David Crosiers

Large-scale replication and heterogeneity in Parkinson disease genetic loci

Objective: Eleven genetic loci have reached genome-wide significance in a recent meta-analysis of genome-wide association studies in Parkinson disease (PD) based on populations of Caucasian descent. The extent to which these genetic effects are consistent across different populations is unknown. Methods: Investigators from the Genetic Epidemiology of Parkinsons Disease Consortium were invited to participate in the study. A total of 11 SNPs were genotyped in 8,750 cases and 8,955 controls. Fixed as well as random effects models were used to provide the summary risk estimates for these variants. We evaluated between-study heterogeneity and heterogeneity between populations of different ancestry. Results: In the overall analysis, single nucleotide polymorphisms (SNPs) in 9 loci showed significant associations with protective per-allele odds ratios of 0.78–0.87 (LAMP3, BST1, and MAPT) and susceptibility per-allele odds ratios of 1.14–1.43 (STK39, GAK, SNCA, LRRK2, SYT11, and HIP1R). For 5 of the 9 replicated SNPs there was nominally significant between-site heterogeneity in the effect sizes (I2 estimates ranged from 39% to 48%). Subgroup analysis by ethnicity showed significantly stronger effects for the BST1 (rs11724635) in Asian vs Caucasian populations and similar effects for SNCA, LRRK2, LAMP3, HIP1R, and STK39 in Asian and Caucasian populations, while MAPT rs2942168 and SYT11 rs34372695 were monomorphic in the Asian population, highlighting the role of population-specific heterogeneity in PD. Conclusion: Our study allows insight to understand the distribution of newly identified genetic factors contributing to PD and shows that large-scale evaluation in diverse populations is important to understand the role of population-specific heterogeneity. Neurology® 2012;79:659–667

A multi-centre clinico-genetic analysis of the VPS35 gene in Parkinson disease indicates reduced penetrance for disease-associated variants

Background Two recent studies identified a mutation (p.Asp620Asn) in the vacuolar protein sorting 35 gene as a cause for an autosomal dominant form of Parkinson disease . Although additional missense variants were described, their pathogenic role yet remains inconclusive. Methods and results We performed the largest multi-center study to ascertain the frequency and pathogenicity of the reported vacuolar protein sorting 35 gene variants in more than 15,000 individuals worldwide. p.Asp620Asn was detected in 5 familial and 2 sporadic PD cases and not in healthy controls, p.Leu774Met in 6 cases and 1 control, p.Gly51Ser in 3 cases and 2 controls. Overall analyses did not reveal any significant increased risk for p.Leu774Met and p.Gly51Ser in our cohort. Conclusions Our study apart from identifying the p.Asp620Asn variant in familial cases also identified it in idiopathic Parkinson disease cases, and thus provides genetic evidence for a role of p.Asp620Asn in Parkinson disease in different populations worldwide.

Relative contribution of simple mutations vs. copy number variations in five Parkinson disease genes in the Belgian population

The relative contribution of simple mutations and copy number variations (CNVs) in SNCA, PARK2, PINK1, PARK7, and LRRK2 to the genetic etiology of Parkinson disease (PD) is still unclear because most studies did not completely analyze each gene. In a large group of Belgian PD patients (N=310) and control individuals (N=270), we determined the mutation frequency of both simple mutations and CNVs in these five PD genes, using direct sequencing, multiplex amplicon quantification (MAQ), and real‐time PCR assays. Overall, we identified 14 novel heterozygous variants, of which 11 were absent in control individuals. We observed eight PARK2 (multiple) exon multiplications in PD patients and one exon deletion in a control individual. Furthermore, we identified one SNCA whole‐gene duplication. The PARK2 and LRRK2 mutation frequencies in Belgian PD patients were similar to those reported in other studies. However, at this stage the true pathogenic nature of some heterozygous mutations in recessive genes remains elusive. Furthermore, though mutations is SNCA, PINK1, and PARK7 are rare, our identification of a SNCA duplication confirmed that screening of these genes remains meaningful. Hum Mutat 30:1–8, 2009.

