Establishing an online resource to facilitate global collaboration and inclusion of underrepresented populations: Experience from the MJFF Global Genetic Parkinson's Disease Project

Parkinson's disease (PD) is the fastest-growing neurodegenerative disorder, currently affecting ~7 million people worldwide. PD is clinically and genetically heterogeneous, with at least 10% of all cases explained by a monogenic cause or strong genetic risk factor. However, the vast majority of our present data on monogenic PD is based on the investigation of patients of European White ancestry, leaving a large knowledge gap on monogenic PD in underrepresented populations. Gene-targeted therapies are being developed at a fast pace and have started entering clinical trials. In light of these developments, building a global network of centers working on monogenic PD, fostering collaborative research, and establishing a clinical trial-ready cohort is imperative. Based on a systematic review of the English literature on monogenic PD and a successful team science approach, we have built up a network of 59 sites worldwide and have collected information on the availability of data, biomaterials, and facilities. To enable access to this resource and to foster collaboration across centers, as well as between academia and industry, we have developed an interactive map and online tool allowing for a quick overview of available resources, along with an option to filter for specific items of interest. This initiative is currently being merged with the Global Parkinson's Genetics Program (GP2), which will attract additional centers with a focus on underrepresented sites. This growing resource and tool will facilitate collaborative research and impact the development and testing of new therapies for monogenic and potentially for idiopathic PD patients.

GWAS meta-analysis of over 29,000 people with epilepsy identifies 26 risk loci and subtype-specific genetic architecture

Epilepsy is a highly heritable disorder affecting over 50 million people worldwide, of which about one-third are resistant to current treatments. Here we report a multi-ancestry genome-wide association study including 29,944 cases, stratified into three broad categories and seven subtypes of epilepsy, and 52,538 controls. We identify 26 genome-wide significant loci, 19 of which are specific to genetic generalized epilepsy (GGE). We implicate 29 likely causal genes underlying these 26 loci. SNP-based heritability analyses show that common variants explain between 39.6% and 90% of genetic risk for GGE and its subtypes. Subtype analysis revealed markedly different genetic architectures between focal and generalized epilepsies. Gene-set analyses of GGE signals implicate synaptic processes in both excitatory and inhibitory neurons in the brain. Prioritized candidate genes overlap with monogenic epilepsy genes and with targets of current antiseizure medications. Finally, we leverage our results to identify alternate drugs with predicted efficacy if repurposed for epilepsy treatment.

ANXA1 mutation analysis in Italian patients with early onset PD

Recently, a novel pathogenic variant in Annexin A1 protein (c.4G > A, p.Ala2Thr) has been identified in an Iranian consanguineous family with autosomal recessive parkinsonism. The deficiencies of ANXA1 could lead to extracellular SNCA accumulation, defects in intracellular signaling pathways and synaptic plasticity causing parkinsonism. The aim of this study was to identify rare ANXA1 variants in 95 early-onset PD patients from South Italy. Sequencing analysis of ANXA1 gene revealed only 2 synonymous variants in PD patients (rs1050305, rs149033255). Therefore, we conclude that the recently published ANXA1 mutation is not a common cause of EOPD in Southern Italy.

Neurological manifestations in patients and disease carriers in an Italian family with osteosclerosis

BACKGROUND

Hereditary cranial hyperostosis is a rare disease never described in Italy, so the neurological manifestations in patients and carriers of the disease have been little studied.

METHODS

We describe the neurological and neuroimaging features of patients and carriers of the gene from a large Italian family with sclerosteosis.

RESULTS

In this family, genetic testing detected the homozygous p.Gln24X (c.70C > T) mutation of the SOST gene in the proband and a heterozygous mutation in 9 siblings. In homozygous adults, severe craniofacial hyperostosis was manifested by cranial neuropathy in childhood, chronic headache secondary to intracranial hypertension, and an obstructive sleep apnea syndrome in adults. In one of the adult patients, there was a compressible subcutaneous swelling in the occipital region caused by transosseous intracranial-extracranial occipital venous drainage, a compensation mechanism of obstructed venous drainage secondary to cranial hyperostosis. Mild cranial hyperostosis causing frequent headache and snoring was evident in the nine heterozygous subjects.

CONCLUSIONS

Multiple cranial neuropathies and headache in children, while severe chronic headache and sleep disturbances in adults, are the neurological manifestations of the first Italian family with osteosclerosis. It is reasonable to extend neurological and neuroimaging evaluation to gene carriers as well.

Investigation of Shared Genetic Risk Factors Between Parkinson's Disease and Cancers

BACKGROUND

Epidemiological studies that examined the association between Parkinson's disease (PD) and cancers led to inconsistent results, but they face a number of methodological difficulties.

OBJECTIVE

We used results from genome-wide association studies (GWASs) to study the genetic correlation between PD and different cancers to identify common genetic risk factors.

