Genetic Variants in GAPDH Confer Susceptibility to Sporadic Parkinson’s Disease in a Chinese Han Population

Background

Accumulating evidence has demonstrated that the glyceraldehyde-3-phosphate dehydrogenase (GAPDH) is a part of Lewy body inclusions and involves the pathogenesis of Parkinson’s disease (PD). However, it remains unknown whether or not genetic variation at the GAPDH locus contributes to the risk for PD.

Methods

A total of 302 sporadic PD patients and 377 control subjects were recruited in our study for assessing two single nucleotide polymorphisms (rs3741918 and rs1060619) in the GAPDH gene. Both allelic association and additive models were used to analyze association between GAPDH variants and risk for PD.

Results

Both polymorphisms were significantly associated with risk for PD after correction by Bonferroni multiple testing. The minor allele of rs3741918 was associated with decreased risk of sporadic PD (allelic contrast, OR = 0.74, 95% CI: 0.59–0.93, corrected P = 0.028; additive model, OR = 0.73, 95% CI: 0.58–0.92, corrected P = 0.018). While for the rs1060619 locus, the minor allele conferred increased risk for PD (allelic contrast, OR = 1.41, 95% CI: 1.14–1.75, corrected P = 0.007; additive model, OR = 1.43, 95% CI: 1.15–1.79, corrected P = 0.002).

Conclusion

Our study indicates that GAPDH variants confer susceptibility to sporadic PD in a Chinese Han population, which is consistent with the role of GAPDH protein in neuronal apoptosis. To our knowledge, this is the first study of genetic association between GAPDH locus and risk for PD in the Chinese population.     

HLA-DRB1 Alleles Are Associated with the Susceptibility to Sporadic Parkinson’s Disease in Chinese Han Population

Immune disorders may play an important role in the pathogenesis of Parkinson''s disease (PD). Recently, polymorphisms in the HLA-DR region have been found to be associated with sporadic PD in European ancestry populations. However, polymorphisms in the HLA complex are highly variable with ethnic and geographic origin. To explore the relationships between polymorphisms of the HLA-DR region and sporadic PD in Chinese Han population, we genotyped 567 sporadic PD patients and 746 healthy controls in two independent series for the HLA-DRB1 locus with Polymerase chain reaction-sequence based typing(PCR-SBT). The χ² test was used to evaluate the distribution of allele frequencies between the patients and healthy controls. The impact of HLA-DRB1 alleles on PD risk was estimated by unconditional logistic regression. We found a significant higher frequency of HLA-DRB1*0301 in sporadic PD patients than in healthy controls and a positive association, which was independent of onset age, between HLA-DRB1*0301 and PD risk. Conversely, a lower frequency of HLA-DRB1*0406 was found in sporadic PD patients than in healthy controls, with a negative association between HLA-DRB1*0406 and PD risk. Furthermore, a meta-analysis involving 195205 individuals was conducted to summarize the frequencies of these two alleles in populations from various ethnic regions, we found a higher frequency of HLA-DRB1*0301, but a lower frequency of HLA-DRB1*0406 in European ancestry populations than that in Asians, this was consistent with the higher prevalence of sporadic PD in European ancestry populations. Based on these results, we speculate that HLA-DRB1 alleles are associated with the susceptibility to sporadic PD in Chinese Han population, among them HLA-DRB1*0301 is a risk allele while the effect of HLA-DRB1*0406 deserves debate.     

Association Studies of Sporadic Parkinson’s Disease in the Genomic Era

Parkinson’s disease is a common age-related progressive neurodegenerative disorder. Over the last 10 years, advances have been made in our understanding of the etiology of the disease with the greatest insights perhaps coming from genetic studies, including genome-wide association approaches. These large scale studies allow the identification of genomic regions harboring common variants associated to disease risk. Since the first genome-wide association study on sporadic Parkinson’s disease performed in 2005, improvements in study design, including the advent of meta-analyses, have allowed the identification of ~21 susceptibility loci. The first loci to be nominated were previously associated to familial PD (SNCA, MAPT, LRRK2) and these have been extensively replicated. For other more recently identified loci (SREBF1, SCARB2, RIT2) independent replication is still warranted. Cumulative risk estimates of associated variants suggest that more loci are still to be discovered. Additional association studies combined with deep re-sequencing of known genome-wide association study loci are necessary to identify the functional variants that drive disease risk. As each of these associated genes and variants are identified they will give insight into the biological pathways involved the etiology of Parkinson’s disease. This will ultimately lead to the identification of molecules that can be used as biomarkers for diagnosis and as targets for the development of better, personalized treatment.     

