The Genetic Architecture of Parkinson Disease in Spain: Characterizing Population-Specific Risk, Differential Haplotype Structures, and Providing Etiologic Insight.

BACKGROUND: The Iberian Peninsula stands out as having variable levels of population admixture and isolation, making Spain an interesting setting for studying the genetic architecture of neurodegenerative diseases. OBJECTIVES: To perform the largest PD genome-wide association study restricted to a single country. METHODS: We performed a GWAS for both risk of PD and age at onset in 7,849 Spanish individuals. Further analyses included population-specific risk haplotype assessments, polygenic risk scoring through machine learning, Mendelian randomization of expression, and methylation data to gain insight into disease-associated loci, heritability estimates, genetic correlations, and burden analyses. RESULTS: We identified a novel population-specific genome-wide association study signal at PARK2 associated with age at onset, which was likely dependent on the c.155delA mutation. We replicated four genome-wide independent signals associated with PD risk, including SNCA, LRRK2, KANSL1/MAPT, and HLA-DQB1. A significant trend for smaller risk haplotypes at known loci was found compared to similar studies of non-Spanish origin. Seventeen PD-related genes showed functional consequence by two-sample Mendelian randomization in expression and methylation data sets. Long runs of homozygosity at 28 known genes/loci were found to be enriched in cases versus controls. CONCLUSIONS: Our data demonstrate the utility of the Spanish risk haplotype substructure for future fine-mapping efforts, showing how leveraging unique and diverse population histories can benefit genetic studies of complex diseases. The present study points to PARK2 as a major hallmark of PD etiology in Spain. © 2019 International Parkinson and Movement Disorder Society.

GDNF gene is associated with tourette syndrome in a family study.

BACKGROUND: Tourette syndrome is a disorder characterized by persistent motor and vocal tics, and frequently accompanied by the comorbidities attention deficit hyperactivity disorder and obsessive-compulsive disorder. Impaired synaptic neurotransmission has been implicated in its pathogenesis. Our aim was to investigate the association of 28 candidate genes, including genes related to synaptic neurotransmission and neurotrophic factors, with Tourette syndrome. METHODS: We genotyped 506 polymorphisms in a discovery cohort from the United States composed of 112 families and 47 unrelated singletons with Tourette syndrome (201 cases and 253 controls). Genes containing significant polymorphisms were imputed to fine-map the signal(s) to potential causal variants. Allelic analyses in Tourette syndrome cases were performed to check the role in attention deficit hyperactivity disorder and obsessive-compulsive disorder comorbidities. Target polymorphisms were further studied in a replication cohort from southern Spain composed of 37 families and three unrelated singletons (44 cases and 73 controls). RESULTS: The polymorphism rs3096140 in glial cell line-derived neurotrophic factor gene (GDNF) was significant in the discovery cohort after correction (P = 1.5 × 10(-4) ). No linkage disequilibrium was found between rs3096140 and other functional variants in the gene. We selected rs3096140 as target polymorphism, and the association was confirmed in the replication cohort (P = 0.01). No association with any comorbidity was found. CONCLUSIONS: As a conclusion, a common genetic variant in GDNF is associated with Tourette syndrome. A defect in the production of GDNF could compromise the survival of parvalbumin interneurons, thus altering the excitatory/inhibitory balance in the corticostriatal circuitry. Validation of this variant in other family cohorts is necessary.

Lack of validation of variants associated with cervical dystonia risk: a GWAS replication study.

BACKGROUND: A recent genome-wide association study (GWAS) has identified a putative association, not statistically confirmed, of cervical dystonia within several regions in a British population. Hence, the authors proposed dysfunction of the ion channel NALCN (for sodium leak channel, nonselective) as a plausible cause of cervical dystonia. The objective of our study was to investigate the association of five single nucleotide polymorphisms (SNPs) previously reported with high signals as putative genetic risk factors for cervical dystonia in a British GWAS, including two located in the NALCN gene region. METHODS: We performed a case-control association study in a Spanish population. The SNPs selected for genotyping were two SNPS in the NALCN gene (rs61973742 and rs1338041), one SNP in the OR4X2 gene (rs67863238), one SNP in the COL4A1 region (rs619152), and one intergenic SNP (rs1249277). Genomic DNA was collected from 252 patients with cervical dystonia, with a mean age of 55.3 ± 14.1 years (mean age at onset, 43.5 ± 15.7 years), and 342 unrelated control subjects with a mean age of 56.3 ± 14.3 years. Genotyping of SNPs was performed using TaqMan assays and SimpleProbe assays. RESULTS: The SNP rs619152 had to be excluded because of assay failure. No significant differences were found in allele distribution between cases and controls for all analyzed SNPs. Therefore, we found no association with cervical dystonia for the analyzed SNPs in our Spanish population. CONCLUSIONS: We did not find any evidence supporting the association of NALCN with cervical dystonia, indicating that this gene is not implicated in the pathogenesis of this disorder in our cervical dystonia population.