METHODS

We used individual data for participants of European ancestry from the Courage-PD (Comprehensive Unbiased Risk Factor Assessment for Genetics and Environment in Parkinson's Disease; PD, N = 16,519) and EPITHYR (differentiated thyroid cancer, N = 3527) consortia and summary statistics of GWASs from iPDGC (International Parkinson Disease Genomics Consortium; PD, N = 482,730), Melanoma Meta-Analysis Consortium (MMAC), Breast Cancer Association Consortium (breast cancer), the Prostate Cancer Association Group to Investigate Cancer Associated Alterations in the Genome (prostate cancer), International Lung Cancer Consortium (lung cancer), and Ovarian Cancer Association Consortium (ovarian cancer) (N comprised between 36,017 and 228,951 for cancer GWASs). We estimated the genetic correlation between PD and cancers using linkage disequilibrium score regression. We studied the association between PD and polymorphisms associated with cancers, and vice versa, using cross-phenotypes polygenic risk score (PRS) analyses.

RESULTS

We confirmed a previously reported positive genetic correlation of PD with melanoma (Gcorr = 0.16 [0.04; 0.28]) and reported an additional significant positive correlation of PD with prostate cancer (Gcorr = 0.11 [0.03; 0.19]). There was a significant inverse association between the PRS for ovarian cancer and PD (odds ratio [OR] = 0.89 [0.84; 0.94]). Conversely, the PRS of PD was positively associated with breast cancer (OR = 1.08 [1.06; 1.10]) and inversely associated with ovarian cancer (OR = 0.95 [0.91; 0.99]). The association between PD and ovarian cancer was mostly driven by rs183211 located in an intron of the NSF gene (17q21.31).

CONCLUSIONS

We show evidence in favor of a contribution of pleiotropic genes to the association between PD and specific cancers. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society. This article has been contributed to by U.S. Government employees and their work is in the public domain in the USA.

Embracing Monogenic Parkinson's Disease: The MJFF Global Genetic PD Cohort

BACKGROUND

As gene-targeted therapies are increasingly being developed for Parkinson's disease (PD), identifying and characterizing carriers of specific genetic pathogenic variants is imperative. Only a small fraction of the estimated number of subjects with monogenic PD worldwide are currently represented in the literature and availability of clinical data and clinical trial-ready cohorts is limited.

OBJECTIVE

The objectives are to (1) establish an international cohort of affected and unaffected individuals with PD-linked variants; (2) provide harmonized and quality-controlled clinical characterization data for each included individual; and (3) further promote collaboration of researchers in the field of monogenic PD.

METHODS

We conducted a worldwide, systematic online survey to collect individual-level data on individuals with PD-linked variants in SNCA, LRRK2, VPS35, PRKN, PINK1, DJ-1, as well as selected pathogenic and risk variants in GBA and corresponding demographic, clinical, and genetic data. All registered cases underwent thorough quality checks, and pathogenicity scoring of the variants and genotype-phenotype relationships were analyzed.

RESULTS

We collected 3888 variant carriers for our analyses, reported by 92 centers (42 countries) worldwide. Of the included individuals, 3185 had a diagnosis of PD (ie, 1306 LRRK2, 115 SNCA, 23 VPS35, 429 PRKN, 75 PINK1, 13 DJ-1, and 1224 GBA) and 703 were unaffected (ie, 328 LRRK2, 32 SNCA, 3 VPS35, 1 PRKN, 1 PINK1, and 338 GBA). In total, we identified 269 different pathogenic variants; 1322 individuals in our cohort (34%) were indicated as not previously published.

CONCLUSIONS

Within the MJFF Global Genetic PD Study Group, we (1) established the largest international cohort of affected and unaffected individuals carrying PD-linked variants; (2) provide harmonized and quality-controlled clinical and genetic data for each included individual; (3) promote collaboration in the field of genetic PD with a view toward clinical and genetic stratification of patients for gene-targeted clinical trials. © 2023 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

The Interaction between HLA-DRB1 and Smoking in Parkinson's Disease Revisited

BACKGROUND

Two studies that examined the interaction between HLA-DRB1 and smoking in Parkinson's disease (PD) yielded findings in opposite directions.

OBJECTIVE

To perform a large-scale independent replication of the HLA-DRB1 × smoking interaction.

METHODS

We genotyped 182 single nucleotide polymorphism (SNPs) associated with smoking initiation in 12 424 cases and 9480 controls to perform a Mendelian randomization (MR) analysis in strata defined by HLA-DRB1.

RESULTS

At the amino acid level, a valine at position 11 (V11) in HLA-DRB1 displayed the strongest association with PD. MR showed an inverse association between genetically predicted smoking initiation and PD only in absence of V11 (odds ratio, 0.74, 95% confidence interval, 0.59-0.93, PInteraction  = 0.028). In silico predictions of the influence of V11 and smoking-induced modifications of α-synuclein on binding affinity showed findings consistent with this interaction pattern.

CONCLUSIONS

Despite being one of the most robust findings in PD research, the mechanisms underlying the inverse association between smoking and PD remain unknown. Our findings may help better understand this association. © 2022 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society.

