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Leucine-rich repeat kinase 2 (LRRK2) is known to harbor highly penetrant mutations linked to familial parkinsonism. However, its full polymorphic variability in relationship to Parkinson’s disease (PD) risk has not been systematically assessed.
We examined the frequency pathogenicity of 121 exonic LRRK2 variants in three ethnic series (Caucasian [N=12,590], Asian [N=2,338] and Arab-Berber [N=612]) consisting of 8,611 patients and 6,929 control subjects from 23 separate sites of the Genetic Epidemiology of Parkinson’s Disease Consortium.
Excluding carriers of previously known pathogenic mutations, new independent risk associations were found for polymorphic variants in Caucasian (p.M1646T, OR: 1.43, 95% CI: 1.15 – 1.78, P=0.0012) and Asian (p.A419V, OR: 2.27, 95% CI: 1.35 – 3.83, P=0.0011) populations. In addition, a protective haplotype was observed at >5% frequency (p.N551K-p.R1398H-p.K1423K) in the Caucasian and Asian series’, with a similar finding in the small Arab-Berber series that requires further study (combined 3-series OR: 0.82, 95% CI: 0.72 – 0.94, P=0.0043). Of the two previously reported Asian risk variants p.G2385R was found to be associated with disease (OR: 1.73, 95% CI: 1.20 – 2.49, P=0.0026) but no association was observed for p.R1628P (OR: 0.62, 95% CI: 0.36 – 1.07, P=0.087). Also in the Arab-Berber series, p.Y2189C showed potential evidence of risk association with PD (OR: 4.48, 95% CI: 1.33 – 15.09, P=0.012). Of note, two variants (p.I1371V and p.T2356I) which have been previously proposed as pathogenic were observed in patient and control subjects at the same frequency.
LRRK2 offers an example where multiple rare and common genetic variants in the same gene have independent effects on disease risk. Lrrk2, and the pathway in which it functions, is important in the etiology and pathogenesis of a greater proportion of patients with PD than previously believed.
The present study and original funding for the GEO-PD Consortium was supported by grants from Michael J. Fox Foundation. Studies at individual sites were supported by a number of funding agencies world-wide.
Parkinson’s disease (PD) is generally considered a late-onset sporadic disorder. Nevertheless, genetic insights have helped to define the molecular etiology and have provided new models to develop neuroprotective interventions. Mutations of the leucine-rich repeat kinase 2 gene (LRRK2; Lrrk2) are now recognized as the most frequent genetic determinant of familial and sporadic PD1. The LRRK2 gene (51 exons) encodes a protein (2527 amino acid; Lrrk2) which has five conserved domains: including a Roc (Ras in complex proteins; Rab GTPase) and a catalytic core common to both tyrosine and serine/threonine kinases.
Pathogenic LRRK2 variability has been identified by sequencing of probands with familial parkinsonism, with results confirmed and occasionally extended within community and/or clinically-based patient-control series2–6. Seven definite pathogenic mutations (Lrrk2 p.N1437H, p.R1441C/G/H, p.Y1699C, p.G2019S, and p.I2020T) have been described7, 8. These mutations may be relatively frequent in patients from specific ethnicities, although still rare in ethnically-matched control subjects. Lrrk2 p.R1441G is found in more than 8% of patients originating in the Basque region of Northern Spain 9, whereas Lrrk2 p.G2019S is found in 30% of Arab-Berber patients with PD10, 11. LRRK2 polymorphisms (>1% minor allele frequency) have also been associated with PD in Asia, for which the estimated attributable risk is often dependent on the specific ethnicity. Lrrk2 p.R1628P and p.G2385R are each found in 3–4% of individuals of Chinese descent and increase the risk of PD by approximately two-fold12–15.
However, the large majority of LRRK2 variants have not been systematically studied. It is possible that LRRK2 may harbor many more variants that are important for determining PD pathogenicity and clinical risk. To address this possibility, with the Genetic Epidemiology of Parkinson’s Disease (GEO-PD) consortium we have examined frequency of 121 LRRK2 exonic variants in 15,540 subjects including 8,611 patients with PD, and assessed their role in disease susceptibility.
