Cyrus P. Zabetian

Common genetic variation in the HLA region is associated with late-onset sporadic Parkinson's disease

Parkinsons disease is a common disorder that leads to motor and cognitive disability. We performed a genome-wide association study of 2,000 individuals with Parkinsons disease (cases) and 1,986 unaffected controls from the NeuroGenetics Research Consortium (NGRC). We confirmed associations with SNCA and MAPT, replicated an association with GAK (using data from the NGRC and a previous study, P = 3.2 × 10−9) and detected a new association with the HLA region (using data from the NGRC only, P = 2.9 × 10−8), which replicated in two datasets (meta-analysis P = 1.9 × 10−10). The HLA association was uniform across all genetic and environmental risk strata and was strong in sporadic (P = 5.5 × 10−10) and late-onset (P = 2.4 × 10−8) disease. The association peak we found was at rs3129882, a noncoding variant in HLA-DRA. Two studies have previously suggested that rs3129882 influences expression of HLA-DR and HLA-DQ. The brains of individuals with Parkinsons disease show upregulation of DR antigens and the presence of DR-positive reactive microglia, and nonsteroidal anti-inflammatory drugs reduce Parkinsons disease risk. The genetic association with HLA supports the involvement of the immune system in Parkinsons disease and offers new targets for drug development.

Comprehensive research synopsis and systematic meta-analyses in Parkinson's disease genetics : The PDGene database

More than 800 published genetic association studies have implicated dozens of potential risk loci in Parkinsons disease (PD). To facilitate the interpretation of these findings, we have created a dedicated online resource, PDGene, that comprehensively collects and meta-analyzes all published studies in the field. A systematic literature screen of ∼27,000 articles yielded 828 eligible articles from which relevant data were extracted. In addition, individual-level data from three publicly available genome-wide association studies (GWAS) were obtained and subjected to genotype imputation and analysis. Overall, we performed meta-analyses on more than seven million polymorphisms originating either from GWAS datasets and/or from smaller scale PD association studies. Meta-analyses on 147 SNPs were supplemented by unpublished GWAS data from up to 16,452 PD cases and 48,810 controls. Eleven loci showed genome-wide significant (P<5×10−8) association with disease risk: BST1, CCDC62/HIP1R, DGKQ/GAK, GBA, LRRK2, MAPT, MCCC1/LAMP3, PARK16, SNCA, STK39, and SYT11/RAB25. In addition, we identified novel evidence for genome-wide significant association with a polymorphism in ITGA8 (rs7077361, OR 0.88, Pu200a=u200a1.3×10−8). All meta-analysis results are freely available on a dedicated online database (www.pdgene.org), which is cross-linked with a customized track on the UCSC Genome Browser. Our study provides an exhaustive and up-to-date summary of the status of PD genetics research that can be readily scaled to include the results of future large-scale genetics projects, including next-generation sequencing studies.

Glucocerebrosidase Gene Mutations: A Risk Factor for Lewy Body Disorders

BACKGROUNDnMutations in the glucocerebrosidase (GBA) gene have been reported to modify risk for Parkinson disease (PD) and dementia with Lewy bodies (DLB). However, these findings have not been consistently replicated, and most studies have had substantial methodological shortcomings.nnnOBJECTIVEnTo better assess the role of GBA variants in altering risk for Lewy body disorders.nnnDESIGNnCase-control study.nnnSETTINGnFour movement disorder clinics in the Seattle, Washington, area.nnnPARTICIPANTSnSeven hundred twenty-one patients with PD, 554 healthy control subjects, and 57 patients with DLB.nnnMAIN OUTCOME MEASURESnDisease status and presence or absence of the 2 most common GBA mutations (N370S and L444P).nnnRESULTSnWe observed a significantly higher heterozygote frequency for the 2 mutations in patients with PD (2.9%; P <.001) and those with DLB (3.5%; P = .045) compared with control subjects (0.4%).nnnCONCLUSIONnOur findings suggest that GBA mutations exert a large effect on susceptibility for Lewy body disorders at the individual level but are associated with a modest (approximately 3%) population-attributable risk in individuals of European ancestry.

