The RIT2 and STX1B polymorphisms are associated with Parkinson's disease

Joint-tissue integrative analysis identifies high-risk genes for Parkinson's disease

The loss of dopaminergic neurons in the substantia nigra and the abnormal accumulation of synuclein proteins and neurotransmitters in Lewy bodies constitute the primary symptoms of Parkinson's disease (PD). Besides environmental factors, scholars are in the early stages of comprehending the genetic factors involved in the pathogenic mechanism of PD. Although genome-wide association studies (GWAS) have unveiled numerous genetic variants associated with PD, precisely pinpointing the causal variants remains challenging due to strong linkage disequilibrium (LD) among them. Addressing this issue, expression quantitative trait locus (eQTL) cohorts were employed in a transcriptome-wide association study (TWAS) to infer the genetic correlation between gene expression and a particular trait. Utilizing the TWAS theory alongside the enhanced Joint-Tissue Imputation (JTI) technique and Mendelian Randomization (MR) framework (MR-JTI), we identified a total of 159 PD-associated genes by amalgamating LD score, GTEx eQTL data, and GWAS summary statistic data from a substantial cohort. Subsequently, Fisher's exact test was conducted on these PD-associated genes using 5,152 differentially expressed genes sourced from 12 PD-related datasets. Ultimately, 29 highly credible PD-associated genes, including CTX1B, SCNA, and ARSA, were uncovered. Furthermore, GO and KEGG enrichment analyses indicated that these genes primarily function in tissue synthesis, regulation of neuron projection development, vesicle organization and transportation, and lysosomal impact. The potential PD-associated genes identified in this study not only offer fresh insights into the disease's pathophysiology but also suggest potential biomarkers for early disease detection.

Silencing Parkinson's risk allele Rit2 sex-specifically compromises motor function and dopamine neuron viability

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and arises from dopamine (DA) neuron death selectively in the substantia nigra pars compacta (SNc). Rit2 is a reported PD risk allele, and recent single cell transcriptomic studies identified a major RIT2 cluster in PD DA neurons, potentially linking Rit2 expression loss to a PD patient cohort. However, it is still unknown whether Rit2 loss itself impacts DA neuron function and/or viability. Here we report that conditional Rit2 silencing in mouse DA neurons drove motor dysfunction that occurred earlier in males than females and was rescued at early stages by either inhibiting the DA transporter (DAT) or with L-DOPA treatment. Motor dysfunction was accompanied by decreased DA release, striatal DA content, phenotypic DAergic markers, DA neurons, and DAergic terminals, with increased pSer129-alpha synuclein and pSer935-LRRK2 expression. These results provide clear evidence that Rit2 loss is causal for SNc cell death and motor dysfunction, and reveal key sex-specific differences in the response to Rit2 loss.

Rit2 silencing in dopamine neurons drives a Parkinsonian phenotype

Parkinson's disease (PD) is the second most prevalent neurodegenerative disease and arises from dopamine (DA) neuron death selectively in the substantia nigra pars compacta (SNc). Rit2 is a reported PD risk allele, and recent single cell transcriptomic studies identified a major RIT2 cluster in PD DA neurons, potentially linking Rit2 expression loss to a PD patient cohort. However, it is still unknown whether Rit2 loss itself is causative for PD or PD-like symptoms. Here we report that conditional Rit2 silencing in mouse DA neurons drove motor dysfunction that occurred earlier in males than females and was rescued at early stages by either inhibiting the DA transporter (DAT) or with L-DOPA treatment. Motor dysfunction was accompanied by decreased DA release, striatal DA content, phenotypic DAergic markers, DA neurons, and DAergic terminals, with increased pSer129-alpha synuclein and pSer935-LRRK2 expression. These results provide the first evidence that Rit2 loss is causal for SNc cell death and a PD-like phenotype, and reveal key sex-specific differences in the response to Rit2 loss.