The GEO-PD consortium includes investigators from 35 sites representing 22 countries, and six continents. All GEO-PD sites were invited to participate in this study. A total of 23 sites representing 15 countries and 5 continents agreed to participate in the current study and contributed clinical data for a total of 15,540 individuals (8,611 patients with PD and 6,929 controls). The Caucasian series consisted of 6,995 PD cases and 5,595 controls, the Asian series consisted of 1,376 PD cases and 962 controls, and the Arab-Berber series consisted of 240 PD cases and 372 controls. Patients were diagnosed using either the Gelb or the United Kingdom Parkinson’s Disease Brain Bank (the exclusion criterion “>1 affected relative” was not included). Controls were collected at each site as unrelated healthy individuals (not all controls would have been given a detailed neurological examination but would have been asked about prior diagnosis of a neurological disorder or family history). Demographics for each series are shown in Table 1 and the sample size breakdown from each site is provided in Supplemental Table 1. All human biological samples were collected, fulfilling requested ethical approvals, and used in accord with the terms of subjects’ informed consent.
LRRK2 exonic variants were identified through searches of available literature up to April 1st 2010, personal communications of Consortium members and from unpublished data (Table 2). Genotyping was performed on a Sequenom MassArray iPLEX platform (San Diego, CA) at the Mayo Clinic Florida laboratory of Neurogenetics (except for the groups from Paris, France, and Belgium who supplied genotype data and positive control genomic DNA2, 3); all primer sequences are provided in Supplemental Table 2. In total 8 iPLEX variant combinations were used to incorporate 123 LRRK2 coding variants (Table 2). Positive control DNA was included for each variant; where positive genomic control DNA was unavailable a synthetic positive control DNA sequence was generated by a mismatch primer PCR method. A chi-square test followed by Bonferroni correction was used to test for deviation from Hardy Weinberg equilibrium (HWE) in controls for each site. Direct DNA sequencing was employed to confirm genotyping for all variants with a frequency below 0.3% (n<50).
All analyses were performed separately for the Caucasian, Asian and Arab-Berber series’. For common variants with a minor allele frequency (MAF) of 0.5% or greater, single variant associations with PD were evaluated utilizing fixed effects logistic regression models, where genotypes were dichotomized as presence versus absence of the minor allele (dominant model) due to the fact that LRRK2 mutations cause an autosomal dominantly inherited form of PD and also given the lack of rare homozygotes for many of the variants; additive models were also examined. Models were adjusted for site in the Asian and Caucasian series’. Sensitivity of results to the use of random effects models was also examined16. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated. Between-site heterogeneity was assessed using likelihood ratio tests for variant by site interaction in logistic regression analysis, and also by estimating the I2 statistic, which is a measure of the proportion of total variation of ORs across sites due to heterogeneity beyond chance17.
For variants with a MAF below 0.5% (rare variants), though we estimated the proportion of carriers separately in patients and controls, no statistical tests were used to evaluate associations with PD due to insufficient power. Instead, we collapsed information across rare variants, acknowledging that this has the potential limitation of mixing groups of variants with protective and risk effects, and evaluated the association between presence of any rare variant and PD in logistic regression analysis adjusted by site18. In exploratory analysis when collapsing across variants, we also employed SIFT prediction freeware to examine only those substitutions predicted as not tolerated.
Haplotype analysis was performed using score tests for association with adjustment made for site19; haplotypes of frequency <0.5% were not considered. Any patient with a copy of the minor allele for any of the pathogenic variants that were observed in the study population (p.R1441C, p.R1441H, or p.G2019S) was excluded from all disease-association analysis in order to prevent confounding by these pathogenic variants; these patients were not excluded for any other portion of the analysis. Linkage disequilibrium (LD) between variants was assessed using r2 values in study controls, separately for each series. Single variant associations with age at onset were examined using linear regression models, adjusting for site in the Caucasian and Asian series’; regression coefficients and 95% CIs were estimated.