Calpastatin Gene (CAST) Is Not Associated with Late Onset Sporadic Parkinson’s Disease in the Han Chinese Population

Recent studies point to an association between the late-onset sporadic Parkinson’s disease (PD) and single nucleotide polymorphisms (SNPs) rs1559085 and rs27852 in Ca²⁺-dependent protease calpain inhibitor calpastatin (CAST) gene. This finding is of interest since loss of CAST activity could result in over activated calpain, potentially leading to Ca²⁺ dysregulation and loss of substantia nigra neurons in PD. We explored the association between CAST SNPs and late-onset sporadic PD in the Han Chinese population. The study included 615 evaluable patients (363 male, 252 female) with PD and 636 neurologically healthy controls (380 male, 256 female) matched for age, gender, ethnicity, and area of residence. PD cases were identified from the PD cohort of the Chinese National Consortium on Neurodegenerative Diseases (www.chinapd.cn). A total of 24 tag-SNPs were genotyped capturing 95% of the genetic variation across the CAST gene. There was no association found between any of the polymorphisms and PD in all models tested (co-dominant, dominant-effect and recessive-effect). Similarly, none of the common haplotypes was associated with a risk for PD. Our data do not support a significant association between the CAST gene polymorphisms and late onset sporadic PD in the Han Chinese population.     

Association of Histamine N-Methyltransferase Thr105Ile Polymorphism with Parkinson’s Disease and Schizophrenia in Han Chinese: A Case-Control Study

Parkinson’s disease (PD) and schizophrenia (SCZ) are frequent central nervous disorders that have unclear etiologies but that show similarities in their pathogenesis. Since elevated histamine levels in the brain have been associated with PD and SCZ, we wanted to explore whether the Thr105Ile substitution in the histamine N-methyltransferase gene (HNMT-Thr105Ile), which impairs histamine degradation, is associated with either disease. We used the ligase detection reaction to genotype a case-control cohort of Han Chinese patients with PD or SCZ and healthy controls at the HNMT-Thr105Ile locus. The Ile allele was associated with reduced risk of PD (OR 0.516, 95%CI 0.318 to 0.838, p = 0.007) and of SCZ (OR 0.499, 95%CI 0.288 to 0.865, p = 0.011). Genotype frequencies and minor allele frequencies were similar between patients and controls when we compared males with females or early-onset patients with late-onset ones. Genotype and allele frequencies were not significantly different between PD patients with dyskinesia and PD patients without dyskinesia. Our results suggest that the heterozygous Thr/Ile genotype at the HNMT-Thr105Ile locus and the minor Ile105 allele protect against PD and SCZ in Han Chinese.     

Genetic Heterogeneity of Susceptibility Gene in Different Ethnic Populations: Refining Association Study of PTPN22 for Graves’ Disease in a Chinese Han Population

In our previous studies, we presumed subtypes of Graves’ disease (GD) may be caused by different major susceptibility genes or different variants of a single susceptibility gene. However, more evidence is needed to support this hypothesis. Single-nucleotide polymorphism (SNP) rs2476601 in PTPN22 is the susceptibility loci of GD in the European population. However, this polymorphism has not been found in Asian populations. Here, we investigate whether PTPN22 is the susceptibility gene for GD in Chinese population and further determine the susceptibility variant of PTPN22 in GD. We conducted an imputation analysis based on the results of our genome-wide association study (GWAS) in 1,536 GD patients and 1,516 control subjects. Imputation revealed that 255 common SNPs on a linkage disequilibrium (LD) block containing PTPN22 were associated with GD (P<0.05). Nine tagSNPs that captured the 255 common variants were selected to be further genotyped in a large cohort including 4,368 GD patients and 4,350 matched controls. There was no significant difference between the nine tagSNPs (P>0.05) in either the genotype distribution or allelic frequencies between patients and controls in the replication study. Although the combined analysis exhibited a weak association signal (P _combined = 0.003263 for rs3811021), the false positive report probability (FPRP) analysis indicated it was most likely a false positive finding. Our study did not support an association of common SNPs in PTPN22 LD block with GD in Chinese Han population. This suggests that GD in different ethnic population is probably caused by distinct susceptibility genes.     

