Association of common genetic variants of HOMER1 gene with levodopa adverse effects in Parkinson's disease patients

Critical evaluation of the current landscape of pharmacogenomics in Parkinson's disease - What is missing? A systematic review

INTRODUCTION

The first-line treatment for Parkinson's disease (PD) involves dopamine-replacement therapies; however, significant variability exists in patient responses. Pharmacogenomics has been explored as a potential approach to understanding and predicting treatment outcomes. This review aims to evaluate the current state of knowledge regarding the role of pharmacogenomics in PD, focusing on identifying challenges and proposing future directions.

METHODS

We conducted a systematic review following PRISMA 2020 guidelines. The PubMed database was searched for original, English-language studies using the R package 'RISmed.' Data were extracted and analyzed based on sample size, population origin, evaluated genes and polymorphisms, outcomes, and methodological approaches.

RESULTS

Out of 183 identified articles, 76 met the inclusion criteria. The COMT-rs4680 polymorphism was the most frequently studied, and levodopa-related motor complications were the most commonly assessed outcomes. All but two studies employed a candidate gene approach. In 75 % of the studies, the sample size was fewer than 225 individuals. There was a notable underrepresentation of Latino participants, with a lack of studies from Latin American countries other than Brazil. None of the studies produced consistent results across investigations.

CONCLUSIONS

The variability in patient responses to PD treatments suggests a genetic predisposition. While current research has enhanced our understanding of PD medication metabolism, it has not yet fully elucidated the complex genetic interactions involved in PD pharmacogenomics. Novel approaches, larger and more genetically diverse cohorts, and improved data collection are essential for advancing pharmacogenomics in PD clinical practice.

HOMER1 Polymorphism and Parkinson's Disease-Psychosis: Is there an Association?

Objective

Homer1, a postsynaptic protein coded by the HOMER1 gene, presumably has a role in homeostatic plasticity that dampens neuronal responsiveness when the input activity is too high. HOMER1 polymorphism has been studied in major psychiatric disorders such as schizophrenia. The objective of this study is to investigate if polymorphisms of the HOMER1 gene are associated with psychosis in Parkinson's disease (PD-P).

Methods

One hundred patients with Parkinson's disease (PD) and 100 healthy controls were enrolled consecutively in a PD-P biomarker study at the National Institute of Mental Health and Neurosciences, Bangalore, India. Of the 100 PD patients, 50 had psychosis (PD-P) and 50 did not have psychosis (PD-NP). Two single-nucleotide polymorphisms of HOMER1 (rs4704559 and rs4704560) were analyzed from the DNA isolated from peripheral blood. The allele and genotype frequencies in the PD-P and PD-NP groups were compared.

Results

Analysis of HOMER1 rs4704560 revealed a significant difference in both genotype and allele levels between PD-P and PD-NP groups. There was an overrepresentation of T-allele (42% vs. 16%; P < 0.001) and TT genotype (24% vs. 6%; P < 0.001) in the PD-P group compared to PD-NP group. There was no significant difference between PD-P and PD-NP groups when various genotypes and allele frequencies related to HOMER1 rs4704559 were compared.

Conclusion

PD-P is probably associated with overrepresentation of T-allele of HOMER1 rs4704560, and larger studies are warranted to confirm our results.

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.

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.

Fisetin Ameliorates Levodopa-Induced Dyskinesia in Experimental Model Parkinson's Disease: Role of Mitochondrial Activities and Monoamines Turnover