Genome-wide Association and Meta-analysis of Age at Onset in Parkinson Disease: Evidence From the COURAGE-PD Consortium

BACKGROUND AND OBJECTIVES

Considerable heterogeneity exists in the literature concerning genetic determinants of the age at onset (AAO) of Parkinson disease (PD), which could be attributed to a lack of well-powered replication cohorts. The previous largest genome-wide association studies (GWAS) identified SNCA and TMEM175 loci on chromosome (Chr) 4 with a significant influence on the AAO of PD; these have not been independently replicated. This study aims to conduct a meta-analysis of GWAS of PD AAO and validate previously observed findings in worldwide populations.

METHODS

A meta-analysis was performed on PD AAO GWAS of 30 populations of predominantly European ancestry from the Comprehensive Unbiased Risk Factor Assessment for Genetics and Environment in Parkinson's Disease (COURAGE-PD) Consortium. This was followed by combining our study with the largest publicly available European ancestry dataset compiled by the International Parkinson Disease Genomics Consortium (IPDGC).

RESULTS

The COURAGE-PD Consortium included a cohort of 8,535 patients with PD (91.9%: Europeans and 9.1%: East Asians). The average AAO in the COURAGE-PD dataset was 58.9 years (SD = 11.6), with an underrepresentation of females (40.2%). The heritability estimate for AAO in COURAGE-PD was 0.083 (SE = 0.057). None of the loci reached genome-wide significance (p < 5 × 10-8). Nevertheless, the COURAGE-PD dataset confirmed the role of the previously published TMEM175 variant as a genetic determinant of the AAO of PD with Bonferroni-corrected nominal levels of significance (p < 0.025): (rs34311866: β(SE)COURAGE = 0.477(0.203), p COURAGE = 0.0185). The subsequent meta-analysis of COURAGE-PD and IPDGC datasets (Ntotal = 25,950) led to the identification of 2 genome-wide significant association signals on Chr 4, including the previously reported SNCA locus (rs983361: β(SE)COURAGE+IPDGC = 0.720(0.122), p COURAGE+IPDGC = 3.13 × 10-9) and a novel BST1 locus (rs4698412: β(SE)COURAGE+IPDGC = -0.526(0.096), p COURAGE+IPDGC = 4.41 × 10-8).

DISCUSSION

Our study further refines the genetic architecture of Chr 4 underlying the AAO of the PD phenotype through the identification of BST1 as a novel AAO PD locus. These findings open a new direction for the development of treatments to delay the onset of PD.

Dairy Intake and Parkinson's Disease: A Mendelian Randomization Study

BACKGROUND

Previous prospective studies highlighted dairy intake as a risk factor for Parkinson's disease (PD), particularly in men. It is unclear whether this association is causal or explained by reverse causation or confounding.

OBJECTIVE

The aim is to examine the association between genetically predicted dairy intake and PD using two-sample Mendelian randomization (MR).

METHODS

We genotyped a well-established instrumental variable for dairy intake located in the lactase gene (rs4988235) within the Courage-PD consortium (23 studies; 9823 patients and 8376 controls of European ancestry).

RESULTS

Based on a dominant model, there was an association between genetic predisposition toward higher dairy intake and PD (odds ratio [OR] per one serving per day = 1.70, 95% confidence interval = 1.12-2.60, P = 0.013) that was restricted to men (OR = 2.50 [1.37-4.56], P = 0.003; P-difference with women = 0.029).

CONCLUSIONS

Using MR, our findings provide further support for a causal relationship between dairy intake and higher PD risk, not biased by confounding or reverse causation. Further studies are needed to elucidate the underlying mechanisms. © 2022 International Parkinson and Movement Disorder Society.

Multiple system atrophy and C9orf72 hexanucleotide repeat expansions in a cohort of Italian patients

Exanucleotide expansions in C9orf72 gene have been described as potential risk factor in some patients with Multiple system atrophy (MSA) and other forms of atypical parkinsonism. The goal of our study was to extend the knowledge on the involvement of C9orf72 in MSA studying a cohort of 100 patients from Italy. We identified 2 heterozygous patients in the pathological range (> 30 repeats) and 4 heterozygous patients for expansions in the premutation range (20 -30 repeats). Our findings strengthen the previously hypothesized role for this gene as a risk factor for MSA and raise the possibility of a more complex and still unknown involvement of this gene in the heterogeneity of MSA.

Mendelian Randomisation Study of Smoking, Alcohol, and Coffee Drinking in Relation to Parkinson's Disease

BACKGROUND

Previous studies showed that lifestyle behaviors (cigarette smoking, alcohol, coffee) are inversely associated with Parkinson's disease (PD). The prodromal phase of PD raises the possibility that these associations may be explained by reverse causation.

OBJECTIVE

To examine associations of lifestyle behaviors with PD using two-sample Mendelian randomisation (MR) and the potential for survival and incidence-prevalence biases.

