The DRD2 TaqIA polymorphism and demand of dopaminergic medication in Parkinson's disease

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.

Identification of Hub Genes and Potential Molecular Pathogenesis in Substantia Nigra in Parkinson's Disease via Bioinformatics Analysis

Parkinson's disease (PD) is the second most common neurodegenerative disease, with significant socioeconomic burdens. One of the crucial pathological features of PD is the loss of dopaminergic neurons in the substantia nigra (SN). However, the exact pathogenesis remains unknown. Moreover, therapies to prevent neurodegenerative progress are still being explored. We performed bioinformatics analysis to identify candidate genes and molecular pathogenesis in the SN of patients with PD. We analyzed the expression profiles, GSE49036 and GSE7621, which included 31 SN tissues in PD samples and 17 SN tissues in healthy control samples, and identified 86 common differentially expressed genes (DEGs). Then, GO and KEGG pathway analyses of the identified DEGs were performed to understand the biological processes and significant pathways of PD. Subsequently, a protein-protein interaction network was established, with 15 hub genes and four key modules which were screened in this network. The expression profiles, GSE8397 and GSE42966, were used to verify these hub genes. We demonstrated a decrease in the expression levels of 14 hub genes in the SN tissues of PD samples. Our results indicated that, among the 14 hub genes, DRD2, SLC18A2, and SLC6A3 may participate in the pathogenesis of PD by influencing the function of the dopaminergic synapse. CACNA1E, KCNJ6, and KCNB1 may affect the function of the dopaminergic synapse by regulating ion transmembrane transport. Moreover, we identified eight microRNAs (miRNAs) that can regulate the hub genes and 339 transcription factors (TFs) targeting these hub genes and miRNAs. Subsequently, we established an mTF-miRNA-gene-gTF regulatory network. Together, the identification of DEGs, hub genes, miRNAs, and TFs could provide better insights into the pathogenesis of PD and contribute to the diagnosis and therapies.

Clustering of Parkinson subtypes reveals strong influence of DRD2 polymorphism and gender

Most classification approaches for idiopathic Parkinson’s disease subtypes primarily focus on motor and non-motor symptoms. Besides these characteristics, other features, including gender or genetic polymorphism of dopamine receptors are potential factors influencing the disease’s phenotype. By utilizing a kmeans-clustering algorithm we were able to identify three subgroups mainly characterized by gender, DRD2 Taq1A (rs1800497) polymorphism—associated with changes in dopamine signaling in the brain—and disease progression. A subsequent regression analysis of these subgroups further suggests an influence of their characteristics on the daily levodopa dosage, an indicator for medication response. These findings could promote further enhancements in individualized therapies for idiopathic Parkinson’s disease.

Nardosinone Alleviates Parkinson's Disease Symptoms in Mice by Regulating Dopamine D2 Receptor

Nardostachyos Radix et Rhizoma (nardostachys) is the root and rhizome of Nardostachys jatamansi DC. Recent studies have shown that nardostachys may exert an anti-PD effect. In this study, the UHPLC-LTQ-Orbitrap-MS method was used to analyze the brain components of nardostachys in rats. Based on the results of UHPLC-LTQ-Orbitrap-MS analysis, nardosinone was identified to be the most effective anti-PD compound in nardostachys. To further verify this inference, a mouse PD model was established and the effect of nardosinone on PD mice was determined using classic behavioral tests. The results showed that nardosinone was indeed effective for relieving PD symptoms in mice. Moreover, network pharmacology analysis was used to elucidate the mechanism underlying the anti-PD effect of nardosinone. Dopamine receptor D2 (DRD2) was identified as the key target of nardosinone-PD interaction network, which was further verified by molecular docking and Western blotting. The results demonstrated that nardosinone and DRD2 could interact with each other. Furthermore, the expression level of DRD2 was decreased in the brain tissue of PD mice, and nardosinone could restore its expression to a certain extent. In conclusion, our findings suggest that nardosinone may reduce the motor and cognitive symptoms in the animal PD model by regulating DRD2 expression.

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.

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.

Association between the DRD2 TaqIA gene polymorphism and Parkinson disease risk: an updated meta-analysis

BACKGROUND

DRD2 TaqIA polymorphism may be associated with an increased risk of developing Parkinson disease (PD). However, the individual study's results are still inconsistent.