We adjusted for multiple testing using the single-step minP method20, with 10,000 within-site permutations of outcome labels in order to determine the level of significance that controls the family-wise error rate at 5%. After this adjustment, P≤0.0033 was considered significant in the Caucasian and P≤0.0038 in the Asian logistic regression disease-association analysis, while P≤0.0035 was considered significant in the Caucasian and P≤0.0037 was considered significant in the Asian linear regression age at onset association analysis. Note that adjusted significance cutoff levels differ between the Caucasian and Asian series due to the different number of tests performed in each, and the different correlation structures between variants within them. For the relatively small Arab-Berber series no adjustment for multiple testing was made, and as such these results are considered of a more exploratory nature. All statistical analyses were performed using the SAS software package (version 9.2; SAS Institute; Cary, North Carolina) or S-Plus (version 8.0.1; Insightful Corporation, Seattle, Washington).
A total of 123 LRRK2 variants were selected for genotype analysis; however two variants (p.R793M and p.L2466H) failed to assay by iPLEX and were subsequently dropped from the study. All other variants (n=121) were genotyped through the entire patient-control series (n=15,540). All genotype call rates for the series’ were >95%. Deviation from HWE among controls for each site (all P>0.05), was observed for p.N2081D in the Norwegian series, which was caused by two patients with a rare homozygote genotype and thus were retained in the analysis. However, Lrrk2 p.N289N and p.P1262A were dropped from the Arab-Berber analysis due to significant variation from HWE due to an increased number of rare minor allele homozygotes which may be due to the consanguineous nature of the population.
Of the 121 LRRK2 exonic variants assessed, 4 were nonsense, 89 missense and 28 silent. In total, 48 variants (including 4 of the 7 known pathogenic mutations) were not observed in the sample of 15,540 patients and controls, suggesting these are rare mutations in the populations originally examined. For the majority of variants the pair-wise LD was weak (r2<0.3), with higher values observed with D′ given the relatively low minor allele frequency for many of these variants (Supplemental Tables 3a–f).
The results of single variant disease-association analysis are displayed in Table 3, separately for the Caucasian, Asian, and Arab-Berber series. In the Caucasian series, significant associations with PD were identified for Lrrk2 p.K1423K (OR: 0.83, 95% CI: 0.74 – 0.92, P=0.0006) and p.M1646T (OR: 1.43, 95% CI: 1.15 – 1.78, P=0.0012). Country-specific ORs and 95% CIs for the risk factor p.M1646T are displayed in Figure 1a. As shown in Supplemental Table 4, between-site heterogeneity in effects was low for p.M1646T (I2=0%, P=0.44) and moderate for p.K1423K (I2=34%, P=0.069).
In the Asian series, significant associations with PD were observed for Lrrk2 p.A419V (OR: 2.27, 95% CI: 1.35 – 3.83, P=0.0011), p.N551K (OR: 0.73, 95% CI: 0.60 – 0.89, P=0.0017), p.R1398H (OR: 0.73, 95% CI: 0.59 – 0.89, P=0.0020), and p.G2385R (OR: 1.73, 95% CI: 1.20 – 2.49, P=0.0026). Country-specific ORs and 95% CIs for these variants are displayed in Figure 1b and 1c; between-site heterogeneity was very low for each aforementioned association in the Asian series (all I2=0%, all P≥0.42, Supplementary Table 4). Of note, Lrrk2 p.R1628P was not associated with PD in the Asian series, with a non-significant protective effect observed (OR: 0.62, 95% CI: 0.36 – 1.07, P=0.087). Upon further examination of this unexpected finding, the protective effect was driven by the Taiwanese series where it was most common (MAF: 3.8%, OR: 0.56, 95% CI: 0.32 – 1.01, P=0.054). Albeit not approaching significance, the risk effect for p.R1628P was observed in the South Korean series (MAF: 0.2%, OR: 1.33, 95% CI: 0.24 – 7.32, P=0.74), at the Seoul site in particular (MAF: 0.2%, OR: 2.47, 95% CI: 0.28 – 22.15, P=0.42). Lrrk2 p.R1628P was not observed in the Japanese series. Also of note, the previously suggested association of p.S1647T with PD in Asian populations14 was not supported in our study (OR:0.97, 95% CI: 0.82 – 1.15, P=0.73).