METHODS

We used summary statistics from publicly available studies to estimate the association of genetic polymorphisms with lifestyle behaviors, and from Courage-PD (7,369 cases, 7,018 controls; European ancestry) to estimate the association of these variants with PD. We used the inverse-variance weighted method to compute odds ratios (ORIVW) of PD and 95%confidence intervals (CI). Significance was determined using a Bonferroni-corrected significance threshold (p = 0.017).

RESULTS

We found a significant inverse association between smoking initiation and PD (ORIVW per 1-SD increase in the prevalence of ever smoking = 0.74, 95%CI = 0.60-0.93, p = 0.009) without significant directional pleiotropy. Associations in participants ≤67 years old and cases with disease duration ≤7 years were of a similar size. No significant associations were observed for alcohol and coffee drinking. In reverse MR, genetic liability toward PD was not associated with smoking or coffee drinking but was positively associated with alcohol drinking.

CONCLUSION

Our findings are in favor of an inverse association between smoking and PD that is not explained by reverse causation, confounding, and survival or incidence-prevalence biases. Genetic liability toward PD was positively associated with alcohol drinking. Conclusions on the association of alcohol and coffee drinking with PD are hampered by insufficient statistical power.

Exome-wide association study of levodopa-induced dyskinesia in Parkinson's disease

Levodopa is the standard long-term dopamine replacement therapy to treat Parkinson's disease (PD) symptoms. With time, levodopa may induce debilitating dyskinesias (LID), the treatment of which represents a large clinically unmet need. However, time-to-LID onset varies between patients, reflecting a possible genetic component. We performed an hypothesis-free whole-exome sequencing (WES)-based screening of time-to-LID onset and attempted replication of previously published candidate gene studies. A WES association analysis was carried out in 134 PD patients in a meta-analytical framework. Replication was attempted in an independent study of 97 PD patients. Variants from previously reported candidate genes (OPRM1, COMT, BDNF) were also specifically examined. We significantly replicated, for the first time, an association of variant rs1799971 in the OPRM1 gene with time-to-LID onset. Furthermore, we identified two novel potentially functional variants, in the MAD2L2 (rs2233019) and MAP7 (rs35350783) genes, which were significantly associated at the discovery stage. In the replication study, the two variants showed direction-consistent effects but did not achieve the replication significance threshold. Our study provides the first WES results for time-to-LID onset, where we replicate association at OPRM1, and suggest new variants in MAD2L2 and MAP7 genes that are significant in discovery, but require larger datasets for replication. The results are being made publicly available to allow for independent external validation.

DCTN1 mutation analysis in Italian patients with PSP, MSA, and DLB

DCTN1 encodes the largest subunit of dynactin complex essential in the retrograde axonal transport and cytoplasmic transport of vesicles; mutations in DCTN1 have been reported predominantly in individuals with Perry syndrome and, recently, in patients with progressive supranuclear palsy. Our genetic screening of DCTN1 in 79 patients with progressive supranuclear palsy, 100 patients with multiple system atrophy, and 28 patients with dementia with Lewy bodies from Italy revealed only synonymous and intronic variants, suggesting that DCTN1 mutations do not have a key role in the development of atypical parkinsonism in the Italian population.

A familial t(4;8) translocation segregates with epilepsy and migraine with aura

Three relatives carrying a t(4;8)(p15.2;p23.2) translocation had juvenile myoclonic epilepsy, self‐limited photosensitive occipital epilepsy and migraine with aura. The t(4;8) translocation interrupted the coding sequence of CSMD1 gene and occurred immediately to the 3’UTR of STIM2 gene. STIM2 was overexpressed in the patient carrying the unbalanced translocation, and all three individuals had a single functional copy of CSMD1. Array CGH study disclosed that these three individuals also carried a deletion at 5q12.3 that involves the RGS7BP gene. The overall results favor the view that CSMD1, STIM2, and RGS7BP genes could contribute to epilepsy and migraine phenotypes in our family.

Ultra-Rare Genetic Variation in the Epilepsies: A Whole-Exome Sequencing Study of 17,606 Individuals

Sequencing-based studies have identified novel risk genes associated with severe epilepsies and revealed an excess of rare deleterious variation in less-severe forms of epilepsy. To identify the shared and distinct ultra-rare genetic risk factors for different types of epilepsies, we performed a whole-exome sequencing (WES) analysis of 9,170 epilepsy-affected individuals and 8,436 controls of European ancestry. We focused on three phenotypic groups: severe developmental and epileptic encephalopathies (DEEs), genetic generalized epilepsy (GGE), and non-acquired focal epilepsy (NAFE). We observed that compared to controls, individuals with any type of epilepsy carried an excess of ultra-rare, deleterious variants in constrained genes and in genes previously associated with epilepsy; we saw the strongest enrichment in individuals with DEEs and the least strong in individuals with NAFE. Moreover, we found that inhibitory GABA_A receptor genes were enriched for missense variants across all three classes of epilepsy, whereas no enrichment was seen in excitatory receptor genes. The larger gene groups for the GABAergic pathway or cation channels also showed a significant mutational burden in DEEs and GGE. Although no single gene surpassed exome-wide significance among individuals with GGE or NAFE, highly constrained genes and genes encoding ion channels were among the lead associations; such genes included CACNA1G, EEF1A2, and GABRG2 for GGE and LGI1, TRIM3, and GABRG2 for NAFE. Our study, the largest epilepsy WES study to date, confirms a convergence in the genetics of severe and less-severe epilepsies associated with ultra-rare coding variation, and it highlights a ubiquitous role for GABAergic inhibition in epilepsy etiology.