Genetic Variations of GAK in Two Chinese Parkinson’s Disease Populations: A Case-Control Study

Cyclin G-associated kinase (GAK) modifies α–synuclein expression levels and affects the susceptibility of Parkinson’s disease (PD). The single-nucleotide polymorphism (SNP) rs1564282 of GAK gene has a significant association to the risk of PD among Caucasian populations. To date there is only one data with regards to ethnic Chinese from Mainland China. Here, we conducted a case-control study in two independent cohorts of Han Chinese populations from Taiwan and Singapore to validate this association. A total of 1,755 subjects (871 PD patients and 884 controls) were recruited. The results showed that neither the CT, TT genotypes nor the minor allele T of SNP rs1564282 were associated with PD among the subjects from Taiwan and Singapore as well as in the pooled analysis. Differences in our study population with regards to published literature may be due to epigenetic factors and gene-gene or gene-environmental interactions. Further studies in other Chinese populations will be of interest to validate these findings.     

Do mtDNA Mutations Participate in the Pathogenesis of Sporadic Parkinson’s Disease?

The pathogenesis of sporadic Parkinson’s disease (PD) remains enigmatic. Mitochondrial complex-I defects are known to occur in the substantia nigra (SN) of PD patients and are also debated in some extracerebral tissues. Early sequencing efforts of the mitochondrial DNA (mtDNA) did not reveal specific mutations, but a long lasting discussion was devoted to the issue of randomly distributed low level point mutations, caused by oxidative stress. However, a potential functional impact remained a matter of speculation, since heteroplasmy (mutational load) at any base position analyzed, remained far below the relevant functional threshold. A clearly age-dependent increase of the ‘common mtDNA deletion’ had been demonstrated in most brain regions by several authors since 1992. However, heteroplasmy did hardly exceed 1% of total mtDNA. It became necessary to exploit PCR techniques, which were able to detect any deletion in a few microdissected dopaminergic neurons of the SN. In 2006, two groups published biochemically relevant loads of somatic mtDNA deletions in these neurons. They seem to accumulate to relevant levels in the SN dopaminergic neurons of aged individuals in general, but faster in those developing PD. It is reasonable to assume that this accumulation causes mitochondrial dysfunction of the SN, although it cannot be taken as a final proof for an early pathogenetic role of this dysfunction. Recent studies demonstrate a distribution of deletion breakpoints, which does not differ between PD, aging and classical mitochondrial disorders, suggesting a common, but yet unknown mechanism.     

Genetic Variation in the REL Gene Increases Risk of Behcet’s Disease in a Chinese Han Population but That of PRKCQ Does Not

Genome-wide association studies (GWAS) and candidate gene studies have identified the REL and PRKCQ genes as risk loci for various autoimmune diseases. The purpose of the present study was to investigate the association of the REL and PRKCQ genes with Behcet’s disease (BD) in a Chinese Han population. A case-control study was conducted on three single nucleotide polymorphisms (SNPs), rs13031237, rs702873, and rs842647 of the REL gene and three SNPs (rs4750316, rs11258747, and rs947474) of the PRKCQ gene using polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) in a total of 623 BD patients and 1,074 healthy controls. Multiple variables were assessed, including age, sex distribution, and extra-ocular findings. In the present study, the frequencies of rs842647 GG genotypes and rs842647 G alleles were significantly higher in patients than in controls and those of the rs842647 AG genotypes were lower in patients than in controls [GG genotype: Bonferroni corrected P-value for gender adjustment (P_c^a) = 0.0074, odds ratio (OR) = 1.63; G allele: P_c^a = 0.0072, OR = 1.57; AG genotype: P_c^a = 0.024, OR = 0.63, respectively]. No statistically significant differences in the frequencies of rs702873, rs13031237, rs4750316, rs11258747, and rs947474 between BD patients and controls were observed. Stratification analysis indicated that the REL rs842647 polymorphism was associated with BD patients with skin lesions. No significant association of the other five SNPs between BD patients with other extra-ocular findings, including genital ulcer, arthritis, and positive pathergy test results was found. The REL rs842647 polymorphism may be a susceptibility factor for BD pathogenesis and skin lesions, which indicate that c-Rel may be involved in the pathogenesis and skin lesions of BD through the NF-κB pathway.     