In a more exploratory analysis for the smaller Arab-Berber series, significant associations (P≤0.05, without correction for multiple testing) with PD were observed for p.K1423K (OR: 0.42, 95% CI: 0.21 – 0.86, P=0.011) and p.Y2189C (OR: 4.48, 95% CI: 1.33 – 15.09, P=0.012). Larger Arab-Berber series’ are needed to confirm these associations.
Results seen in single variant disease-association analysis in each series remained similar when adjusting for age and gender for the subjects (94.9%) for whom this information was available (Supplemental Table 5) and under an additive model (Supplemental Table 6). Effect sizes were also similar when adjusting simultaneously for other variants significantly associated with PD in a given series, and also when adjusting for p.R1628P in the Asian series where previous association has been demonstrated (Supplemental Table 7), providing evidence that these associations are independent of one another. When utilizing a random effects model for the Caucasian and Asian series’, results were generally similar though slightly weaker (Supplementary Table 4) to those of a fixed effects model. Haplotype analysis across the series showed a significant overall association with disease in the Caucasian (P=0.0016) and Asian (P=2 × 10−24) series’, with a trend in the Arab-Berber series (P=0.056). Haplotype associations appear to be driven by variants independently implicated in disease (Supplemental Tables 8a, b and c).
It is worth highlighting associations of Lrrk2 p.N551K, p. R1398H and p.K1423K noted across series (Figure 1c). Lrrk2 p.N551K, p. R1398H and p.K1423K are in strong LD and constitute a common (>5% frequency) protective haplotype that is inversely associated with risk.
Results of all common single variant associations with age at onset are shown in Supplemental Table 9. We did not identify any associations that withstood a multiple testing correction in the Caucasian and Asian series’. In the small Arab-Berber series, p.L153L was associated with an approximately 4-year earlier age at onset (P=0.038), which requires confirmation in larger samples.
A descriptive summary of rare variants (MAF <0.5%) is provided in Table 4 where the proportion of carriers is presented separately for cases and controls in each series. The pathogenic variants p.R1441H was observed in one Asian patient, p.R1441C was observed only in the Caucasian series (10 patients) and p.G2019S was observed in all three series. The ages of the eight p.G2019S control carriers of these pathogenic variants ranged from 48 to 76 years (Median: 64 years). As previously stated, due to the strong confounding potential of these three variants on disease-association analyses, any patient with a copy of these risk alleles was excluded in such analysis, including the summaries presented in Table 4. A number of other possible rare risk variants (p.E334K, p.R1325Q and p.T1410M) and protective variants (p.A221V, p.A1151T and p.D1375E) with notable differences in frequency between patients with PD and controls were observed. Of note, when collapsing across rare variants, the presence of any rare variant was not associated with PD in the Caucasian series (OR: 1.01, 95% CI: 0.81 – 1.25, P=0.95), Asian series (OR: 1.03, 95% CI: 0.57 – 1.85, P=0.92), or Arab-Berber series (OR: 0.78, 95% CI: 0.28 – 2.20, P=0.64). Additionally, no association was observed when collapsing across only those variants predicted as not tolerated using the SIFT prediction program21 (Caucasian series [OR: 0.89, 95% CI: 0.55 – 1.43, P=0.62], Asian series [OR: 1.05, 95% CI: 0.37 – 2.99, P=0.93], or Arab-Berber series [PD cases: 0.0%, Controls: 0.6%, Fisher’s exact P=1.00]). A summary of variants where no carriers were observed in any of the three series’ is provided in Supplemental Table 10 and a complete list of genotype and allele frequencies per site are provided in Supplementary Table 11.
Our study, one of the largest to date in the study of the genetics of PD, shows that a single gene, LRRK2, harbors a large number of both rare and common variants that confer susceptibility to PD in diverse populations. Although population stratification is an inherent caveat of these types of large-scale collaborative efforts (and a potential limitation of the present study in the absence of genome-wide population control markers), these findings exemplify the confluence and independent effects of rare and common variation on gene loci that have a major influence in shaping both familial and sporadic disease.