DNAJC13 mutation screening in patients with Parkinson's disease from South Italy

BACKGROUND

Parkinson's disease (PD) is the second most common neurodegenerative disorder, and the most common neurodegenerative form of parkinsonism. Recently, a pathogenic mutation (p.N855S) in DNAJC13 was linked to autosomal dominant Lewy body PD in a Dutch-German-Russian Mennonite multi-incident kindred, and was found in five additional patients. In this study, we performed a comprehensive screening of the DNAJC13 gene in familial PD and sporadic PD to assess the frequency of known and novel rare nonsynonymous variants.

METHODS

We screened 563 sporadic and 168 familial PD patients and a control series (n = 1000) for the coding region of DNAJC13.

RESULTS

Our sequencing analysis identified two carriers of the c.2708G > A (p.R903K) variant in exon 24 of DNAJC13. One of these carriers is a familial PD.

CONCLUSION

The p. R903K variant was not found in 1000 healthy controls and it is localized in a functional domain of the DNAJC13 protein. Further studies are necessary to evaluate the role of DNAJC13 variants in PD.

Large-scale assessment of polyglutamine repeat expansions in Parkinson disease

OBJECTIVES

We aim to clarify the pathogenic role of intermediate size repeat expansions of SCA2, SCA3, SCA6, and SCA17 as risk factors for idiopathic Parkinson disease (PD).

METHODS

We invited researchers from the Genetic Epidemiology of Parkinson's Disease Consortium to participate in the study. There were 12,346 cases and 8,164 controls genotyped, for a total of 4 repeats within the SCA2, SCA3, SCA6, and SCA17 genes. Fixed- and random-effects models were used to estimate the summary risk estimates for the genes. We investigated between-study heterogeneity and heterogeneity between different ethnic populations.

RESULTS

We did not observe any definite pathogenic repeat expansions for SCA2, SCA3, SCA6, and SCA17 genes in patients with idiopathic PD from Caucasian and Asian populations. Furthermore, overall analysis did not reveal any significant association between intermediate repeats and PD. The effect estimates (odds ratio) ranged from 0.93 to 1.01 in the overall cohort for the SCA2, SCA3, SCA6, and SCA17 loci.

CONCLUSIONS

Our study did not support a major role for definite pathogenic repeat expansions in SCA2, SCA3, SCA6, and SCA17 genes for idiopathic PD. Thus, results of this large study do not support diagnostic screening of SCA2, SCA3, SCA6, and SCA17 gene repeats in the common idiopathic form of PD. Likewise, this largest multicentered study performed to date excludes the role of intermediate repeats of these genes as a risk factor for PD.

A new SLC20A2 mutation identified in southern Italy family with primary familial brain calcification

BACKGROUND

Primary familial brain calcification (PFBC) is a rare neurodegenerative disease characterized by bilateral calcifications mostly located in the basal ganglia and in the thalami, cerebellum and subcortical white matter. Clinical manifestations of this disease include a large spectrum of movement disorders and neuropsychiatric disturbances. PFBC is genetically heterogeneous and typically transmitted in an autosomal dominant fashion. Three causative genes have been reported: SLC20A2, PDGFRB and PDGFB.

OBJECTIVE

We screened three PFBC Italian families for mutations in the SLC20A2, PDGFRB and PDGFB genes.

METHODS

Phenotypic data were obtained by neurologic examination, CT scan and magnetic resonance imaging. Mutation screening of SLC20A2, PDGFRB and PDGFB was performed by sequencing.

RESULTS

We identified a new heterozygous deletion c.21_21delG (p.L7Ffs*10) in SLC20A2 gene in one of these families. No mutations were detected in the other two families.

CONCLUSIONS

Our data confirm that mutations in SLC20A2 are a major cause of familial idiopathic basal ganglia calcification.

C19orf12 gene mutations in patients with neurodegeneration with brain iron accumulation

A novel subtype of Neurodegeneration with Brain Iron Accumulation (NBIA) recently has been described: mitochondrial membrane protein-associated neurodegeneration (MPAN), caused by mutations of c19orf12 gene. We present phenotypic data and results of screening of C19orf12 in five unrelated NBIA families. Our data led to identify novel pathogenic mutations in C19orf12.