Background: Levodopa (or l-DOPA) is the current standard of care for the management of Parkinson's disease (PD), but its chronic administration has been associated with the development of LID (l-DOPA-induced dyskinesia). Fisetin is a dietary flavonoid known for its neuroprotective efficacy. Aim: To determine the neuroprotective potential of fisetin in 6-hydroxydopamine (6-OHDA)-lesioned LID animals. Methods: 6-OHDA (12 µg and L-ascorbic acid [10 µL]) was injected in a substantial nigra of Sprague-Dawley rat to develop PD followed by l-DOPA (20 mg/kg and benserazide HCl [5 mg/kg], 42 days) to induce LID. Rats were concomitantly administered with vehicle or amantadine (40 mg/kg), or fisetin (5, 10, and 25 mg/kg, p.o.) for 42 days with l-DOPA. Results: Chronic l-DOPA administration resulted in progressive abnormal involuntary movements (AIMs viz. axial, forelimb, and orolingual), akinesia (forelimb adjusting steps, FAS), muscular rigidity (catalepsy bar test), muscular coordination, and neurological impairments. Fisetin at doses of 10 and 25 mg/kg effectively reduced ( P < .05) these LID-induced AIMs and behavioral changes. Furthermore, fisetin treatment markedly ( P < .05) attenuated LID-induced diminished striatal mitochondrial complex activities, striatal monoamines (serotonin [5-HT] and dopamine [DA]), elevated monoamines turnover (DA: DOPAC and 5-HT: 5-HIAA). In addition, fisetin treatment effectively ( P < .05) reversed the upregulated expressions of striatal cFOS, FosB, Homer, Nurr-77, Parkin, and Pdyn. Conclusion: Our study demonstrated that fisetin offered neuroprotection via amelioration of striatum mitochondrial dysfunction and monoamine (5-HT and DA) turnover to halt further development of abnormal involuntary movement and dyskinesia.

Psychosis in Parkinson's Disease: A Lesson from Genetics

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

Plasticity, genetics, and epigenetics in l-dopa-induced dyskinesias

l-Dopa-induced dyskinesias (LIDs) are a frequent complication in l-dopa-treated patients affected by Parkinson's disease (PD). In the last years, several progresses in the knowledge of LIDs mechanisms have led to the identification of several molecular and electrophysiologic events. A complex cascade of intracellular events underlies the pathophysiology of LIDs, and, among these, aberrant plasticity in the cortico-basal ganglia system, at striatal and cortical level, plays a key role. Furthermore, several recent studies have investigated genetic susceptibility and epigenetic modifications in LIDs pathophysiology that might have future relevance in clinical practice and pharmacologic research. These progresses might lead to the development of specific strategies not only to treat, but also to prevent or delay the development of LIDs in PD.

New insights into pathogenesis of l-DOPA-induced dyskinesia

Parkinson's disease (PD) is a progressive and self-propelling neurodegenerative disorder, which is characterized by motor symptoms, such as rigidity, tremor, slowness of movement and problems with gait. These symptoms become worse over time. To date, Dopamine (DA) replacement therapy with 3, 4-dihydroxy-l-phenylalanine (L-DOPA) is still the most effective pharmacotherapy for motor symptoms of PD. Unfortunately, motor fluctuations consisting of wearing-off effect actions and dyskinesia tend to occur in a few years of starting l-DOPA. Currently, l-DOPA-induced dyskinesia (LID) is troublesome and the pathogenesis of LID requires further investigation. Importantly, a new intervention for LID is imminent. Thus, this review mainly summarized the clinical features, risk factors and pathogenesis of LID to provide updatefor the development of therapeutic targets and new approaches for the treatment of LID.

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.

Therapeutic Strategies to Treat or Prevent Off Episodes in Adults with Parkinson's Disease

Parkinson's disease is a chronic, neurodegenerative disease, which manifests with a mixture of motor, cognitive and behavioural symptoms. Levodopa is the most effective antiparkinsonian treatment to date, although chronic use engenders a mixture of complications in a substantial proportion of patients. Amongst these is the occurrence of episodes of worsening symptoms-'off' phenomena. These episodes can manifest with either motor or non-motor symptoms or a combination of these features and have been found to have profound impacts on patients' quality of life. Although preventative measures are poorly evidenced, avoiding excessive total daily levodopa intake in selected populations that are deemed to be of a higher risk for developing these episodes warrants further exploration. Methods to improve levodopa bioavailability and delivery to the brain are currently available and are of value in addressing these episodes once they have become established. These include modifications to levodopa formulations as well as the use of complimentary agents that improve levodopa bioavailability. The deployment of device-assisted approaches is a further dimension that can be considered in addressing these debilitating episodes. This review summarises the clinical manifestations of 'off' phenomena and the current approaches to treat them. Although we briefly discuss clinical advances on the horizon, the predominant focus is on existing, established treatments.