Of the 121 variants that we assessed approximately one third (n=48) were not observed in any study participant. This includes 4 previously documented pathogenic mutations (Lrrk2 p.N1437H, p.R1441G, p.Y1699C and p.I2020T) illustrating their rarity in the population samples assessed. Twenty-six variants were at a greater than 0.5% frequency in any one of the three different series’, and only thirteen were observed at >0.5% frequency in all three. This highlights the importance of studying genetic variability in large samples separately in different ethnic groups, since both frequencies and genetic effects may vary substantially22.
The newly identified associations warrant further discussion. Lrrk2 p.M1646T in the COR domain was identified in the Caucasian series (OR 1.43) and the effect was consistent across many diverse countries (Figure 1a). This variant was not observed in Asian descent participants and was rare in the Arab-Berber series. Conversely, Lrrk2 p.A419V (OR 2.27) was consistently more common in patients than controls in Asian sites (Figure 1b). Although we cannot exclude the possibility of a non-coding element in LD, the N-terminal region of the protein appears functionally relevant to disease development. Lrrk2 p.M1646T is the first disease-associated common variant to have been identified in Caucasian populations, whereas the p.A419V is now the third risk-factor that appears specific to individuals of Asian ancestry along with p.R1628P and p.G2385R12, 14, 15. Interestingly, in the present study Lrrk2 p.R1628P was not significantly associated with risk in our Asian series. This variant was only common within the Taiwanese series, where a non-significant protective effect was observed. Our lack of replication of the previously reported risk effect for R1628P is likely due to a combination of the low frequency of this variant, the small sample size of the Taiwanese series, natural sampling variation and population heterogeneity, given the results of previous larger studies of ethnic Han Chinese populations (of note Lrrk2 p.G2385R did display association)14, 15,
The identification of a common three variant haplotype (p.N551K-p.R1398H-p.K1423K) across series that appears to act in a protective manner is also important. It suggests the reduced penetrance associated with LRRK2-parkinsonism may be due to variants acting in cis- or trans- with the pathogenic variant and that activity can be exploited to modify symptomatic onset in patients (Figure 1c), and that therapeutic strategies that lower risk in Lrrk2 parkinsonism may protect against symptomatic onset in idiopathic PD14, 23. The previous report of a protective effect for p.N551K and p.R1398H demonstrated a reduced kinase activity for the p.R1398H variant suggesting this ROC domain substitution may be the most likely functional allele on the haplotype14.
Although our study identifies association with common variation only, it also highlights the wealth of rare variants in the LRRK2 gene which may contribute to disease risk. It is increasingly appreciated that genetic loci that contribute to disease risk may do this through variants that span the whole range of MAF, from rare mutations to very frequent SNP alleles24. Despite the very large sample size, we documented only 3 of the 7 previously described pathogenic LRRK2 mutations. Hence, the search for mutations underlying familial PD should include an analysis of single pedigrees, with evaluation in very large population studies. Single pedigrees may yield some false-positives and these can be filtered out with large population samples. For example, two variants (p.I1371V and p.T2356I) have been previously proposed as pathogenic and used to attribute clinical and functional features to LRRK2-parkinsonism25, 26. However, in the present study both variants were observed in patient and control subjects at the same frequency (Table 4). Conversely, we observed a number of other possible rare risk (p.E334K, p.R1325Q and p.T1410M) and protective (p.A211V, p.A1151T and p.D1375E) variants, however given their low frequency even larger meta-analytical approaches are necessary to fully define their role.
This study focused on exonic variants as to date all pathogenic variants identified in LRRK2 have been single nucleotide missense changes. However, silent, synonymous variants were also included as they can result in alternative splicing, and may influence the rate of protein domain folding and secondary modifications (protein translation is a function of codon usage and t-RNA abundance)27. Neither copy number variants nor other risk factors in non-coding regions that regulate LRRK2 expression or alter splicing were examined in the present work.
As genome-wide association and whole genome sequencing studies continue to yield new loci for susceptibility to diverse diseases, our study suggests that it is important to revisit loci where rare or common variants have been identified, since they may harbor a trove of many more independent signals of genetic risk in different populations28–30. Furthermore, LRRK2 sequencing studies in under-represented populations (e.g. South American continent, sub-Saharan Africa, Middle East and Western Asia) will undoubtedly reveal novel ethnic-specific risk variants and may clarify the role of the rare/absent variants in the present study. LRRK2 variants were recently reported as part of the 1000 genome project including novel exonic variants supporting this hypothesis31.
