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.

Low serum uric acid levels in progressive supranuclear palsy.

INTRODUCTION: Uric acid is a natural antioxidant, and it has been shown that low levels of uric acid could be a risk factor for the development of PD. Our aim was to investigate whether uric acid plays a role in PSP. METHODS: We carried out a cross-sectional study to compare serum uric acid levels between PSP patients, PD patients, and healthy controls. We also analyzed longitudinal uric acid levels in the PSP group. RESULTS: PSP patients showed reduced levels of serum uric acid as compared to healthy controls. This reduction was similar to that found in patients with PD. Uric acid levels of PSP patients did not change with time. CONCLUSION: Serum uric acid levels are reduced in PSP as well as in PD compared to healthy controls. Our data suggest that high levels of uric acid could be a natural protective factor against PSP.

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.

The use of botulinum toxin in the treatment of sialorrhea in parkinsonian disorders.

Drooling is a common symptom in parkinsonian disorders. Our aim was to assess the safety and effect of botulinum toxin when applied to parotid glands without ultrasound guidance for sialorrhea in parkinsonian disorders in a retrospective study with a long-term follow-up. We evaluated 53 patients (64.2% male and 35.8% female) with a mean age of 70.18 ± 9.25 years who were treated in our centre between 2007 and 2013. We analysed the mean dose, latency, effect duration, response and adverse effects of treating sialorrhea by injecting botulinum toxin type A (Botox) into the parotid glands without ultrasound guidance. A total of 41 patients with Parkinson's disease, 6 with progressive supranuclear palsy, 4 with multiple system atrophy and 2 with corticobasal degeneration were included. The mean duration of the disease at onset was 10.51 ± 6.81 years and the mean sialorrhea duration was 1.99 ± 1.55 years. The initial dose used for each parotid gland was 14.53 ± 3.95 units of Botox, with a mean dose of 22.17 ± 8.76 units. There was an improvement after treatment in 65.22% of patients with an average score of 6.85 ± 1.58 points on a scale from 0 to 10. The duration of the treatment effect was 4.38 ± 2.11 months, with a latency period of 10.06 ± 9.63 days. Adverse effects were mild and infrequent. Botulinum toxin is a safe and effective therapy for the treatment of sialorrhea in parkinsonian disorders and there is no requirement for ultrasound guidance. It has a rapid onset and lasting effect without requiring a high dosage.

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.

Increased bilirubin levels in Parkinson's disease.

INTRODUCTION: Oxidative stress plays a key role in Parkinson's disease (PD) etiopathology. Heme oxygenase, an important enzyme which regulates oxidative balance, converts heme molecules into carbon monoxide, iron and biliverdin/bilirubin. The role of bilirubin has not been fully studied in PD, showing controversial results over the last few decades. Our aim was to investigate the relationship between bilirubin levels and PD. Secondly, we sought to evaluate the link between bilirubin concentration with PD progression, severity and dopaminergic treatment. METHODS: We included 420 PD patients (56% males, mean age: 64 ±â€¯12 years) and 435 healthy controls (47% males, mean age: 58 ±â€¯17 years). Bilirubin levels in both groups were compared using linear regression and multivariate analysis adjusted according to age and sex. Secondly, a case study with the PD cohort was carried out and bilirubin levels were correlated with current treatment, duration and severity of disease. RESULTS: Bilirubin levels were significantly higher in PD patients than in controls (PD: 0.56 ±â€¯0.26 mg/dl, controls: 0.45 ±â€¯0.22 mg/dl; p < 0.001). In PD patients, we demonstrated a negative correlation between bilirubin levels and disease duration (p < 0.05). Higher bilirubin concentrations were identified in PD patients with Hoehn & Yahr stage ≤3. No relationship between bilirubin and treatment was found in PD patients. CONCLUSIONS: Increased bilirubin levels are particularly related to the first years of PD. Overexpression of oxidative enzymes could play an important role in PD etiology, leading to higher bilirubin levels in the early stages of PD.

Abnormal cerebellar connectivity and plasticity in isolated cervical dystonia.