TREM2 R47H variant and risk of essential tremor: a cross-sectional international multicenter study

INTRODUCTION

Essential tremor (ET) is the most frequent movement disorder in adults. Its pathophysiology is not clearly understood, however there is growing evidence showing common etiologic factors with other neurodegenerative disorders such as Alzheimer's and Parkinson's diseases (AD, PD). Recently, a rare p.R47H substitution (rs75932628) in the TREM2 protein (triggering receptor expressed on myeloid cells 2; OMIM: *605086) has been proposed as a risk factor for AD, PD and amyotrophic lateral sclerosis (ALS). The objective of the study was to determine whether TREM2 p.R47H allele is also a risk factor for developing ET.

METHODS

This was a cross-sectional multicenter international study. An initial case-control cohort from Spain (n = 456 ET, n = 2715 controls) was genotyped. In a replication phase, a case-control series (n = 897 ET, n = 1449 controls) from different populations (Italy, Germany, North-America and Taiwan) was studied. Owed to the rarity of the variant, published results on p.R47H allele frequency from 14777 healthy controls from European, North American or Chinese descent were additionally considered. The main outcome measure was p.R47H (rs75932628) allelic frequency.

RESULTS

There was a significant association between TREM2 p.R47H variant and ET in the Spanish cohort (odds ratio [OR], 5.97; 95% CI, 1.203-29.626; p = 0.042), but it was not replicated in other populations.

CONCLUSIONS

These results argue in favor of population-specific differences in the allelic distribution and suggest that p.R47H (rs75932628) variant may contribute to the susceptibility of ET in Spanish population. However, taking into account the very low frequency of p.R47H, further confirmatory analyses of larger ET series are needed.

Genetic associations of Nrf2-encoding NFE2L2 variants with Parkinson's disease - a multicenter study

BACKGROUND

The transcription factor Nrf2, encoded by the NFE2L2 gene, is an important regulator of the cellular protection against oxidative stress. Parkinson's disease is a neurodegenerative disease highly associated with oxidative stress. In a previously published study, we reported associations of NFE2L2 haplotypes with risk and age at onset of idiopathic Parkinson's disease in a Swedish discovery material and a Polish replication material. Here, we have extended the replication study and performed meta-analyses including the Polish material and four new independent European patient-control materials. Furthermore, all SNPs included in the haplotype windows were investigated individually for associations with Parkinson's disease in meta-analyses including all six materials.

METHODS

Totally 1038 patients and 1600 control subjects were studied. Based on previous NFE2L2 haplotype associations with Parkinson's disease, five NFE2L2 tag SNPs were genotyped by allelic discrimination and three functional NFE2L2 promoter SNPs were genotyped by sequencing. The impact of individual SNPs and haplotypes on risk and age at onset of Parkinson's disease were investigated in each material individually and in meta-analyses of the obtained results.

RESULTS

Meta-analyses of NFE2L2 haplotypes showed association of haplotype GAGCAAAA, including the fully functional promoter haplotype AGC, with decreased risk (OR = 0.8 per allele, p = 0.012) and delayed onset (+1.1 years per allele, p = 0.048) of Parkinson's disease. These results support the previously observed protective effect of this haplotype in the first study. Further, meta-analyses of the SNPs included in the haplotypes revealed four NFE2L2 SNPs associated with age at onset of Parkinson's disease (rs7557529 G > A, -1.0 years per allele, p = 0.042; rs35652124 A > G, -1.1 years per allele, p = 0.045; rs2886161 A > G, -1.2 years per allele, p = 0.021; rs1806649 G > A, +1.2 years per allele, p = 0.029). One of these (rs35652124) is a functional SNP located in the NFE2L2 promoter. No individual SNP was associated with risk of Parkinson's disease.

CONCLUSION

Our results support the hypothesis that variation in the NFE2L2 gene, encoding a central protein in the cellular protection against oxidative stress, may contribute to the pathogenesis of Parkinson's disease. Functional studies are now needed to explore these results further.

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 Parkinson's 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.

An exome study of Parkinson's disease in Sardinia, a Mediterranean genetic isolate

Parkinson's disease (PD) is a common neurodegenerative disorder of complex aetiology. Rare, highly penetrant PD-causing mutations and common risk factors of small effect size have been identified in several genes/loci. However, these mutations and risk factors only explain a fraction of the disease burden, suggesting that additional, substantial genetic determinants remain to be found. Genetically isolated populations offer advantages for dissecting the genetic architecture of complex disorders, such as PD. We performed exome sequencing in 100 unrelated PD patients from Sardinia, a genetic isolate. SNPs absent from dbSNP129 and 1000 Genomes, shared by at least five patients, and of functional effects were genotyped in an independent Sardinian case-control sample (n = 500). Variants associated with PD with nominal p value <0.05 and those with odds ratio (OR) ≥3 were validated by Sanger sequencing and typed in a replication sample of 2965 patients and 2678 controls from Italy, Spain, and Portugal. We identified novel moderately rare variants in several genes, including SCAPER, HYDIN, UBE2H, EZR, MMRN2 and OGFOD1 that were specifically present in PD patients or enriched among them, nominating these as novel candidate risk genes for PD, although no variants achieved genome-wide significance after Bonferroni correction. Our results suggest that the genetic bases of PD are highly heterogeneous, with implications for the design of future large-scale exome or whole-genome analyses of this disease.