BDNF Val66Met polymorphism in primary adult-onset dystonia: a case-control study and meta-analysis.

BACKGROUND: A polymorphism in brain-derived neurotrophic factor (BDNF) (Val66Met) has been reported as a risk factor in primary dystonia. However, overall the results have been inconclusive. Our aim was to clarify the association of Val66Met with primary dystonia, and with the most prevalent clinical subtypes, cervical dystonia and blepharospasm. METHODS: We conducted a Spanish multicenter case-control study (including 680 primary dystonia patients and 788 healthy controls) and performed a meta-analysis integrating our study and six previously published studies (including a total of 1,936 primary dystonia patients and 2,519 healthy controls). RESULTS: We found no allelic or genotypic association with primary dystonia, cervical dystonia, or blepharospasm risks, for the allele A (Met) from a BDNF Val66Met polymorphism in our case-control study. This was confirmed by results from our meta-analysis in white and mixed ethnic populations in any genetic model. CONCLUSION: We did not find any evidence supporting the association of the BDNF Val66Met polymorphism with primary dystonia.

Role of ATP10B in Parkinson disease in a cohort from southern Spain.

The ATP10B gene has been proposed to play an important role in the development of early-onset Parkinson's disease (PD). Nevertheless, various studies have presented controversial conclusions regarding the involvement of this gene in PD. Here, we screened 1162 patients with PD, employing a targeted resequencing approach to investigate the putative relevance of this gene in a large independent cohort of these patients from southern Spain. Variations were classified according to the American College of Medical Genetics and Genomics criteria. Association studies were performed using data of a representative healthy Spanish population from the Medical Genome Project. Frequent variants were excluded. A total of 68 variants (rare or very rare) were detected in our cohort. Among ATP10B variant carriers, 12.9 % were putative compound heterozygous carriers; of these, 25 % were patients with early-onset PD. No evidence of a relation between any rare variants of ATP10B and PD risk was observed. Therefore, our results do not support a role for ATP10B in the onset of PD, or in the risk of developing it.

Homocysteine levels, genetic background, and cognitive impairment in Parkinson's disease.

BACKGROUND: Hyperhomocysteinemia is considered an independent risk factor for cognitive impairment. OBJECTIVE: To study the correlation between homocysteine levels and cognitive impairment in patients with PD. METHODS: We conducted a case-control study that included 246 patients with PD, of whom 32 were cognitively impaired. The levels of homocysteine, folate, and vitamin B12 were measured in peripheral blood. Multivariate logistic regression analysis was applied to determine differences in homocysteine levels between PD patients with and without cognitive impairment. A meta-analysis was performed to clarify the role of Hcy levels in PD with cognitive decline. Five polymorphisms in genes involved in Hcy metabolism, including MTHFR rs1801133 and rs1801131, COMT rs4680, MTRR rs1801394, and TCN2 rs1801198, were genotyped. RESULTS: Our case-control study showed that homocysteine levels were associated with cognitive impairment in PD after adjusting for possible confounding factors such as levodopa equivalent daily dose. The results of our meta-analysis further supported the positive association between homocysteine levels and cognition in PD. We found that the MTHFR rs1801133 TT genotype led to higher homocysteine levels in PD patients, whereas the MTHFR rs1801131 CC genotype resulted in higher folate levels. However, the polymorphisms studied were not associated with cognitive impairment in PD. CONCLUSIONS: Increased homocysteine levels were a risk factor for cognitive decline in PD. However, no association was found between polymorphisms in genes involved in homocysteine metabolism and cognitive impairment in PD. Large-scale studies of ethnically diverse populations are required to definitively assess the relationship between MTHFR and cognitive impairment in PD.