An antisense Alu transposon insertion/deletion polymorphism of ALDH1A1 may functionally associate with Parkinson's disease

BACKGROUND

Aldehyde dehydrogenase 1 (encoded by ALDH1A1) has been shown to protect against Parkinson's disease (PD) by reducing toxic metabolites of dopamine. We herein revealed an antisense Alu element insertion/deletion polymorphism in intron 4 of ALDH1A1, and hypothesized that it might play a role in PD.  METHODS: A Han Chinese cohort comprising 488 PD patients and 515 controls was recruited to validate the Alu insertion/deletion polymorphism following a previous study of tag-single nucleotide polymorphisms, where rs7043217 was shown to be significantly associated with PD. Functional analyses of the Alu element insertion were performed.

RESULTS

The Alu element of ALDH1A1 was identified to be a variant of Yb8 subfamily and termed as Yb8c4. The antisense Yb8c4 insertion/deletion polymorphism (named asYb8c4^ins and asYb8c4^del, respectively) appeared to be in a complete linkage disequilibrium with rs7043217 and was validated to be significantly associated with PD susceptibility with asYb8c4^ins serving as a risk allele (P = 0.030, OR = 1.224, 95% CI = 1.020-1.470). Multiple functional analyses including ALDH1A1 mRNA expression in blood cells of carriers, and reporters of EGFP and luciferase showed that the asYb8c4^ins had a suppressive activity on gene transcription. Mechanistic explorations suggested that the asYb8c4^ins induced no changes in CpG methylation and mRNA splicing of ALDH1A1 and appeared no binding of transcription factors.

CONCLUSIONS

Our results consolidate an involvement of ALDH1 in PD pathogenesis. The asYb8c4 polymorphism may be a functional output of its linkage disequilibrium-linked single nucleotide polymorphisms.

Dynamic control of the dopamine transporter in neurotransmission and homeostasis

The dopamine transporter (DAT) transports extracellular dopamine into the intracellular space contributing to the regulation of dopamine neurotransmission. A reduction of DAT density is implicated in Parkinson's disease (PD) by neuroimaging; dopamine turnover is dopamine turnover is elevated in early symptomatic PD and in presymptomatic individuals with monogenic mutations causal for parkinsonism. As an integral plasma membrane protein, DAT surface expression is dynamically regulated through endocytic trafficking, enabling flexible control of dopamine signaling in time and space, which in turn critically modulates movement, motivation and learning behavior. Yet the cellular machinery and functional implications of DAT trafficking remain enigmatic. In this review we summarize mechanisms governing DAT trafficking under normal physiological conditions and discuss how PD-linked mutations may disturb DAT homeostasis. We highlight the complexity of DAT trafficking and reveal DAT dysregulation as a common theme in genetic models of parkinsonism.

The cis-Regulatory Element of SNCA Intron 4 Modulates Susceptibility to Parkinson's Disease in Han Chinese

Objective: A novel functional cis-regulatory element (CRE) located at SNCA intron 4 has recently been identified in association with Parkinson's disease (PD) risk in European descendants. We aimed to investigate whether this CRE is associated with PD in Han Chinese ethnicity. Methods: A Chinese cohort comprising 513 sporadic PD patients and 517 controls was recruited. CRE variants were identified by sequencing and then analyzed. Results: A total of nine variants were detected, namely eight single nucleotide variants and one new insertion variant. Two variants, rs17016188 and rs7684892, had minor allele frequency greater than 5%. A difference of rs17016188 was observed in males with the C allele serving as a recessive risk factor (p = 0.001, OR = 2.349, 95% CI = 1.414-3.901) following Bonferroni correction. Haplotypes of rs17016188 and rs7684892 showed distribution differences in the total and the male populations (p = 0.002 and 4.08 × 10^-5, respectively). Among the haplotypes, rs17016188/T-rs7684892/G was associated with a reduced risk for PD (p = 4.8 × 10^-4, OR = 0.731, 95% CI = 0.614-0.872). Conclusions: Our results provide insight into how the SNCA intron 4 CRE harbors variants and its contribution to PD risk in Chinese ethnicity.