Frequency of the ASP620ASN mutation in VPS35 and Arg1205His mutation in EIF4G1 in familial Parkinson's disease from South Italy

Parkinson's disease (PD) is characterized by progressive loss of dopaminergic neurons in the substantia nigra pars compacta. This degeneration leads to bradykinesia, muscular rigidity, resting tremor, and postural instability. It affects 1%-2% of the population above the age of 60 years. Recently, 2 studies identified the Asp620Asn mutation in the vacuolar protein sorting 35 (VPS35) gene, and the Arg1205His in the eukaryotic translation initiation factor 4 gamma 1 gene (EIF4G1) were reported to be associated an autosomal dominant form of PD. In this study we screened these mutations in a cohort of 250 South Italy patients with familial PD and 250 control subjects from South Italy. VPS35 Asp620Asn mutation and EIF4G1 Arg1205His mutation were not found in our 250 PD patients. This result, with our previous reports on the absence of mutations in LRRK2 and in SNCA, warrant a continuing search for novel causative genes for PD among South Italy.

Alpha-synuclein repeat variants and survival in Parkinson's disease

OBJECTIVES

To determine whether α-synuclein dinucleotide repeat (REP1) genotypes are associated with survival in Parkinson's disease (PD).

METHODS

Investigators from the Genetic Epidemiology of Parkinson's Disease Consortium provided REP1 genotypes and baseline and follow-up clinical data for cases. The primary outcome was time to death. Cox proportional hazards regression models were used to assess the association of REP1 genotypes with survival.

RESULTS

Twenty-one sites contributed data for 6,154 cases. There was no significant association between α-synuclein REP1 genotypes and survival in PD. However, there was a significant association between REP1 genotypes and age at onset of PD (hazard ratio: 1.06; 95% confidence interval: 1.01-1.10; P value = 0.01).

CONCLUSIONS

In our large consortium study, α-synuclein REP1 genotypes were not associated with survival in PD. Further studies of α-synuclein's role in disease progression and long-term outcomes are needed.

A multicenter study of glucocerebrosidase mutations in dementia with Lewy bodies

IMPORTANCE

While mutations in glucocerebrosidase (GBA1) are associated with an increased risk for Parkinson disease (PD), it is important to establish whether such mutations are also a common risk factor for other Lewy body disorders.

OBJECTIVE

To establish whether GBA1 mutations are a risk factor for dementia with Lewy bodies (DLB). DESIGN We compared genotype data on patients and controls from 11 centers. Data concerning demographics, age at onset, disease duration, and clinical and pathological features were collected when available. We conducted pooled analyses using logistic regression to investigate GBA1 mutation carrier status as predicting DLB or PD with dementia status, using common control subjects as a reference group. Random-effects meta-analyses were conducted to account for additional heterogeneity.

SETTING

Eleven centers from sites around the world performing genotyping.

PARTICIPANTS

Seven hundred twenty-one cases met diagnostic criteria for DLB and 151 had PD with dementia. We compared these cases with 1962 controls from the same centers matched for age, sex, and ethnicity.

MAIN OUTCOME MEASURES

Frequency of GBA1 mutations in cases and controls. RESULTS We found a significant association between GBA1 mutation carrier status and DLB, with an odds ratio of 8.28 (95% CI, 4.78-14.88). The odds ratio for PD with dementia was 6.48 (95% CI, 2.53-15.37). The mean age at diagnosis of DLB was earlier in GBA1 mutation carriers than in noncarriers (63.5 vs 68.9 years; P < .001), with higher disease severity scores.

CONCLUSIONS AND RELEVANCE

Mutations in GBA1 are a significant risk factor for DLB. GBA1 mutations likely play an even larger role in the genetic etiology of DLB than in PD, providing insight into the role of glucocerebrosidase in Lewy body disease.

Protective effect of LRRK2 p.R1398H on risk of Parkinson's disease is independent of MAPT and SNCA variants

The best validated susceptibility variants for Parkinson's disease are located in the α-synuclein (SNCA) and microtubule-associated protein tau (MAPT) genes. Recently, a protective p.N551K-R1398H-K1423K haplotype in the leucine-rich repeat kinase 2 (LRRK2) gene was identified, with p.R1398H appearing to be the most likely functional variant. To date, the consistency of the protective effect of LRRK2 p.R1398H across MAPT and SNCA variant genotypes has not been assessed. To address this, we examined 4 SNCA variants (rs181489, rs356219, rs11931074, and rs2583988), the MAPT H1-haplotype-defining variant rs1052553, and LRRK2 p.R1398H (rs7133914) in Caucasian (n = 10,322) and Asian (n = 2289) series. There was no evidence of an interaction of LRRK2 p.R1398H with MAPT or SNCA variants (all p ≥ 0.10); the protective effect of p.R1398H was observed at similar magnitude across MAPT and SNCA genotypes, and the risk effects of MAPT and SNCA variants were observed consistently for LRRK2 p.R1398H genotypes. Our results indicate that the association of LRRK2 p.R1398H with Parkinson's disease is independent of SNCA and MAPT variants, and vice versa, in Caucasian and Asian populations.