Modified Glutamatergic Postsynapse in Neurodegenerative Disorders

The postsynaptic density (PSD) is a complex subcellular domain important for postsynaptic signaling, function, and plasticity. The PSD is present at excitatory synapses and specialized to allow for precise neuron-to-neuron transmission of information. The PSD is localized immediately underneath the postsynaptic membrane forming a major protein network that regulates postsynaptic signaling and synaptic plasticity. Glutamatergic synaptic dysfunction affecting PSD morphology and signaling events have been described in many neurodegenerative disorders, either sporadic or familial forms. Thus, in this review we describe the main protein players forming the PSD and their activity, as well as relevant modifications in key components of the postsynaptic architecture occurring in Huntington's, Parkinson's and Alzheimer's diseases.

Influence of DRD1 and DRD3 Polymorphisms in the Occurrence of Motor Effects in Patients with Sporadic Parkinson's Disease

Parkinson's disease (PD) is a multisystem disorder that affects 2-3% of the population ≥ 65 years of age. The main pharmacologic agent use in the treatment of clinical symptoms of PD is levodopa (L-DOPA). However, the chronic use of L-DOPA might result in the emergence of motor complications such as motor fluctuation and dyskinesia. Previous studies have shown that the inter-individual variability and pharmacogenetic profile of PD patients seem to influence the occurrence of motor complications. For these reasons, the purpose of this study was to evaluate a possible relationship between DRD1 A48G and DRD3 Ser9Gly genetic variants with the occurrence of motor complications in PD patients in a Brazilian population. A total of 228 patients with idiopathic PD were enrolled. Patients were genotyped for DRD1 A48G and DRD3 Ser9Gly polymorphisms using PCR-RFLP. The univariate and multivariate analyses were performed to assess the association of these polymorphisms with the occurrence of motor fluctuation and dyskinesia in PD patients. Multiple Poisson regression analyses showed a protector effect to the occurrence of dyskinesia for individuals carrying of the DRD1 G/G genotype (PR 0.294; CI 0.09-0.87; p ≤ 0.020) after the threshold Bonferroni's. Besides, we verified risk increased to the occurrence of motor complications with daily L-DOPA dosage, disease duration, and users of rasagiline, selegiline, or entacapone (p < 0.05 for all). Our results suggest that the DRD1 A48G polymorphism and the presence of extrinsic and intrinsic factors may role an effect in the occurrence of dyskinesia in PD patients.

Pharmacogenetic Profile and the Occurrence of Visual Hallucinations in Patients With Sporadic Parkinson's Disease

Visual hallucinations are significant nonmotor symptoms in the course of treatment of Parkinson's disease. Previous studies have shown that the interindividual variability and pharmacogenetic profile of Parkinson's disease patients seem to influence the occurrence of visual hallucinations. In our study, we investigated a possible relationship of sequence variants in DRD1, DRD2, DRD3, DAT1, and COMT genes with the presence of visual hallucinations in Parkinson's disease patients. A total of 224 Brazilian patients from the Pro-Parkinson service at the Clinical Hospital of the University of Pernambuco, diagnosed with sporadic Parkinson's disease, were enrolled. Parkinson's disease patients were divided into 2 groups based on the presence or absence of visual hallucinations. The sequence variants for DRD1, DRD2, DRD3, DAT1, and COMT were determined through the polymerase chain reaction-restriction fragment length polymorphism technique. Multiple Poisson regression analyses showed that individuals carrying the DRD3 Ser/Ser and Ser/Gly genotypes presented increased prevalence ratios of visual hallucinations (9.7-fold and 4.4-fold, respectively; P < .001). Regarding DAT1 rs28363170, there was a 9.82-fold increase in the prevalence ratio in patients with the 10/11 genotype, 8.78-fold for the 10/8 genotype, and 2.44-fold for the 9/8 genotypes (P < .001, for all). In addition, visual hallucinations were also associated with use of transdermal patches with rotigotine (PR, 3.7; 95%CI, 1.2-10.9; P = .017) and rasagiline (PR, 2.8; 95%CI, 1.3-6.0; P = .006). Our results suggest that the genetic variants DRD3 and DAT1, along with other therapeutic confounders, may influence the prevalence ratio of visual hallucinations.