Association of RIT2 and RAB7L1 with Parkinson's disease: a case-control study in a Taiwanese cohort and a meta-analysis in Asian populations

Several genome-wide association studies and meta-analyses on Parkinson's disease (PD)-related genes have identified several risk foci in Ras-related genes, particularly among Caucasian individuals. However, the corresponding results have been controversial among Asian individuals. We investigated whether 2 single-nucleotide polymorphisms of Ras-related genes, RIT2 (rs12456492) and RAB7L1 (rs823118), are associated with PD risk in Taiwanese individuals. In addition, we conducted a meta-analysis of all studies related to rs12456492 in Asian populations to resolve inconsistency in this locus. In total, 1103 Taiwanese individuals (588 patients with PD and 515 controls) and 1111 Taiwanese individuals (594 patients with PD and 517 controls) were genotyped for rs12456492 and rs823118. However, we could not confirm the association of rs12456492 and rs823118 with PD. Our current meta-analysis involving the rs12456492(A/G) variant demonstrated that the GG + GA genotypes, GG genotypes, and G allele may be risk factors for PD. RIT2 may increase PD risk in Asian individuals. The discrepancies between Caucasian and Asian populations may be due to differences in geographic region-specific genetic backgrounds and gene-environmental interactions.

STXBP1 encephalopathy

De novo pathogenic variants in STXBP1 encoding syntaxin1-binding protein (STXBP1, also known as Munc18-1) lead to a range of early-onset neurocognitive conditions, most commonly early infantile epileptic encephalopathy type 4 (EIEE4, also called STXBP1 encephalopathy), a severe form of epilepsy associated with developmental delay/intellectual disability. Other neurologic features include autism spectrum disorder and movement disorders. The progression of neurologic symptoms has been reported in a few older affected individuals, with the appearance of extrapyramidal features, reminiscent of early onset parkinsonism. Understanding the pathologic process is critical to improving therapies, as currently available antiepileptic drugs have shown limited success in controlling seizures in EIEE4 and there is no precision medication approach for the other neurologic features of the disorder. Basic research shows that genetic knockout of STXBP1 or other presynaptic proteins of the exocytic machinery leads to widespread perinatal neurodegeneration. The mechanism that regulates this effect is under scrutiny but shares intriguing hallmarks with classical neurodegenerative diseases, albeit appearing early during brain development. Most critically, recent evidence has revealed that STXBP1 controls the self-replicating aggregation of α-synuclein, a presynaptic protein involved in various neurodegenerative diseases that are collectively known as synucleinopathies, including Parkinson disease. In this review, we examine the tantalizing link among STXBP1 function, EIEE, and the neurodegenerative synucleinopathies, and suggest that neural development in EIEE could be further affected by concurrent synucleinopathic mechanisms.

Polymorphisms of ACMSD-TMEM163, MCCC1, and BCKDK-STX1B Are Not Associated with Parkinson's Disease in Taiwan

Previous genome-wide association studies in Caucasian populations suggest that genetic loci in amino acid catabolism may be associated with Parkinson's disease (PD). However, these genetic disease associations were limitedly reported in Asian populations. Herein, we investigated the effect of top three PD-associated genetic variants related to amino acid catabolism in Caucasians listed on the top risk loci identified by meta-analysis of genome-wide association studies in PDGene database, including aminocarboxymuconate-semialdehyde decarboxylase- (ACMSD-) transmembrane protein 163 (TMEM163) rs6430538, methylcrotonyl-CoA carboxylase 1 (MCCC1) rs12637471, and branched-chain ketoacid dehydrogenase kinase- (BCKDK-) syntaxin 1B (STX1B) rs14235, by genotyping 599 Taiwanese patients with PD and 598 age-matched control subjects. PD patients demonstrate similar allelic and genotypic frequencies in all tested genetic variants. These ethnic discrepancies of genetic variants suggest a distinct genetic background of amino acid catabolism between Taiwanese and Caucasian PD patients.