Combined Effects of Smoking, Coffee, and NSAIDs on Parkinson's Disease Risk

Inverse associations of Parkinsons disease (PD) with cigarette smoking, coffee drinking, and nonsteroidal anti‐inflammatory drug (NSAID) use have been reported individually, but their joint effects have not been examined. To quantify associations with PD for the individual, two‐way and three‐way combinations of these factors, a case–control association study with 1,186 PD patients and 928 controls was conducted. The study setting was the NeuroGenetics Research Consortium. Subjects completed a structured questionnaire regarding smoking, coffee, and NSAID consumption. Odds ratios were calculated using unconditional logistic regression. Smoking, coffee, and over the counter NSAID use as individual factors exhibited significantly reduced risks of 20% to 30%. The two‐way and three‐way combinations were associated with risk reduction of 37% to 49%, and 62%, respectively. Smoking and coffee exhibited significant inverse risk trends with increasing cumulative exposures, suggesting dose–response relations. With respect to the combination of all three exposures, persons who were at the highest exposure strata for smoking and coffee and used NSAIDs had an estimated 87% reduction in risk (OR = 0.13, 95% CI = 0.06–0.29). Whether this finding reflects true biologic protection needs to be investigated.

Phosphorylated α-Synuclein in Parkinson’s Disease

An assay for detecting phosphorylated α-synuclein in CSF may help to diagnose Parkinson’s disease and determine disease severity. Tracking the Course of Neurodegeneration Parkinson’s disease (PD), a neurodegenerative disorder characterized by loss of motor function, affects millions of people worldwide. Although there are drugs that can replace dopamine and thus compensate for the loss of dopaminergic neurons of the nigrostriatal pathway, there is no treatment that can prevent neuronal degeneration. A big goal has been to discover biomarkers that could be used to distinguish PD from other parkinsonian disorders, such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), and to follow disease progression. To date, one of the most extensively tested markers is α-synuclein, a protein that has been implicated in the pathogenesis of PD. There is a decrease in the concentration of α-synuclein in the cerebrospinal fluid (CSF) of patients with PD compared to healthy individuals. However, α-synuclein does not appear to be useful in terms of differentiating PD from other parkinsonian disorders with overlapping symptoms and does not correlate with PD severity or progression. Now, Wang and colleagues have identified an isoform of α-synuclein, phosphorylated α-synuclein (PS-129), in human CSF that may prove to be a more useful marker of PD than α-synuclein. First, the authors developed a highly sensitive and specific assay to measure PS-129 concentrations as well as total α-synuclein in CSF samples from healthy individuals and from a cohort of patients with PD, MSA, PSP, and Alzheimer’s disease. The authors discovered that the PS-129 concentration in CSF, when combined with the total α-synuclein concentration in CSF, helped to distinguish PD patients from those with MSA and PSP. Additionally, CSF PS-129 concentrations in CSF correlated with disease severity in PD patients. These early results suggest that PS-129 may be useful as a marker to assist in the differential diagnosis of PD and to monitor disease progression. This would be of value for selecting patients for clinical trials to test new PD-modifying therapies as they become available and to monitor disease in response to these treatments. However, before PS-129 can be deployed as a marker for PD, it will need to be validated in independent cohorts of PD patients, especially those with samples collected longitudinally. Phosphorylated α-synuclein (PS-129), a protein implicated in the pathogenesis of Parkinson’s disease (PD), was identified by mass spectrometry in human cerebrospinal fluid (CSF). A highly sensitive and specific assay was established and used to measure PS-129 together with total α-synuclein in the CSF of patients with PD, other parkinsonian disorders such as multiple system atrophy (MSA) and progressive supranuclear palsy (PSP), and healthy individuals (a total of ~600 samples). PS-129 CSF concentrations correlated weakly with PD severity and, when combined with total α-synuclein concentrations in CSF, contributed to distinguishing PD from MSA and PSP. Further rigorous validation in independent cohorts of patients, especially those where samples have been collected longitudinally, will determine whether the concentration of PS-129 in CSF will be useful for diagnosing PD and for monitoring PD severity and progression.