There is increasing evidence that supports the role of the cerebellum in the pathophysiology of dystonia. We used transcranial magnetic stimulation to test the hypothesis that patients with cervical dystonia may have a disrupted cerebellar cortical connectivity at rest, and that cerebellar plasticity is altered too. We enrolled 12 patients with isolated cervical dystonia and 13 controls. A paired-pulse transcranial magnetic stimulation protocol was applied over the right cerebellum and the left primary motor area. Changes in the amplitude of motor evoked potentials were analysed. Continuous and intermittent Theta Burst Stimulation over the cerebellum was also applied. The effects of these repetitive protocols on cortical excitability, on intra-cortical circuits and on cerebellar cortical inhibition were analysed. In healthy subjects, but not in dystonic patients, a conditioning stimulus over the cerebellum was able to inhibit the amplitude of the motor evoked potentials from primary motor cortex. In healthy subjects continuous and intermittent cerebellar Theta Burst Stimulation were able to decrease and increase respectively motor cortex excitability. Continuous Theta Burst Stimulation was able to abolish the cerebellar cortical inhibition observed in basal condition. These effects were not observed in patients with cervical dystonia. Cerebellar cortical connectivity and cerebellar plasticity is altered at rest in patients with cervical dystonia.

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.

Lower levels of uric acid and striatal dopamine in non-tremor dominant Parkinson's disease subtype.

Parkinson's disease (PD) patients who present with tremor and maintain a predominance of tremor have a better prognosis. Similarly, PD patients with high levels of uric acid (UA), a natural neuroprotectant, have also a better disease course. Our aim was to investigate whether PD motor subtypes differ in their levels of UA, and if these differences correlate with the degree of dopamine transporter (DAT) availability. We included 75 PD patients from whom we collected information about their motor symptoms, DAT imaging and UA concentration levels. Based on the predominance of their motor symptoms, patients were classified into postural instability and gait disorder (PIGD, n = 36), intermediate (I, n = 22), and tremor-dominant (TD, n = 17) subtypes. The levels of UA and striatal DAT were compared across subtypes and the correlation between these two measures was also explored. We found that PIGD patients had lower levels of UA (3.7 vs 4.5 vs 5.3 mg/dL; P<0.001) and striatal DAT than patients with an intermediate or TD phenotype. Furthermore, UA levels significantly correlated with the levels of striatal DAT. We also observed that some PIGD (25%) and I (45%) patients had a predominance of tremor at disease onset. We speculate that UA might be involved in the maintenance of the less damaging TD phenotype and thus also in the conversion from TD to PIGD. Low levels of this natural antioxidant could lead to a major neuronal damage and therefore influence the conversion to a more severe motor phenotype.

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.

Long-term levodopa/carbidopa intestinal gel in advanced Parkinson's disease.

The short-term benefits of levodopa/carbidopa intestinal gel (LCIG) in patients with advanced Parkinson's disease (PD) are well documented, but the long-term benefits are still uncertain. The aim of this study was to investigate the motor and cognitive outcome of LCIG treatment in advanced PD after a follow-up period of at least 24 months. We assessed 29 patients with advanced PD who started LCIG infusion at our centre between 2007 and 2013. Motor fluctuations, parkinsonian symptoms, activities of daily living and impact on quality of life were evaluated. We also investigated the cognitive outcome using a battery of neuropsychological tests. All adverse events were recorded. Of the 29 PD patients who initiated LCIG, 16 patients reached the follow-up evaluation (24 months), after a mean time period of 32.2 ± 12.4 months. Six patients did not fulfil the 24-month follow-up visit and were evaluated after a mean time period of 8.6 ± 5.4 months. Seven patients discontinued the treatment before the scheduled visit. "Off" time and "On" dyskinesia duration were significantly reduced. LCIG improved quality of life and non motor symptoms, despite overall unchanged total levodopa doses prior to LCIG beginning. Motor and cognitive decline were detected. A relatively high number of adverse events occurred during the follow-up, above all, technical problems with the infusion device and mild problems related with gastrostomy. There were four cases of peripheral neuropathy (PN), 2 of which were considered serious. Our data confirm that LCIG is beneficial in the long-term treatment of advanced PD patients despite a decline in cognitive functions in a subgroup of patients, probably due to disease progression. PN in patients with LCIG may be more frequent than the published date suggest.

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.