Massively-parallel resequencing (targeted genomic capture of the specific regions e.g. LRRK2, exome, transcriptome and whole-genome sequencing) will identify many more variants in candidate genes that may predispose to disease. Characterization of each will require this type of collaborative international effort to define pathogenicity, the frequency of variants in different populations and their contribution to disease pathogenesis through genotype-phenotype assessment.
We searched PubMed for the terms “LRRK2” and “Genetics Parkinson’s disease” and identified all LRRK2 coding variations published up until April 2010. In addition we also contacted our global network of collaborators and the members of the Genetic epidemiology of Parkinson’s disease consortium (GE-OPD) for unpublished variants.
The study focuses on the role of LRRK2 variation in Parkinson’s disease and has identified a common risk-factor in Caucasian population (p.M1646T), the third common risk factor in Asian populations (p.A419V) and a common global protective haplotype (p.N551K-p.R1398H-p.K1423K). This work complements the recent meta-analysis of PD GWAS, which suggests a possible association at the LRRK2 locus. We define some of the actual genetic variation likely to be driving association observed in recent GWAS efforts and nominate potential functionally- and clinically-relevant variants. We show modulation of the underlying toxic effect is possible given the protective nature of the p.N551K-p.R1398H-p.K1423K haplotype. Perhaps most importantly, the study demonstrates a greater role for LRRK2 in typical, idiopathic PD than previously believed.
The work in the present study was supported by a grant from The Michael J. Fox Foundation for Parkinson’s Research (OAR, MJF). Original funding for the GEO-PD was supported by a grant from The Michael J. Fox Foundation for Parkinson’s Research Edmond J. Safra Global Genetics Consortia program. The Mayo Clinic Jacksonville is a Morris K. Udall Center of Excellence in Parkinson’s Disease Research and was supported by a the gift from the family of Carl Edward Bolch, Jr., and Susan Bass Bolch (DWD, RJU, ZKW, OAR). This research was undertaken, in part, thanks to funding from the Canada Excellence Research Chairs program (MJF; CVG). Leading Edge Endowment Funds, provided by the Province of British Columbia, LifeLabs, and Genome BC, support the Dr. Donald Rix BC Leadership Chair (MJF). Studies at individual sites was supported by a number of different funding agencies world-wide including; Italian Ministry of Health (Ricerca Corrente 2010, Ricerca Finalizzata 2006), Fondazione Livio Patrizi, the Swedish Parkinson Academy, The Swedish Parkinson Foundation, Lund University Research Fund, AFA Insurance and The Royal Physiographic Society in Lund (AP, CN). Federal Ministry for Education and Research [BMBF, NGFNplus; 01GS08134] (RK), the NGFNplus (Neuron-Parkinson-subproject 7) (SG), the South African Medical Research Council and the University of Stellenbosch, South Africa (SB, JC), CHRU de Lille, Univ Lille 2, Inserm, French Ministry PHRCs (1994/, 2002/1918, 2005/1914), Association France Parkinson (2005), Fondation de France 2004-013306, Fondation de la Recherche Médicale (2006), PPF (synucléothèque 2005–2009), the 2 Centres de Ressources Biologiques (IPL-Lille, CHRU-Lille) and its scientific committee (AD, MCCH, Philippe Amouyel, Florence Pasquier, Régis Bordet), the Agence Nationale de la Recherche (ANR-05-NEUR-019 and ANR-08-MNP-012) (AB, SL), grant ES10758 from the National Institutes of Health, the Swedish Research Council, the Swedish Society for Medical Research, the Swedish Society of Medicine, funds from the Karolinska Institutet, and the Parkinson Foundation in Sweden (KW), the Special Research Fund of the University of Antwerp, Research Foundation Flanders (FWO), the Agency for Innovation by Science and Technology in Flanders (IWT), the Interuniversity Attraction Poles (IAP) Program P6/43 of the Belgian Federal Science Policy Office, a Methusalem Excellence Grant of the Flanders Government and the Medical Research Foundation Antwerp and Neurosearch, Antwerp, Belgium. DC is a holder of an FWO PhD fellowship and J.T. receives a FWO postdoctoral fellowship, the NIH/NINDS 1RC2NS070276, NS057567, P50NS072187, Mayo Clinic Florida (MCF) Research Committee CR programs (MCF) (ZKW), the Geriatric Medical Foundation of Queensland for their support (GDM), a career development award from the Volkswagen Foundation and from the Hermann and Lilly Schilling Foundation (CK), the Research Committee of University of Thessaly (Code: 2845), and Institute of Biomedical Research & Technology, CERETETH (Code: 01-04-207) (GH, ED) and GSK team for past sponsorship of research on familial parkinsonism in Tunisia (RG, FH).