Parkinson disease: Insights in clinical, genetic and pathological features of monogenic disease subtypes

In the past 15 years, insights in clinical and genetic characteristics of Parkinson disease (PD) have increased substantially. Sequence or copy number variants in at least six genes (SNCA, LRRK2, PARK2, PINK1, DJ-1 and ATP13A2) have been identified to cause monogenic forms of PD. Routine clinical testing for mutations in these genes is feasible and available, but overlapping phenotypes in monogenic and sporadic PD complicate straightforward diagnostic screening. Primarily, a positive familial history and an early onset age should prompt clinicians to consider genetic testing. Based on a literature review on clinical and neuropathological features of PD patients carrying a pathogenic mutation we propose guidelines for genetic diagnostic testing in clinical practice. However, the absence of disease-modifying therapies and the variable penetrance of most known mutations currently limit the usefulness of genetic diagnostic testing for PD in clinical practice.

DLB and PDD: a role for mutations in dementia and Parkinson disease genes?

Based on the substantial overlap in clinical and pathological characteristics of dementia with Lewy bodies (DLB) and Parkinson disease with dementia (PDD) with Alzheimer disease (AD) and Parkinson disease (PD) we hypothesized that these disorders might share underlying genetic factors. The contribution of both sequence and copy number variants (CNVs) in known AD and PD genes to the genetic etiology of DLB and PDD however is currently unclear. Therefore, we performed a gene-based mutation analysis of all major AD and PD genes in 99 DLB and 75 PDD patients, including familial and sporadic forms, from Flanders, Belgium. Also, copy number variants in APP, SNCA, and PARK2 were determined. In the AD genes we detected proven pathogenic missense mutations in PSEN1 and PSEN2, and 2 novel missense variants in PSEN2 and MAPT. In the PD genes we identified 1 SNCA duplication, the LRRK2 R1441C founder mutation and 4 novel heterozygous missense variants with unknown pathogenicity. Our results suggest a contribution of established AD and PD genes to the genetic etiology of DLB and PDD though to a limited extent. They do support the hypothesis of a genetic overlap between members of the Lewy body disease spectrum, but additional genes still have to exist.

GIGYF2 has no major role in Parkinson genetic etiology in a Belgian population

Missense mutations were identified in the Grb10-Interacting GYF Protein-2 gene (GIGYF2), located in the chromosomal region 2q36-q37, in familial Parkinson disease (PD) patients of European descent. To determine the contribution of GIGYF2 mutations in an extended (N=305) Belgian series of both familial and sporadic PD patients, we sequenced all 32 coding and non-coding exons of GIGYF2. In three sporadic PD patients we identified two novel heterozygous missense mutations (c.1907A>G, p.Tyr636Cys and c.2501G>A, p.Arg834Gln), that were absent from control individuals (N=360). However, since we lack genetic as well as functional data supporting their pathogenic nature, we cannot exclude that these variants are benign polymorphisms. Together, our results do not support a role for GIGYF2 in the genetic etiology of Belgian PD.

Global investigation and meta-analysis of the C9orf72 (G4C2)n repeat in Parkinson disease