METHODS

A meta-analysis of 4232 cases and 4774 controls from 14 separate studies were performed to explore the possible relationship between the DRD2 TaqIA gene polymorphism and PD. Pooled odds ratios (ORs) for the association and the corresponding 95% confidence intervals (CIs) were evaluated by a fixed-effect model.

RESULTS

The pooled results revealed a significant association between DRD2 gene TaqIA polymorphism under recessive genetic model (OR: 0.91, 95% CI:0.83,0.99, P = .031) and additive genetic models (OR:0.93,95%CI:0.87,0.99, P = .032), but not associated with PD susceptibility under other genetic models in the whole population. Moreover, subgroups based on ethnicity and genotyping methods showed this association in the Caucasian subgroup under recessive genetic model (OR: 0.85, 95% CI:0.76,0.95, P = .003) and additive genetic models (OR:0.87,95%CI:0.79,0.96, P = .004) were existed. Besides, no significant association was detected under 6 genetic models in the Asian populations and PCR-RFLP subgroup.

CONCLUSIONS

The current meta-analysis suggested that a significant association between DRD2 TaqIA polymorphism and PD under the recessive genetic mode, and additive genetic models, especially in Caucasians.

Axonal degeneration in Parkinson's disease - Basal ganglia circuitry and D2 receptor availability

Basal ganglia (BG) circuitry plays a crucial role in the control of movement. Degeneration of its pathways and imbalance of dopaminergic signalling goes along with movement disorders such as Parkinson's disease. In this study, we explore the interaction of degeneration in two BG pathways (the nigro-striatal and dentato-pallidal pathway) with D2 receptor signalling to elucidate an association to motor impairment and medication response. Included in the study were 24 parkinsonian patients [male, 62 years (± 9.3 SD)] compared to 24 healthy controls [male, 63 years (± 10.2 SD)]; each participant passed through three phases of the study (i) acquisition of metadata/clinical testing, (ii) genotyping and (iii) anatomical/diffusion MRI. We report a decline in nigro-striatal (p < .003) and dentato-pallidal (p < .0001) connectivity in the patients compared to controls, which is associated with increasing motor impairment (relating to nigro-striatal, r = -0.48; p < .001 and dentato-pallidal connectivity, r = -0.36; p = .035). Given, that variations of the ANKK1 Taq1 (rs 1,800,497) allele alters dopamine D2-dependent responses, all participants were genotyped respectively. By grouping patients (and controls) according to their ANKK1 genotype, we demonstrate a link between D2 receptor signalling and decline in connectivity in both investigated pathways for the A1- variant (nigro-striatal pathway: r = -0.53; p = .012, dentato-pallidal pathway: r = -0.62; p = .0012). In patients with the A1+ variant, we only found increased brain connectivity in the dentato-pallidal pathway (r = 0.71; p = .001) correlating with increasing motor impairment, suggesting a potentially compensatory function of the cerebellum. Related to medication response carriers of the A1+ variant had a better drug effect associated with stronger brain connectivity in the nigro-striatal pathway (r = 0.54; p < .02); the A1- group had a good medication response although nigro-striatal connectivity was diminished (r = -0.38; p < .05); these results underscore differences in receptor availability between both groups in the nigro-striatal pathway. No effect onto medication response was found in the dentato-pallidal pathway (p > .05). Interplay between basal ganglia connectivity and D2 receptor availability influence the clinical presentation and medication response of parkinsonian patients. Furthermore, while current models of basal-ganglia function emphasize that balanced activity in the direct and indirect pathways is required for normal movement, our data highlight a role of the cerebellum in compensating for physiological imbalances in this respect.

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.

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.

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.

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.