Lack of replication of thirteen single-nucleotide polymorphisms implicated in Parkinson’s disease: a large-scale international study

BACKGROUNDnA genome-wide association study identified 13 single-nucleotide polymorphisms (SNPs) significantly associated with Parkinsons disease. Small-scale replication studies were largely non-confirmatory, but a meta-analysis that included data from the original study could not exclude all SNP associations, leaving relevance of several markers uncertain.nnnMETHODSnInvestigators from three Michael J Fox Foundation for Parkinsons Research-funded genetics consortia-comprising 14 teams-contributed DNA samples from 5526 patients with Parkinsons disease and 6682 controls, which were genotyped for the 13 SNPs. Most (88%) participants were of white, non-Hispanic descent. We assessed log-additive genetic effects using fixed and random effects models stratified by team and ethnic origin, and tested for heterogeneity across strata. A meta-analysis was undertaken that incorporated data from the original genome-wide study as well as subsequent replication studies.nnnFINDINGSnIn fixed and random-effects models no associations with any of the 13 SNPs were identified (odds ratios 0.89 to 1.09). Heterogeneity between studies and between ethnic groups was low for all SNPs. Subgroup analyses by age at study entry, ethnic origin, sex, and family history did not show any consistent associations. In our meta-analysis, no SNP showed significant association (summary odds ratios 0.95 to 1.08); there was little heterogeneity except for SNP rs7520966.nnnINTERPRETATIONnOur results do not lend support to the finding that the 13 SNPs reported in the original genome-wide association study are genetic susceptibility factors for Parkinsons disease.

Exploring gene-environment interactions in Parkinson’s disease

The objective of this study was to explore combined effects of four candidate susceptibility genes and two exposures on Parkinson’s disease (PD) risk; namely, α-synuclein (SNCA) promoter polymorphism REP1, microtubule-associated protein tau (MAPT) H1/H2 haplotypes, apolipoprotein E (APOE) ε2/ε3/ε4 polymorphism, ubiquitin carboxy-terminal esterase L1 (UCHL1) S18Y variant, cigarette smoking and caffeinated coffee consumption. 932 PD patients and 664 control subjects from the NeuroGenetics Research Consortium, with complete data on all six factors, were studied. Uniform protocols were used for diagnosis, recruitment, data collection and genotyping. A logistic regression model which included gene-exposure interactions was applied. Likelihood ratio tests (LRTs) were used for significance testing and Bayesian inference was used to estimate odds ratios (ORs). MAPT (Pxa0=xa00.007), SNCA REP1 (Pxa0=xa00.012), smoking (Pxa0=xa00.001), and coffee (Pxa0=xa00.011) were associated with PD risk. Two novel interactions were detected: APOE with coffee (Pxa0=xa00.005), and REP1 with smoking (Pxa0=xa00.021). While the individual main effects were modest, each yielding ORxa0<xa01.6, the effects were cumulative, with some combinations reaching ORxa0=xa012.6 (95% CI: 5.9–26.8). This study provides evidence for the long-held notion that PD risk is modulated by cumulative and interactive effects of genes and exposures. Furthermore, the study demonstrates that while interaction studies are useful for exploring risk relationships that might otherwise go undetected, results should be interpreted with caution because of the inherent loss of power due to multiple testing. The novel findings of this study that warrant replication are the evidence for interaction of coffee with APOE, and of smoking with REP1 on PD risk.

A comprehensive analysis of deletions, multiplications, and copy number variations in PARK2

Objectives: To perform a comprehensive population genetic study of PARK2. PARK2 mutations are associated with juvenile parkinsonism, Alzheimer disease, cancer, leprosy, and diabetes mellitus, yet ironically, there has been no comprehensive study of PARK2 in control subjects; and to resolve controversial association of PARK2 heterozygous mutations with Parkinson disease (PD) in a well-powered study. Methods: We studied 1,686 control subjects (mean age 66.1 ± 13.1 years) and 2,091 patients with PD (mean onset age 58.3 ± 12.1 years). We tested for PARK2 deletions/multiplications/copy number variations (CNV) using semiquantitative PCR and multiplex ligation-dependent probe amplification, and validated the mutations by real-time quantitative PCR. Subjects were tested for point mutations previously. Association with PD was tested as PARK2 main effect, and in combination with known PD risk factors: SNCA, MAPT, APOE, smoking, and coffee intake. Results: A total of 0.95% of control subjects and 0.86% of patients carried a heterozygous CNV mutation. CNV mutations found in 16 control subjects were all in exons 1–4, sparing exons that encode functionally critical protein domains. Thirteen patients had 2 CNV mutations, 5 had 1 CNV and 1 point mutation, and 18 had 1 CNV mutation. Mutations found in patients spanned exons 2–9. In whites, having 1 CNV was not associated with increased risk (odds ratio 1.05, p = 0.89) or earlier onset of PD (64.7 ± 8.6 heterozygous vs 58.5 ± 11.8 normal). Conclusions: This comprehensive population genetic study in control subjects fills the void for a PARK2 reference dataset. There is no compelling evidence for association of heterozygous PARK2 mutations, by themselves or in combination with known risk factors, with PD.