Peripheral inflammatory immune response differs among sporadic and familial Parkinson's disease.

Peripheral inflammatory immune responses are thought to play a major role in the pathogenesis of Parkinson's disease (PD). The neutrophil-to-lymphocyte ratio (NLR), a biomarker of systemic inflammation, has been reported to be higher in patients with PD than in healthy controls (HCs). The present study was aimed at determining if the peripheral inflammatory immune response could be influenced by the genetic background of patients with PD. We included a discovery cohort with 222 patients with PD (132 sporadic PD, 44 LRRK2-associated PD (with p.G2019S and p.R1441G variants), and 46 GBA-associated PD), as well as 299 HCs. Demographic and clinical data were recorded. Leukocytes and their subpopulations, and the NLR were measured in peripheral blood. Multivariate lineal regression and post-hoc tests were applied to determine the differences among the groups. Subsequently, a replication study using the Parkinson's Progression Markers Initiative cohort was performed which included 401 patients with PD (281 sPD patients, 66 LRRK2-PD patients, 54 GBA-PD patients) and a group of 174 HCs. Patients with sporadic PD and GBA-associated PD showed a significantly lower lymphocyte count, a non-significantly higher neutrophil count and a significantly higher NLR than HCs. The peripheral inflammatory immune response of patients with LRRK2-associated PD did not differ from HCs. Our study supports the involvement of a peripheral inflammatory immune response in the pathophysiology of sPD and GBA-associated PD. However, this inflammatory response was not found in LRRK2-associated PD, probably reflecting different pathogenic inflammatory mechanisms.

TMEM230 in Parkinson's disease in a southern Spanish population.

TMEM230 has been associated with autosomal dominant Parkinson's disease (PD). Subsequent studies have remained negative, and none of previous described mutation has been reported anymore. We investigated the implication of this gene in the PD in a population of 703 PD patients and 695 unrelated healthy controls from southern Spain. Thirteen variants were found, twelve of them observed only in controls or in patients and controls, and one (c.190A>G) observed only in one patient. Subsequent analysis of this variant indicates that probably it is not pathogenic. In addition, we found a variation in the 3'-UTR (rs183551373) and related with the miRNA hsa-miR-4299 but it was observed only in healthy controls. Our results suggest that variants in TMEM230 gene are not associated with the development of PD.

Genetic analysis of CHCHD2 in a southern Spanish population.

Researching genetic factors involved in Parkinson's disease (PD) is crucial to increase our knowledge about the pathophysiology of the disorder. A missense mutation has recently been reported within CHCHD2, a gene newly associated with autosomal dominant PD. Subsequent studies in different ethnic populations have not reached any conclusive result about the role of CHCHD2 in PD. Therefore, the aim of this study was to investigate the implication of this gene for a PD population from southern Spain (including 536 PD patients and 518 unrelated control subjects). We studied all 4 exons of CHCHD2 and their exon-intron boundary regions. Four variants were observed in non-coding regions. No significant differences were observed in the allele frequencies of these variants between patients and controls. Thus, our study suggests that CHCHD2 is probably not involved in the etiopathogenesis of PD in our population.

Genetic factors influencing frontostriatal dysfunction and the development of dementia in Parkinson's disease.

The dual syndrome hypothesis for cognitive impairment in Parkinson's disease (PD) establishes a dichotomy between a frontrostriatal dopamine-mediated syndrome, which leads to executive deficits, and a posterior cortical syndrome, which leads to dementia. Certain genes have been linked to these syndromes although the exact contribution is still controversial. The study's objective was to investigate the role of APOE, MAPT, COMT, SNCA and GBA genes in the dual syndromes. We genotyped APOE (rs429358 and rs7412), MAPT (rs9468), COMT (rs4680) and SNCA (rs356219) risk polymorphisms and sequenced GBA in a cohort of 298 PD patients. The degree of dopaminergic depletion was investigated with [123I]FP-CIT SPECTs and the presence of dementia was ascertained with a long-term review based on established criteria. The association between genetic and imaging parameters was studied with linear regression, and the relationship with dementia onset with Cox regression. We found that APOE2 allele (Pput = 0.002; Pcau = 0.01), the minor allele 'G' in SNCA polymorphism (Pput = 0.02; Pcau = 0.006) and GBA deleterious variants in (Pput = 0.01; Pcau = 0.001) had a detrimental effect on striatal [123I]FP-CIT uptake in PD. Conversely, Met/Met carriers in COMT polymorphism had increased caudate uptake (Pcau = 0.03). The development of dementia was influenced by APOE4 allele (HR = 1.90; P = 0.03) and GBA deleterious variants (HR = 2.44; P = 0.01). Finally, we observed no role of MAPT locus in any of the syndromes. As a conclusion, APOE2, SNCA, COMT and GBA influence frontostriatal dysfunction whereas APOE4 and GBA influence the development of dementia, suggesting a double-edged role of GBA. The dichotomy of the dual syndromes may be driven by a broad dichotomy in these genetic factors.