Population-specific frequencies for LRRK2 susceptibility variants in the Genetic Epidemiology of Parkinson's Disease (GEO-PD) Consortium

BACKGROUND

Variants within the leucine-rich repeat kinase 2 gene are recognized as the most frequent genetic cause of Parkinson's disease. Leucine-rich repeat kinase 2 variation related to disease susceptibility displays many features that reflect the nature of complex, late-onset sporadic disorders like Parkinson's disease.

METHODS

The Genetic Epidemiology of Parkinson's Disease Consortium recently performed the largest genetic association study for variants in the leucine-rich repeat kinase 2 gene across 23 different sites in 15 countries.

RESULTS

Herein, we detail the allele frequencies for the novel risk factors (p.A419V and p.M1646T) and the protective haplotype (p.N551K-R1398H-K1423K) nominated in the original publication. Simple population allele frequencies not only can provide insight into the clinical relevance of specific variants but also can help genetically define patient groups.

CONCLUSIONS

Establishing individual patient-based genomic susceptibility profiles that incorporate both risk factors and protective factors will determine future diagnostic and treatment strategies.

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.

Divergent effects of the T1174S SCN1A mutation associated with seizures and hemiplegic migraine

PURPOSE

To report the identification of the T1174S SCN1A (NaV 1.1) mutation in a three-generation family with both epileptic and familial hemiplegic migraine (FHM) phenotypes and clarify the pathomechanism.

METHODS

The five affected individuals underwent detailed clinical analyses. Mutation analyses was performed by direct sequencing of SCN1A; functional studies by expression in tsA-201 cells. A computational model was used to compare the effects of T1174S with those of a typical FHM mutation (Q1489K).

KEY FINDINGS

The proband had benign occipital epilepsy (BOE); two relatives had simple febrile seizures (FS) and later developed BOE. Two additional relatives had FHM without epilepsy or FS. All affected members and one obliged carrier carried the T1174S mutation. Functional effects were divergent: positive shift of the activation curve and deceleration of recovery from fast inactivation, consistent with loss of function, and increase of persistent current (I(NaP)), consistent with gain of function. The I(NaP) increase was inhibited by dialysis of the cytoplasm, consistent with a modulation. Therefore, as shown by the computational model, T1174S could in some conditions induce overall loss of function, and in others gain of function; Q1489K induced gain of function in all the conditions.

SIGNIFICANCE

Modulation of the properties of T1174S can lead to a switch between overall gain and loss of function, consistent with a switch between promigraine end epileptogenic effect and, thus, with coexistence of epileptic and FHM phenotypes in the same family. These findings may help to shed light on the complex genotype-phenotype relationship of SCN1A mutations.

Homozygous c.649dupC mutation in PRRT2 worsens the BFIS/PKD phenotype with mental retardation, episodic ataxia, and absences

Heterozygous mutations of PRRT2, which encodes proline-rich transmembrane protein 2, are associated with heterogeneous phenotypes including benign familial infantile seizures (BFIS), or familial paroxysmal kinesigenic dystonia (PKD). We report a consanguineous Italian family with BFIS/PKD phenotype that contained 14 living members with 6 affected individuals (four men, ranging in age from 6-44 years). We identified the reported c.649dupC (p.Arg217ProfsX8) mutation of PRRT2 gene that cosegregated with the disease and was not observed in 100 controls of matched ancestry. Four patients with BFIS phenotype were heterozygous for this mutation, including the consanguineous parents of the two affected brothers with more severe phenotypes of BFIS/PKD--mental retardation, episodic ataxia, and absences--who were the only individuals to carry a homozygous c.649dupC mutation. This family provides strong evidence that homozygous PRRT2 mutations give rise to more severe clinical disease of mental retardation, episodic ataxia, and absences, and, thus, enlarges the clinical spectrum related to PRRT2 mutations. Moreover, it suggests an additive effect of double dose of the genetic mutation and underscores the complexity of the phenotypic consequences of mutations in this gene.

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 Parkinson's 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 (I(2) 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.

Spinocerebellar ataxia type 7: report of a new Italian family

Spinocerebellar ataxia type 7 (SCA7) is a neurodegenerative disorder characterized by degeneration of the cerebellum, brainstem and retina. We herein describe a family from southern Italy whose proband was a 49-year-old man presenting with ataxia with progressive gait disturbances, clumsiness and visual impairment. A molecular analysis identified 38 cytosine-adenine-guanine (CAG) repeat expansions within the SCA7 gene. Our study confirms the marked anticipation previously observed in SCA7 and extends the small number of patients studied thus far. In this family, the disease is most likely caused by a de novo expansion of a premutated intermediate allele carried by one parent.