The Prion Protein Regulates Synaptic Transmission by Controlling the Expression of Proteins Key to Synaptic Vesicle Recycling and Exocytosis

The cellular prion protein (PrP^C), whose misfolded conformers are implicated in prion diseases, localizes to both the presynaptic membrane and postsynaptic density. To explore possible molecular contributions of PrP^C to synaptic transmission, we utilized a mass spectrometry approach to quantify the release of glutamate from primary cerebellar granule neurons (CGN) expressing, or deprived of (PrP-KO), PrP^C, following a depolarizing stimulus. Under the same conditions, we also tracked recycling of synaptic vesicles (SVs) in the two neuronal populations. We found that in PrP-KO CGN these processes decreased by 40 and 60%, respectively, compared to PrP^C-expressing neurons. Unbiased quantitative mass spectrometry was then employed to compare the whole proteome of CGN with the two PrP genotypes. This approach allowed us to assess that, relative to the PrP^C-expressing counterpart, the absence of PrP^C modified the protein expression profile, including diminution of some components of SV recycling and fusion machinery. Subsequent quantitative RT-PCR closely reproduced proteomic data, indicating that PrP^C is committed to ensuring optimal synaptic transmission by regulating genes involved in SV dynamics and neurotransmitter release. These novel molecular and cellular aspects of PrP^C add insight into the underlying mechanisms for synaptic dysfunctions occurring in neurodegenerative disorders in which a compromised PrP^C is likely to intervene.

Neuroepigenetics of Aging and Age-Related Neurodegenerative Disorders

Neurodegenerative diseases are complex, progressive disorders and affect millions of people worldwide, contributing significantly to the global burden of disease. In recent years, research has begun to investigate epigenetic mechanisms for a potential role in disease etiology. In this chapter, we describe the current state of play for epigenetic research into neurodegenerative disorders including Alzheimer's disease, Parkinson's disease and Huntington's disease. We focus on the recent evidence for a potential role of DNA modifications, histone modifications and non-coding RNA in the etiology of these disorders. Finally, we discuss how new technological and bioinformatics advances in the field of epigenetics could further progress our understanding about the underlying mechanisms of neurodegenerative diseases.

Age-related epigenetic changes in hippocampal subregions of four animal models of Alzheimer's disease

Both aging and Alzheimer's disease (AD) are associated with widespread epigenetic changes, with most evidence suggesting global hypomethylation in AD. It is, however, unclear how these age-related epigenetic changes are linked to molecular aberrations as expressed in animal models of AD. Here, we investigated age-related changes of epigenetic markers of DNA methylation and hydroxymethylation in a range of animal models of AD, and their correlations with amyloid plaque load. Three transgenic mouse models, including the J20, APP/PS1dE9 and 3xTg-AD models, as well as Caribbean vervets (a non-transgenic non-human primate model of AD) were investigated. In the J20 mouse model, an age-related decrease in DNA methylation was found in the dentate gyrus (DG) and a decrease in the ratio between DNA methylation and hydroxymethylation was found in the DG and cornu ammonis (CA) 3. In the 3xTg-AD mice, an age-related increase in DNA methylation was found in the DG and CA1-2. No significant age-related alterations were found in the APP/PS1dE9 mice and non-human primate model. In the J20 model, hippocampal plaque load showed a significant negative correlation with DNA methylation in the DG, and with the ratio a negative correlation in the DG and CA3. For the APP/PS1dE9 model a negative correlation between the ratio and plaque load was observed in the CA3, as well as a negative correlation between DNA methyltransferase 3A (DNMT3A) levels and plaque load in the DG and CA3. Thus, only the J20 model showed an age-related reduction in global DNA methylation, while DNA hypermethylation was observed in the 3xTg-AD model. Given these differences between animal models, future studies are needed to further elucidate the contribution of different AD-related genetic variation to age-related epigenetic changes.