GBA Variants Influence Motor and Non-Motor Features of Parkinson's Disease.

The presence of mutations in glucocerebrosidase (GBA) gene is a known factor increasing the risk of developing Parkinson's disease (PD). Mutations carriers have earlier disease onset and are more likely to develop neuropsychiatric symptoms than other sporadic PD cases. These symptoms have primarily been observed in Parkinson's patients carrying the most common pathogenic mutations L444P and N370S. However, recent findings suggest that other variants across the gene may have a different impact on the phenotype as well as on the disease progression. We aimed to explore the influence of variants across GBA gene on the clinical features and treatment related complications in PD. In this study, we screened the GBA gene in a cohort of 532 well-characterised PD patients and 542 controls from southern Spain. The potential pathogeniticy of the identified variants was assessed using in-silico analysis and subsequently classified as benign or deleterious. As a result, we observed a higher frequency of GBA variants in PD patients (12.2% vs. 7.9% in controls, p = 0.021), earlier mean age at disease onset in GBA variant carriers (50.6 vs. 56.6 years; p = 0.013), as well as more prevalent motor and non-motor symptoms in patients carrying deleterious variants. In addition, we found that dopaminergic motor complications are influenced by both benign and deleterious variants. Our results highlight the fact that the impact on the phenotype highly depends on the potential pathogenicity of the carried variants. Therefore, the course of motor and non-motor symptoms as well as treatment-related motor complications could be influenced by GBA variants.

Systematic mutational analysis of FBXO7 in a Parkinson's disease population from southern Spain.

Mutations in FBXO7 (PARK15) have been associated with a syndrome characterized by early-onset progressive parkinsonism with and without pyramidal tract signs. Therefore, our aim was to analyze this gene in a population from southern Spain (338 Parkinson's disease [PD] patients and 330 unrelated control subjects) to elucidate the potential involvement of FBXO7 in PD pathogenesis. We identified 17 variants (11 novel), including 10 missense substitutions, 3 synonymous, and 4 intronic alterations. Six substitutions were described as putatively damaging by the bioinformatics tools and 1 intronic variation was described to affect splicing. Minor allele frequencies of the highly polymorphic coding single nucleotide polymorphisms (SNPs) in PD patients and control subjects were similar. All rare variants were heterozygous. No deletions or duplications involving FBXO7 exons were identified. Our results suggest that the involvement of the FBXO7 gene in PD is very rare, at least in this population from southern Spain.

Genetic association of sirtuin genes and Parkinson's disease.

Parkinson's disease (PD) is a neurodegenerative disease caused by both genetic and environmental factors. Sirtuins are highly-conserved, NAD-dependent class III deacetylases that regulate a variety of cellular functions. Most of the known sirtuins have been involved in animal models of neurodegenerative disorders, such as PD. Although seven sirtuin family members have been identified (SIRT1-SIRT7) the relationship between sirtuins and PD in humans has not been established. Our aim was to investigate the association between sirtuin genes and risk of PD. We included 326 PD patients and 371 controls from southern Spain. Forty-one single nucleotide polymorphisms (SNPs) in sirtuin genes were genotyped in order to determine whether they were related to the risk of PD. These SNPs included Tag-SNPs, coding non-synonymous SNPs and SNPs affecting activity of microRNA binding sites. No relationship was found between these SNPs in sirtuin genes and PD. Our data indicate that variations in sirtuin genes do not affect the risk for PD, at least in our population.