysis of G472A genotypes in Hispanic subjects with data stratified by gender identified a point-wise significant (P = 0.049) association of G/A and A/A genotypes with opiate addiction in women, but not men. These point-wise significant results are not significant experiment-wise (at P < 0.05) after correction for multiple testing. No significant association was found with haplotypes of the three most common SNPs. Linkage disequilibrium patterns were similar for the three ethnic/cultural groups.

Defining drug disposition determinants: a pharmacogenetic-pharmacokinetic strategy

In preclinical and early clinical drug development, information about the factors influencing drug disposition is used to predict drug interaction potential, estimate and understand population pharmacokinetic variability, and select doses for clinical trials. However, both in vitro drug metabolism studies and pharmacogenetic association studies on human pharmacokinetic parameters have focused on a limited subset of the proteins involved in drug disposition. Furthermore, there has been a one-way information flow, solely using results of in vitro studies to select candidate genes for pharmacogenetic studies. Here, we propose a two-way pharmacogenetic-pharmacokinetic strategy that exploits the dramatic recent expansion in knowledge of functional genetic variation in proteins that influence drug disposition, and discuss how it could improve drug development.

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.

A monoamine oxidase B gene variant and short-term antidepressant treatment response

Genetic differences among patients suffering from Major Depression are likely to contribute to interindividual differences in medication treatment response. Thus, the identification of gene variants affecting drug response is needed in order to be able to predict response to psychopharmacological drugs. This study analyzed a possible association of the common A644G single nucleotide polymorphism (SNP) within intron 13 of the monoamine oxidase B (MAOB) gene with antidepressant treatment response. The study population consisted of n = 102 patients with major depression (criteria of the Diagnostic and Statistical Manual of Mental Disorders, 4th Edition; DSM-IV) participating in a randomized double-blind controlled clinical trial, conducted at 50 centers in Germany, comparing the efficacy of mirtazapine and paroxetine during 6 weeks of treatment. Overall, female patients homozygous for the A-allele had a significantly faster and more pronounced antidepressant treatment response than AG/GG-carriers. In paroxetine-treated females these differences remained statistically significant. In mirtazapine-treated females homozygous for the A-allele compared to AG/GG-carriers, HAMD-17 scores during the study period were constantly and markedly lower, but not statistically different. In males, we found no association between the MAOB A644G intron 13 SNP and antidepressant treatment response. Our data provide first suggestive evidence that the MAOB A644G SNP is involved in the outcome of treatment with mirtazapine or paroxetine in females with major depression. To confirm the role of the MAOB A644G gene variant in antidepressant treatment response, independent replications are needed. If replicated, the MAOB A644G polymorphism could be considered useful for prospective confirmatory pharmacogenetic trials in patients with major depression.

Effect of MTHFR Polymorphisms on Hyperhomocysteinemia in Levodopa-treated Parkinsonian Patients

High plasma homocysteine levels have been observed in Parkinson's disease (PD) patients treated with levodopa. In this study, we investigated the effects of C677T and A1298C MTHFR polymorphisms, in association with L-DOPA daily dose and vitamin status, on hyperhomocysteinemia development in PD patients. Plasma homocysteine and folate/vitamin B12 levels were assayed in 49 L-DOPA-treated PD patients, and compared with those of 86 healthy subjects. Genotyping for MTHFR polymorphisms was carried out by DG-DGGE. Homocysteine levels were significantly higher in patients than in controls (16.3 +/- 5.7 vs. 11.7 +/- 2.7 micromol/l, P < 0.01). No significant differences were found between patients and controls with regard to folate/vitamin B12 levels, and MTHFR allele distribution. The TT+AA genotype was significantly more frequent in PD patients than in controls (32.5% vs. 17.4%, P < 0.05), but not associated with an increased risk for PD (OR = 2.3, CI = 1.0-5.2). Further, patients carrier of this genotype exhibited a mild hyperhomocysteinemia (22.1 +/- 4.9 micromol/l), while a protective effect was observed in patients having the CC+AA genotype (11.2 +/- 1.6 micromol/l; OR = 0.19, CI = 0.06-0.59). Interestingly, homocysteine levels were also moderately increased in patients with CT heterozygous genotype, in the context of either AA or AC (14.5 +/- 3.6 micromol/l), in comparison to subjects with the CC + AA genotype. Finally, we did not find any significant association of combined C677T and A1298C MTHFR polymorphisms with an increased risk for hyperhomocysteinemia in PD patients. A better understanding of the role of homocysteine and MTHFR genotypes in PD is needed to reveal novel approaches for disease management.