Genome-wide Pleiotropy Between Parkinson Disease and Autoimmune Diseases

Importance

Recent genome-wide association studies (GWAS) and pathway analyses supported long-standing observations of an association between immune-mediated diseases and Parkinson disease (PD). The post-GWAS era provides an opportunity for cross-phenotype analyses between different complex phenotypes.

Objectives

To test the hypothesis that there are common genetic risk variants conveying risk of both PD and autoimmune diseases (ie, pleiotropy) and to identify new shared genetic variants and their pathways by applying a novel statistical framework in a genome-wide approach.

Design, Setting, and Participants

Using the conjunction false discovery rate method, this study analyzed GWAS data from a selection of archetypal autoimmune diseases among 138 511 individuals of European ancestry and systemically investigated pleiotropy between PD and type 1 diabetes, Crohn disease, ulcerative colitis, rheumatoid arthritis, celiac disease, psoriasis, and multiple sclerosis. NeuroX data (6927 PD cases and 6108 controls) were used for replication. The study investigated the biological correlation between the top loci through protein-protein interaction and changes in the gene expression and methylation levels. The dates of the analysis were June 10, 2015, to March 4, 2017.

Main Outcomes and Measures

The primary outcome was a list of novel loci and their pathways involved in PD and autoimmune diseases.

Results

Genome-wide conjunctional analysis identified 17 novel loci at false discovery rate less than 0.05 with overlap between PD and autoimmune diseases, including known PD loci adjacent to GAK, HLA-DRB5, LRRK2, and MAPT for rheumatoid arthritis, ulcerative colitis and Crohn disease. Replication confirmed the involvement of HLA, LRRK2, MAPT, TRIM10, and SETD1A in PD. Among the novel genes discovered, WNT3, KANSL1, CRHR1, BOLA2, and GUCY1A3 are within a protein-protein interaction network with known PD genes. A subset of novel loci was significantly associated with changes in methylation or expression levels of adjacent genes.

Conclusions and Relevance

The study findings provide novel mechanistic insights into PD and autoimmune diseases and identify a common genetic pathway between these phenotypes. The results may have implications for future therapeutic trials involving anti-inflammatory agents.

Ras-like without CAAX 2 (RIT2): a susceptibility gene for autism spectrum disorder

Ras-like without CAAX2 (RIT2) which encodes a GTP-binding protein has recently been reported as a new susceptibility gene for Autism Spectrum Disorders (ASD) in a genome-wide association study. Since the gene is suggested to be involved in the pathogenesis of different neurological diseases, we investigated the association of two single nucleotide polymorphisms (SNP) rs16976358 and rs4130047 of this gene with ASD in Iranian patients. A total of 1004 individuals, comprising 532 ASD cases and 472 healthy subjects participated in this study. Allele frequency analyses showed significant over-presentation of rs16976358-C allele in cases versus controls (P < 0.0001). In addition, rs16976358 CC genotype (OR (95% CI) =3.57(1.72-7.69) and P < 0.0001) and rs4130047 CC genotype (OR (95% CI) =0.64(0.43-0.97) and P = 0.035) were associated with ASD in recessive inheritance model. Besides, haplotype analysis demonstrated an association between the C/T haplotype block (rs16976358/rs4130047) and ASD (OR (95%CI) = 0.44 (0.31-0.62), P < 0.0001). Altogether, our findings provided additional confirmation for the RIT2 gene participation in ASD risk and suggested the rs16976358 variant as a possible genetic risk factor for this disorder.