Parkinson’s Disease in Saudi Patients: A Genetic Study

Parkinson’s disease (PD) is one of the major causes of parkinsonism syndrome. Its characteristic motor symptoms are attributable to dopaminergic neurons loss in the midbrain. Genetic advances have highlighted underlying molecular mechanisms and provided clues to potential therapies. However, most of the studies focusing on the genetic component of PD have been performed on American, European and Asian populations, whereas Arab populations (excluding North African Arabs), particularly Saudis remain to be explored. Here we investigated the genetic causes of PD in Saudis by recruiting 98 PD-cases (sporadic and familial) and screening them for potential pathogenic mutations in PD-established genes; SNCA, PARKIN, PINK1, PARK7/DJ1, LRRK2 and other PD-associated genes using direct sequencing. To our surprise, the screening revealed only three pathogenic point mutations; two in PINK1 and one in PARKIN. In addition to mutational analysis, CNV and cDNA analysis was performed on a subset of patients. Exon/intron dosage alterations in PARKIN were detected and confirmed in 2 cases. Our study suggests that mutations in the ORF of the screened genes are not a common cause of PD in Saudi population; however, these findings by no means exclude the possibility that other genetic events such as gene expression/dosage alteration may be more common nor does it eliminate the possibility of the involvement of novel genes.     

A New Hope for a Devastating Disease: Hydrogen Sulfide in Parkinson’s Disease

Hydrogen sulfide (H₂S) has been regarded as the third gaseous transmitter alongside nitric oxide (NO) and carbon monoxide (CO). In mammalian brain, H₂S is produced redundantly by four enzymatic pathways, implying its abundance in the organ. In physiological conditions, H₂S has been found to induce the formation of long-term potential in neuronal cells by augmenting the activity of N-methyl-D-aspartate (NMDA) receptor. Likewise, it also actively takes part in the regulation of intracellular Ca²⁺ and pH homeostasis in both neuronal cells and glia cells. Intriguingly, emerging evidence indicates a connection of H₂S with Parkinson’s disease. Specifically, the endogenous H₂S level in the substantia nigra (SN) is significantly reduced along with 6-hydroxydopamine (6-OHDA) treatment in rats, while supplementation of H₂S not only reverses 6-OHDA-induced neuronal loss but also attenuates the following disorders of movement, suggesting a protective effect of H₂S in Parkinson’s disease (PD). Remarkably, the protective effect has been extensively demonstrated with various in vitro and in vivo PD models. These suggest that H₂S may be a new hope for the treatment of PD. Further studies have shown that the protective effects can be ascribed to H₂S-mediated anti-oxidation, anti-inflammation, anti-apoptosis, and pro-survival activity, which are also summarized in the review. Moreover, the progresses on the development of H₂S donors are also conveyed with an emphasis on the treatment of PD. Nevertheless, one should bear in mind that the precise role of H₂S in the pathogenesis of PD remains largely elusive. Therefore, more studies are warranted before turning the hope into a real therapy for PD.     