Objectives: The objective of this study is to clarify the role of (G4C2)n expansions in the etiology of Parkinson disease (PD) in the worldwide multicenter Genetic Epidemiology of Parkinsons Disease (GEO-PD) cohort. Methods: C9orf72 (G4C2)n repeats were assessed in a GEO-PD cohort of 7,494 patients diagnosed with PD and 5,886 neurologically healthy control individuals ascertained in Europe, Asia, North America, and Australia. Results: A pathogenic (G4C2)n>60 expansion was detected in only 4 patients with PD (4/7,232; 0.055%), all with a positive family history of neurodegenerative dementia, amyotrophic lateral sclerosis, or atypical parkinsonism, while no carriers were detected with typical sporadic or familial PD. Meta-analysis revealed a small increase in risk of PD with an increasing number of (G4C2)n repeats; however, we could not detect a robust association between the C9orf72 (G4C2)n repeat and PD, and the population attributable risk was low. Conclusions: Together, these findings indicate that expansions in C9orf72 do not have a major role in the pathogenesis of PD. Testing for C9orf72 repeat expansions should only be considered in patients with PD who have overt symptoms of frontotemporal lobar degeneration/amyotrophic lateral sclerosis or apparent family history of neurodegenerative dementia or motor neuron disease.

Mindfulness Training among Individuals with Parkinson's Disease: Neurobehavioral Effects

Objective. To investigate possible neurobehavioral changes secondary to a mindfulness based intervention (MBI) training for individuals living with Parkinsons disease (PD). Background. In the context of complementary medicine, MBIs are increasingly being used for stress reduction and in patient populations coping with chronic illness. The use of alternative and complementary medicine may be higher in patients with chronic conditions such as PD. However, behavioral effects of mindfulness training in PD have not yet been reported in the literature and this points to an unmet need and warrants further examination. Methods. A total of 27 out of 30 PD patients completed a randomized controlled longitudinal trial. Questionnaires and the UPDRS I–IV were obtained at baseline and 8-week follow-up. Results. Significant changes after the MBI were found including a 5.5 point decrease on the UPDRS motor score, an increase of 0.79 points on Parkinsons disease questionnaire (PDQ-39) pain item, and a 3.15 point increase in the Five Facet Mindfulness Questionnaire observe facet. Conclusions. To the best of our knowledge, this is the first quantitative analysis of neurobehavioral effects of MBI in PD.

Contribution of VPS35 genetic variability to LBD in the Flanders-Belgian population

VPS35 was recently identified as a novel autosomal dominant gene for Parkinson disease. In this study, we aimed to determine the contribution of simple and complex VPS35 variations to the genetic etiology of the spectrum of Lewy body disorders (LBD) in a Flanders-Belgian patient cohort (n = 677). We identified 3 novel missense variations in addition to 1 silent and 1 intronic variation predicted to activate a cryptic splice site, but no copy number variations. Despite the absence of these rare variations in the control group (n = 800), we could not attain convincing evidence for pathogenicity by segregation analysis or in silico predictions. Hence, our data do not support a major role for VPS35 variations in the genetic etiology of Lewy body disorders in the Flanders-Belgian population.

Comprehensive genetic and mutation analysis of familial dementia with Lewy bodies linked to 2q35-q36.

The second most frequent form of neurodegenerative dementia after Alzheimers disease is dementia with Lewy bodies (DLB). Since informative DLB families are scarce, little is presently known about the molecular genetic etiology of DLB. We recently mapped the first locus for DLB on chromosome 2q35-q36 in a multiplex Belgian family, DR246, with autopsy-proven DLB pathology in a region of 9.2 Mb. Here, we describe the ascertainment of additional DR246 family members and significant finemapping of the DLB locus to 3.3 Mb based on informative meiotic recombinants. Extensive sequencing of the 42 positional candidate genes within the DLB region did not identify a simple pathogenic mutation that co-segregated with disease in family DR246. Also high resolution analysis of copy number variations in the DLB locus did not provide evidence for a complex mutation. In conclusion, we confirmed the DLB locus at 2q35-q36 as a genetic entity but candidate gene-based sequencing and copy number variation analysis did not identify the pathogenic mutation in family DR246. Other detection strategies will be needed to reveal the underlying mutation explaining the linkage of DLB to 2q35-q26. Possibly the disease mutation in this family acts through a more complex mechanism than generally envisaged for monogenic disorders. Nevertheless, identifying the first familial DLB gene is likely to contribute an entry point into the pathogenic cascades underlying DLB pathology.