The role of Ca2+ signaling in Parkinson's disease

Across all kingdoms in the tree of life, calcium (Ca2+) is an essential element used by cells to respond and adapt to constantly changing environments. In multicellular organisms, it plays fundamental roles during fertilization, development and adulthood. The inability of cells to regulate Ca2+ can lead to pathological conditions that ultimately culminate in cell death. One such pathological condition is manifested in Parkinson's disease, the second most common neurological disorder in humans, which is characterized by the aggregation of the protein, α-synuclein. This Review discusses current evidence that implicates Ca2+ in the pathogenesis of Parkinson's disease. Understanding the mechanisms by which Ca2+ signaling contributes to the progression of this disease will be crucial for the development of effective therapies to combat this devastating neurological condition.

Polymorphism in MIR4697 but not VPS13C, GCH1, or SIPA1L2 is associated with risk of Parkinson's disease in a Han Chinese population

A large meta-analysis recently identified six new loci associated with risk of PD, but subsequent studies have given discrepant results. Here we conducted a case-control study in a Han Chinese population in an attempt to clarify risk associations in Chinese. Among the four single-nucleotide polymorphisms (SNPs) that we examined - VPS13C-rs2414739, MIR4697-rs329648, GCH1-rs11158026, and SIPA1L2- rs10797576 we detected a significant association between rs329648 and risk of developing PD in a recessive model. This association remained significant after adjusting for gender and age (OR 1.87, 95%CI 1.295-2.694, p=8.21×10^-4) or Bonferroni correction. The T allele of rs329648 occurred significantly more frequently among patients with PD than among healthy controls (OR 1.22, 95%CI 1.033-1.443, p=0.02), while there was no statistic significant after Bonferroni correction. Subgroup analysis showed a significant association specifically among males in a recessive model (OR 1.943, 95%CI 1.200-3.147, p=0.007). In contrast, genotye and allele frequencies at rs329648 did not differ significantly between female patients with PD and healthy female controls, or between patients with early-onset or late-onset PD. Our results suggest that rs329648 is associated with risk of developing PD in the Han Chinese population. Our findings should be verified in further studies, and they highlight the need for functional studies of MIR4697.

Exploring Approaches for Detecting Protein Functional Similarity within an Orthology-based Framework

Protein functional similarity based on gene ontology (GO) annotations serves as a powerful tool when comparing proteins on a functional level in applications such as protein-protein interaction prediction, gene prioritization, and disease gene discovery. Functional similarity (FS) is usually quantified by combining the GO hierarchy with an annotation corpus that links genes and gene products to GO terms. One large group of algorithms involves calculation of GO term semantic similarity (SS) between all the terms annotating the two proteins, followed by a second step, described as “mixing strategy”, which involves combining the SS values to yield the final FS value. Due to the variability of protein annotation caused e.g. by annotation bias, this value cannot be reliably compared on an absolute scale. We therefore introduce a similarity z-score that takes into account the FS background distribution of each protein. For a selection of popular SS measures and mixing strategies we demonstrate moderate accuracy improvement when using z-scores in a benchmark that aims to separate orthologous cases from random gene pairs and discuss in this context the impact of annotation corpus choice. The approach has been implemented in Frela, a fast high-throughput public web server for protein FS calculation and interpretation.

Systematic analysis of genetic variants in Han Chinese patients with sporadic Parkinson's disease

Parkinson's disease (PD) is one of the most common neurodegenerative disorders. Accumulated evidence confirms that genetic factors play a considerable role in PD pathogenesis. To examine whether point variants or haplotypes are associated with PD development, genotyping of 35 variants in 22 PD-related genes was performed in a well-characterized cohort of 512 Han Chinese PD patients and 512 normal controls. Both Pearson's χ2 test and haplotype analysis were used to evaluate whether variants or their haplotypes were associated with PD in this cohort. The only statistically significant differences in genotypic and allelic frequencies between the patients and the controls were in the DnaJ heat shock protein family (Hsp40) member C10 gene (DNAJC10) variant rs13414223 (P = 0.004 and 0.002, respectively; odds ratio = 0.652, 95% confidence interval: 0.496-0.857). No other variants or haplotypes exhibited any significant differences between these two groups (all corrected P > 0.05). Our findings indicate that the variant rs13414223 in the DNAJC10 gene, a paralog of PD-related genes DNAJC6 and DNAJC13, may play a protective role in PD. This suggests it may be a PD-associated gene.