The S-Nitrosylation Status of PCNA Localized in Cytosol Impacts the Apoptotic Pathway in a Parkinson’s Disease Paradigm

It is generally accepted that nitric oxide (NO) or its derivatives, reactive nitrogen species (RNS), are involved in the development of Parkinson’s disease (PD). Recently, emerging evidence in the study of PD has indicated that protein S-nitrosylation triggers the signaling changes in neurons. In this study, SH-SY5Y cells treated with rotenone were used as a model of neuronal death in PD. The treated cells underwent significant apoptosis, which was accompanied by an increase in intracellular NO in a rotenone dose-dependent manner. The CyDye switch approach was employed to screen for changes in S-nitrosylated (SNO) proteins in response to the rotenone treatment. Seven proteins with increased S-nitrosylation were identified in the treated SH-SY5Y cells, which included proliferating cell nuclear antigen (PCNA). Although PCNA is generally located in the nucleus and participates in DNA replication and repair, significant PCNA was identified in the SH-SY5Y cytosol. Using immunoprecipitation and pull-down approaches, PCNA was found to interact with caspase-9; using mass spectrometry, the two cysteine residues PCNA-Cys81 and -Cys162 were identified as candidate S-nitrosylated residues. In addition, the evidence obtained from in vitro and the cell model studies indicated that the S-nitrosylation of PCNA-Cys81 affected the interaction between PCNA and caspase-9. Furthermore, the interaction of PCNA and caspase-9 partially blocked caspase-9 activation, indicating that the S-nitrosylation of cytosolic PCNA may be a mediator of the apoptotic pathway.     

Upregulation of GPR109A in Parkinson’s Disease

Background

Anecdotal animal and human studies have implicated the symptomatic and neuroprotective roles of niacin in Parkinson’s disease (PD). Niacin has a high affinity for GPR109A, an anti-inflammatory receptor. Niacin is also thought to be involved in the regulation of circadian rhythm. Here we evaluated the relationships among the receptor, niacin levels and EEG night-sleep in individuals with PD.

Methods and Findings

GPR109A expression (blood and brain), niacin index (NAD-NADP ratio) and cytokine markers (blood) were analyzed. Measures of night-sleep function (EEG) and perceived sleep quality (questionnaire) were assessed. We observed significant up-regulation of GPR109A expression in the blood as well as in the substantia nigra (SN) in the PD group compared to age-matched controls. Confocal microscopy demonstrated co-localization of GPR109A staining with microglia in PD SN. Pro and anti-inflammatory cytokines did not show significant differences between the groups; however IL1-β, IL-4 and IL-7 showed an upward trend in PD. Time to sleep (sleep latency), EEG REM and sleep efficiency were different between PD and age-matched controls. Niacin levels were lower in PD and were associated with increased frequency of experiencing body pain and decreased duration of deep sleep.

Conclusions

The findings of associations among the GPR109A receptor, niacin levels and night-sleep function in individuals with PD are novel. Further studies are needed to understand the pathophysiological mechanisms of action of niacin, GPR109A expression and their associations with night-sleep function. It would be also crucial to study GPR109A expression in neurons, astrocytes, and microglia in PD. A clinical trial to determine the symptomatic and/or neuroprotective effect of niacin supplementation is warranted.     

Digitomotography in Parkinson’s Disease: A Cross-Sectional and Longitudinal Study

Motor symptoms in Parkinson’s disease (PD) are usually assessed with semi-quantitative tests such as the Unified PD Rating Scale (UPDRS) which are limited by subjectivity, categorical design, and low sensitivity. Particularly bradykinesia as assessed e.g. with speeded index finger tapping exhibits low validity measures. This exploratory study set out to (i) assess whether force transducer-based objective and quantitative analysis of motor coordination in index finger tapping is able to distinguish between PD patients and controls, and (ii) assess longitudinal changes. Sixteen early-stage and 17 mid-stage PD patients as well as 18 controls were included in the cross-sectional part of the study; thirteen, 16 and 16 individuals of the respective groups agreed in a reassessment 12 months later. Frequency, force, rhythmicity, regularity and laterality of speeded and metronome paced tapping were recorded by digitomotography using a quantitative motor system ("Q-Motor"). Analysis of cross-sectional data revealed most consistent differences between PD patients and controls in variability of tap performance across modalities assessed. Among PD patients, variability of taps and the ability to keep a given rhythm were associated with UPDRS motor and finger tapping scores. After 12 months, laterality parameters were reduced but no other parameters changed significantly. This data suggests that digitomotography provides quantitative and objective measures capable to differentiate PD from non-PD in a small cohort, however, the value of the assessment to track PD progression has to be further evaluated in larger cohorts of patients.