In addition a number of people must be acknowledged for their contributions to make this work possible; Ferdinanda Annesi, PhD; Patrizia Tarantino, PhD (Institute of Neurological Sciences, National Research Council); Chiara Riva, PhD (Department of Neuroscience and Biomedical Technologies, University of Milano-Bicocca, Monza, Italy); Roberto Piolti, MD (Department of Neurology, Ospedale San Gerardo, Monza, Italy); Magdalena Boczarska-Jedynak, MD, PhD (Department of Neurology, Medical University of Silesia, Katowice, Poland); Aurélie Duflot, (UMR837 Inserm-Univ Lille 2, CHRU de Lille), Jean-Philippe Legendre, Nawal Waucquier (Neurologie et Pathologie du Mouvement, Clinique de Neurologie du CHU de Lille). Anna Rita Bentivoglio, MD, PhD, Tamara Ialongo, MD, PhD, Arianna Guidubaldi, MD, Carla Piano, MD (Institute of Neurology, Catholic University, Rome, Italy); Karen Nuytemans PhD; David Crosiers MD (Neurodegenerative Brain Diseases Group, Department of Molecular Genetics, VIB; Laboratory of Neurogenetics, Institute Born-Bunge and University of Antwerp); Sebastiaan Engelborghs MD PhD; Peter De Deyn MD PhD (Department of Neurology, ZNA Middelheim and Laboratory of Neurochemistry and Behavior, Institute Born-Bunge and University of Antwerp); David Crosiers MD; Patrick Cras MD PhD (Department of Neurology, University Hospital Antwerp and Laboratory of Neurobiology, Institute Born-Bunge and University of Antwerp); Phil Hyu Lee MD, PhD (Department of Neurology, Yonsei University College of Medicine, Seoul, Korea); Susanne Lindskov, MSc, (Department of Geriatrics and Neurology, Central Hospital Kristianstad, Northeast Skåne Health Care District, Kristianstad, Sweden); Karin Nilsson, PhD (Department of Clinical Science, Section of Geriatric Psychiatry, Lund University, Sweden); Jan Reimer (Department of Neurology, Skåne University Hospital, Sweden); Manabu Funayama, PhD, Yuanzhe Li, MD, PhD (Juntendo University School of Medicine, Tokyo, Japan). From the Queensland Parkinson’s Project: R.S. Boyle and A. Sellbach (Princess Alexandra Hospital, Brisbane), J. D. O’Sullivan (Royal Brisbane and Women’s Hospital, Brisbane), G.T. Sutherland, G.A. Siebert and N.N.W. Dissanayaka (Eskitis Institute for Cell and Molecular Therapies, Griffith University, Nathan, QLD).
Finally like to acknowledge all the patients and control subjects who kindly donated DNA to make collaborative studies like these possible.
Source of funding statement
The funding agencies did not play any role in the design of the study, in the collection, analysis, or interpretation of data, or in the writing of the report or the decision to submit the paper for publication. The corresponding authors had access to all the data in this study.
Statistical Analysis was performed by Michael G. Heckman MS (Mayo Clinic).
Author ContributionsOAR, MJF were the principal investigators and responsible for the concept and design of the study. AIO, JB, OAR, CVG were responsible for technical aspects of study. MGH, ND were responsible for all analysis. OAR, MJF were responsible for drafting of manuscript. All authors participated in study design and approach, sample collection, data acquisition, critical revision and final approval of manuscript.
Conflict of interest
The authors report no conflict of interest
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