Advances in understanding genomic markers and pharmacogenetics of Parkinson's disease

INTRODUCTION

The inheritance pattern of Parkinson's disease (PD) is likely multifactorial (owing to the interplay of genetic predisposition and environmental factors). Many pharmacogenetic studies have tried to establish a possible role of candidate genes in PD risk. Several studies have focused on the influence of genes in the response to antiparkinsonian drugs and in the risk of developing side-effects of these drugs.

AREAS COVERED

This review presents an overview of current knowledge, with particular emphasis on the most recent advances, both in case-control association studies on the role of candidate genes in the risk for PD as well as pharmacogenetic studies on the role of genes in the development of side effects of antiparkinsonian drugs. The most reliable results should be derived from meta-analyses of case-control association studies on candidate genes involving large series of PD patients and controls, and from genome-wide association studies (GWAS).

EXPERT OPINION

Prospective studies of large samples involving several genes with a detailed history of exposure to environmental factors in the same cohort of subjects, should be useful to clarify the role of genes in the risk for PD. The results of studies on the role of genes in the development of side-effects of antiparkinsonian drugs should, at this stage, only be considered preliminary.

No association of FAM47E rs6812193, SCARB2 rs6825004 and STX1B rs4889603 polymorphisms with Parkinson's disease in a Chinese Han population

Recently, a series of studies found that the single-nucleotide polymorphisms (SNPs) rs6812193 in the family with sequence similarity 47, member E (FAM47E), rs6825004 in the scavenger receptor class B member 2 (SCARB2) and rs4889603 in the Syntaxin1B (STX1B) genes increase the risk for Parkinson's disease (PD). However, the results of subsequent independent studies were inconsistent. To explore the associations between the three SNPs and PD in the Chinese population, a large cohort was analyzed in a case-control study. A total of 1994 subjects, including 1179 PD and 815 healthy controls (HCs), were investigated. All subjects were genotyped for rs6812193, rs6825004 and rs4889603 using the Sequenom iPLEX Assay. There was no significant difference in additive genetic model of rs6812193, rs6825004 and rs4889603 between PD and controls, even after being stratified by sex and age. In addition, no significant differences were found between other subgroups of PD patients with regard to clinical presentation. Our findings suggested that FAM47E rs6812193, SCARB2 rs6825004 and STX1B rs4889603 do not confer a significant risk for PD in Chinese population.

Genetic association of RIT2 rs12456492 polymorphism and Parkinson's disease susceptibility in Asian populations: a meta-analysis

Recent studies investigating the association of the Ras-like without CAAX 2 (RIT2) polymorphism, rs12456492, with Parkinson’s disease (PD) are controversial. We performed a meta-analysis to study the association between rs12456492 and PD susceptibility in Asian populations. Literature searches of PubMed and Embase were performed up to June 3, 2015, and the strength of the association between rs12456492 and PD was evaluated by odds ratios (OR) and 95% confidence intervals (CI). Four studies conducted between 2013 and 2015, comprising 2017 PD cases and 2010 controls, were included in the meta-analysis. Significant association of rs12456492 with PD was found in the dominant (GG + AG vs. AA: OR = 1.26, 95% CI = 1.20–1.44, P = 0.00) and additive models (GG vs. AA: OR = 1.38, 95% CI = 1.03–1.83, P = 0.030). Although sensitivity analysis found that the overall result was stable only in the dominant genetic model, a publication bias was also detected. Therefore, the results should be treated with caution. The current meta-analysis suggested that rs12456492 might be associated with increased PD risk in Asian populations, but studies using larger sample sizes and different ethnic populations will be needed to further confirm this association.