Levodopa-induced dyskinesia: clinical features, incidence, and risk factors

Symptoms of Parkinson's disease have been controlled with levodopa for many years; however, motor complications consisting of wearing off of medication effect and dyskinesias tend to occur within a few years of starting levodopa. Motor complications can begin a few months after taking levodopa, with the average time to onset estimated to be 6.5 years. Dyskinesias can be troublesome and require intervention. Levodopa-induced dyskinesia can be composed of a variety of movement disorders including chorea, dystonia, ballism, myoclonus, and akathisia. Based on the clinical pattern, the most common dyskinesia is chorea and choreoathetosis. The clinical manifestations can be divided into three main categories based on their clinical movement patterns and the temporal correlation between the occurrence of dyskinesia and the levodopa dosing: on or peak-dose dyskinesias, biphasic dyskinesias, and Off dyskinesias. Severe cases of dyskinesia have been reported, with the extreme being dyskinesia-hyperpyrexia syndrome. The prevalence of LID has been reported in many studies, but the reported incidence varies. The rate of LID development is from 3 to 94%. The prevalence of LID mainly depends on age at onset, disease duration, and severity, and duration of levodopa therapy. Some of the risk factors for the development of dyskinesia are modifiable. Modifiable risk factors include levodopa dose and body weight. Non-modifiable risk factors include age, gender, duration of disease, clinical subtype, disease progression, disease severity, and genetic factors.

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

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

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

Background

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

Results

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

Conclusion

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

Electronic supplementary material

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

Parkinson's Disease: From Pathogenesis to Pharmacogenomics

Parkinson's disease (PD) is the second most important age-related neurodegenerative disorder in developed societies, after Alzheimer's disease, with a prevalence ranging from 41 per 100,000 in the fourth decade of life to over 1900 per 100,000 in people over 80 years of age. As a movement disorder, the PD phenotype is characterized by rigidity, resting tremor, and bradykinesia. Parkinson's disease -related neurodegeneration is likely to occur several decades before the onset of the motor symptoms. Potential risk factors include environmental toxins, drugs, pesticides, brain microtrauma, focal cerebrovascular damage, and genomic defects. Parkinson's disease neuropathology is characterized by a selective loss of dopaminergic neurons in the substantia nigra pars compacta, with widespread involvement of other central nervous system (CNS) structures and peripheral tissues. Pathogenic mechanisms associated with genomic, epigenetic and environmental factors lead to conformational changes and deposits of key proteins due to abnormalities in the ubiquitin-proteasome system together with dysregulation of mitochondrial function and oxidative stress. Conventional pharmacological treatments for PD are dopamine precursors (levodopa, l-DOPA, l-3,4 dihidroxifenilalanina), and other symptomatic treatments including dopamine agonists (amantadine, apomorphine, bromocriptine, cabergoline, lisuride, pergolide, pramipexole, ropinirole, rotigotine), monoamine oxidase (MAO) inhibitors (selegiline, rasagiline), and catechol-O-methyltransferase (COMT) inhibitors (entacapone, tolcapone). The chronic administration of antiparkinsonian drugs currently induces the "wearing-off phenomenon", with additional psychomotor and autonomic complications. In order to minimize these clinical complications, novel compounds have been developed. Novel drugs and bioproducts for the treatment of PD should address dopaminergic neuroprotection to reduce premature neurodegeneration in addition to enhancing dopaminergic neurotransmission. Since biochemical changes and therapeutic outcomes are highly dependent upon the genomic profiles of PD patients, personalized treatments should rely on pharmacogenetic procedures to optimize therapeutics.