Genetic association between α-synuclein and idiopathic parkinson's disease†

Point mutations and copy number variations in SNCA, the gene encoding α‐synuclein, cause familial Parkinsons disease (PD). A dinucleotide polymorphism (REP1) in the SNCA promoter may be a risk factor for common forms of PD. We studied 1,802 PD patients and 2,129 controls from the NeuroGenetics Research Consortium, using uniform, standardized protocols for diagnosis, subject recruitment, data collection, genotyping, and data analysis. Three common REP1 alleles (257, 259, and 261 bp, with control frequencies of 0.28, 0.65, and 0.06) and several rare alleles (combined frequency <0.01) were detected. We confirmed association of REP1 with PD risk [odds ratio (OR)u2009=u20090.86, Pu2009=u20090.006 for 257‐carriers; ORu2009=u20091.25, Pu2009=u20090.022 for 261‐carriers]. Using a normalization procedure, we showed that the 257 and 261 alleles are both independently associated with PD risk (for 257, Pu2009=u20090.002 in overall data, 0.003 in non‐familial PD, 0.001 in early‐onset PD; for 261, Pu2009=u20090.056 in overall data, 0.024 in non‐familial PD, 0.052 in early‐onset PD). The 257‐associated risk was consistent with a dominant model [hazard ratio (HR)u2009=u20090.99, Pu2009=u20090.91 for 257/257 vs. 257/X where X denotes all other common alleles; HRu2009=u20091.16, Pu2009=u20090.004 for X/X vs. 257/X]. The 261‐associated risk was consistent with a recessive model (HRu2009=u20091.89, Pu2009=u20090.026 for 261/261 vs. 261/X; HRu2009=u20090.95, Pu2009=u20090.42 for X/X vs. 261/X). Genotype‐specific mean onset ages (±SD) ranged from 54.8u2009±u200912.1 for 261/261 to 59.4u2009±u200911.5 for 257/257, displaying a trend of decreasing onset age with increasing allele size (Pu2009=u20090.055). Genetic variation in SNCA and its regulatory regions play an important role in both familial and sporadic PD.

Disease-related and genetic correlates of psychotic symptoms in Parkinson's disease.

Our aim was to examine disease‐related and genetic correlates of the development of psychotic symptoms in a large population of patients with Parkinsons disease. We studied 500 patients with Parkinsons disease from the NeuroGenetics Research Consortium using logistic regression models. Predictors were demographic, clinical (motor/nonmotor features), and genetic, measured as continuous or dichotomous variables. Continuous measures were divided into population‐based tertiles. Results are given as odds ratios (95% confidence intervals) for dichotomous variables and by ascending tertile for continuous variables. Psychotic symptoms were associated with increasing age: 4.86 (1.62–14.30) and 6.25 (2.09–18.74) (test for trend: P = 0.01); and duration of disease: 3.81 (1.23–11.76) and 5.33 (1.68–16.89) (test for trend: P = 0.03). For nonmotor features, we demonstrated positive trends with depression: 1.31 (0.47–3.61) and 5.01 (2.04–12.33) (test for trend: P < 0.0001); cognitive dysfunction: 0.69 (0.26–1.84) and 2.51 (1.00–6.29) (test for trend: P = 0.03); and an excess for those with sleep disorders: 2.00 (1.03–3.89) (P = 0.04). Psychotic symptoms were not associated with tremor or postural instability scores, but there was an association with freezing of gait: 3.83 (1.67–8.75) (P < 0.002). Psychotic symptoms were not associated with the presence of any examined polymorphisms in the apolipoprotein, alpha‐synuclein, or microtubule associated protein tau genes. This is the largest study to examine correlates of psychotic symptoms in Parkinsons disease. We discovered a novel association with freezing of gait. We demonstrated an association with depression and duration of disease, both of which were inconsistently related in previous studies, and confirmed the association with age, cognitive dysfunction, and sleep disorders.