Polymorphisms in the dopamine transporter gene are associated with visual hallucinations and levodopa equivalent dose in Brazilians with Parkinson's disease

The requirement for dopaminergic drugs in Parkinson's disease (PD) is highly variable. Visual hallucinations are a frequent and serious complication of chronic levodopa therapy. Polymorphisms in the DAT1 gene might affect the reuptake of dopamine in the synaptic cleft, but the influence of this variability on adverse effects or levodopa equivalent dose on PD patients is still poorly investigated. Therefore, the aim of the present study was to investigate DAT1 gene polymorphisms on levodopa equivalent dose and visual hallucination occurrence in PD patients. Altogether, 196 PD patients in treatment with at least 200 mg levodopa equivalent dose for at least 1 yr were included. These patients were genotyped for the -839 C > T and 3' VNTR DAT1 polymorphisms by PCR-based methodologies. Visual hallucinations occurred in 25.5% of the sample. After controlling for confounders, the dopamine transporter (DAT) -839 C allele was associated with visual hallucinations (prevalence ratio 2.5, 95% confidence intervals 1.13-5.5, p = 0.02). Levodopa equivalent dose was lower in carriers of the nine repeat allele of the DAT 3'UTR VNTR (741.2 ± 355.0 vs. 843.4 ± 445.7), explaining 21% of dose variability (p = 0.01). Our results support an effect of DAT1 polymorphisms in adverse effects of anti-Parkinsonian drugs and in levodopa equivalent dose usage.

Krüppel-like factor 11 differentially couples to histone acetyltransferase and histone methyltransferase chromatin remodeling pathways to transcriptionally regulate dopamine D2 receptor in neuronal cells

The importance of Krüppel-like factor (KLF)-mediated transcriptional pathways in the biochemistry of neuronal differentiation has been recognized relatively recently. Elegant studies have revealed that KLF proteins are important regulators of two major molecular and cellular processes critical for neuronal cell differentiation: neurite formation and the expression of neurotransmitter-related genes. However, whether KLF proteins mediate these key processes in a separate or coordinated fashion remains unknown. Moreover, knowledge on the contribution of chromatin dynamics to the biochemical mechanisms utilized by these proteins to perform their function is absent. Here we report the characterization of two antagonistic, chromatin-mediated mechanisms by which KLF11, also known as TIEG2 (transforming growth factor-β-inducible early gene 2) and MODY VII (maturity onset diabetes of the young VII), regulates transcription of the fopamine D2 receptor (Drd2) gene. First, KLF11 activates transcription by binding to a distinct Sp-KLF site within the Drd2 promoter (-98 to -94) and recruiting the p300 histone acetyltransferase. Second, Drd2 transcriptional activation is partially antagonized by heterochromatin protein 1 (HP1), the code reader for histone H3 lysine 9 methylation. Interestingly, KLF11 regulates neurotransmitter receptor gene expression in differentiating neuronal cell populations without affecting neurite formation. Overall, these studies highlight histone methylation and acetylation as key biochemical mechanisms modulating KLF-mediated neurotransmitter gene transcription. These data extend our knowledge of chromatin-mediated biochemical events that maintain key phenotypic features of differentiated neuronal cells.

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.

Large differences in levodopa dose requirement in Parkinson's disease: men use higher doses than women

BACKGROUND AND PURPOSE

The characteristics of levodopa dosing are not well described in the literature. The aims were to investigate the use of levodopa in a nationwide Swedish survey and to study the characteristics of low-dose and high-dose patients with Parkinson's disease (PD) in a university hospital.

METHODS

Patients with >or= 1 and >or= 2 purchases of levodopa during 2007 were selected from the prescribed drug register. Daily levodopa doses were estimated. Records of 504 patients with PD who visited the neurology clinic at Uppsala University Hospital during 2006-2007 were examined to select a low-dose group (< or = 400 mg levodopa daily, n = 21) and a high-dose group (>or= 1200 mg daily, n = 26) with at least 5 years of PD duration.

RESULTS

In total, 33 534 levodopa users with > or = 1 levodopa purchase were found. Daily levodopa dose range was large; median daily dose was 465 mg for men and 395 mg for women (P < 0.0001). Almost half (46%) of the patients used < 400 mg levodopa daily. Significantly, more men were treated with doses >or= 1200 mg daily. Dose and age correlated negatively (P < 0.0001). Patients with high dose at 5 years PD duration continuously increased their dosage the following years, whereas low-dose patients did not. The occurrence of dyskinesias was about the same in both groups despite the large difference in levodopa dose.

CONCLUSIONS

We conclude that the levodopa requirement in PD ranges considerably, and that men use higher levodopa dose than women. Levodopa requirement is constant during the progression of the disease in low-dose patients but increases in high-dose patients.