The psychosis spectrum in Parkinson disease

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

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

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

A glutamatergic network mediates lithium response in bipolar disorder as defined by epigenome pathway analysis

AIM

A regulatory network in the human brain mediating lithium response in bipolar patients was revealed by analysis of functional SNPs from genome-wide association studies (GWAS) and published gene association studies, followed by epigenome mapping.

METHODS

An initial set of 23,312 SNPs in linkage disequilibrium with lead SNPs, and sub-threshold GWAS SNPs rescued by pathway analysis, were studied in the same populations. These were assessed using our workflow and annotation by the epigenome roadmap consortium.

RESULTS

Twenty-seven percent of 802 SNPs that were associated with lithium response (13 published studies gene association studies and two GWAS) were shared in common with 1281 SNPs from 18 GWAS examining psychiatric disorders and adverse events associated with lithium treatment. Nineteen SNPs were annotated as active regulatory elements such as enhancers and promoters in a tissue-specific manner. They were located within noncoding regions of ten genes: ANK3, ARNTL, CACNA1C, CACNG2, CDKN1A, CREB1, GRIA2, GSK3B, NR1D1 and SLC1A2. Following gene set enrichment and pathway analysis, these genes were found to be significantly associated (p = 10(-27); Fisher exact test) with an AMPA2 glutamate receptor network in human brain. Our workflow results showed concordance with annotation of regulatory elements from the epigenome roadmap. Analysis of cognate mRNA and enhancer RNA exhibited patterns consistent with an integrated pathway in human brain.

CONCLUSION

This pharmacoepigenomic regulatory pathway is located in the same brain regions that exhibit tissue volume loss in bipolar disorder. Although in silico analysis requires biological validation, the approach provides value for identification of candidate variants that may be used in pharmacogenomic testing to identify bipolar patients likely to respond to lithium.

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.

Is there a role for ADORA2A polymorphisms in levodopa-induced dyskinesia in Parkinson's disease patients?

AIM

Levodopa is first line treatment of Parkinson's disease (PD). However, its use is associated with the presence of motor fluctuations and dyskinesias. In recent years, adenosine A2A receptor (A2AR) is rising as a therapeutic target for PD. The aim of the present study was to investigate whether ADORA2A is associated with levodopa adverse effects.

PATIENTS & METHODS

Two hundred and eight PD patients on levodopa therapy were investigated. rs2298383 and rs3761422 at the ADORA2A gene were genotyped by allelic discrimination assays.

RESULTS

A trend for association was observed for both polymorphism and diplotypes with dyskinesia.

CONCLUSION

The present results should be considered as positive preliminary evidence. Further studies are needed to determine the association between ADORA2A and dyskinesia. Original submitted 3 December 2014; Revision submitted 13 February 2015.

Clinical spectrum of levodopa-induced complications

The first years of Parkinson disease (PD) treatment are marked by good and sustained responses to dopaminergic therapy. With disease progression and longer exposure to levodopa (l-dopa), patients develop a range of l-dopa-induced complications that include motor and non-motor symptoms. Motor complications include motor fluctuations, characterized by periods of reduced benefit from the medication, and l-dopa-induced dyskinesia, characterized by emergence of hyperkinetic involuntary movements. Dyskinesia can occur at peak effect of l-dopa, at the beginning and end of dose, or between doses. These motor complications are often associated with fluctuations in non-motor symptoms, particularly fluctuations in neuropsychiatric, autonomic, and sensory symptoms. Recognizing such complications and understanding their relationship with the timing of l-dopa doses is essential for adequate diagnosis and management. Society.