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.

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.

Aberrant cortical associative plasticity associated with severe adult Tourette syndrome.

BACKGROUND: Recent studies have shown altered cortical plasticity in adult patients with Tourette syndrome. However, the clinical significance of this finding remains elusive. METHODS: Motor cortical plasticity was evaluated in 15 adult patients with severe Tourette syndrome and 16 healthy controls using the paired associative stimulation protocol by transcranial magnetic stimulation. Associations between paired associative stimulation-induced plasticity and relevant clinical variables, including cortical excitability, psychiatric comorbidities, drug treatment and tic severity, were assessed. RESULTS: Motor cortical plasticity was abnormally increased in patients with Tourette syndrome compared with healthy subjects. This abnormal plasticity was independently associated with tic severity. CONCLUSION: Patients with severe Tourette syndrome display abnormally increased cortical associative plasticity. This aberrant cortical plasticity was associated with tic severity, suggesting an underlying mechanism for tic pathophysiology.

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.

Effects of two weeks of cerebellar theta burst stimulation in cervical dystonia patients.

Dystonia is generally regarded as a disorder of the basal ganglia and their efferent connections to the thalamus and brainstem, but an important role of cerebellar-thalamo-cortical (CTC) circuits in the pathophysiology of dystonia has been invoked. Here in a sham controlled trial, we tested the effects of two-weeks of cerebellar continuous theta burst stimulation (cTBS) in a sample of cervical dystonia (CD) patients. Clinical evaluations were performed by administering the Toronto Western Spasmodic Torticollis Rating Scale (TWSTRS) and the Burke-Fahn-Marsden Dystonia Rating Scale (BFMDRS). We used TMS to measure the inhibitory connectivity between the cerebellum and the contralateral motor cortex (cerebellar brain inhibition [CBI]), and the excitability of the contralateral primary motor cortex assessing intracortical inhibition (SICI), intracortical facilitation (ICF) and cortical silent period (CSP). Paired associative stimulation (PAS) was tested to evaluate the level and the topographical specificity of cortical plasticity, which is abnormally enhanced and non-focal in CD patients. Two weeks of cerebellar stimulation resulted in a small but significant clinical improvement as measured by the TWSTRS of approximately 15%. Cerebellar stimulation modified the CBI circuits and reduced the heterotopic PAS potentiation, leading to a normal pattern of topographic specific induced plasticity. These data provide novel evidence CTC circuits could be a potential target to partially control some dystonic symptoms in patients with cervical dystonia.

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.

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.

PSMC1 Gene in Parkinson's Disease.

BACKGROUND: Impairment of the ubiquitin-proteasome system has been suggested to play an important role in the pathogenesis of Parkinson's disease (PD). The 26S proteasome regulatory subunit 1 is encoded by the gene PSMC1 in humans. PSMC1 knockout mice showed a PD-like phenotype. Our aim was to analyze the association between variations in this gene and the susceptibility to develop PD. METHODS: We included 283 PD patients (165 males and 118 females) with a mean age of 63.6±11.2 years (mean age at onset 55.4±12.7 years), and 316 unrelated control subjects (193 males and 123 females) with a mean age of 61.5±12.3 years. Four polymorphisms, providing haplotype information of PSMC1, were genotyped using TaqMan assays. Moreover, in order to identify new variations, all exons of the PSMC1 gene and their exon-intron boundaries were analyzed using high-resolution melting analysis. RESULTS: Minor allele frequencies in PD patients and control subjects were similar. The gene coding sequence analysis showed no variation associated with the disease either. CONCLUSIONS: Our results suggest that there is no association between variations or haplotypes in the PSMC1 gene and PD, indicating that this gene is probably not involved in the pathogenesis of PD.

Intermediate alleles at the FRAXA and FRAXE loci in Parkinson's disease.

BACKGROUND: It is debatable whether the size of triplet repeats of the fragile X mental retardation genes FMR1 and FMR2 (found at the FRAXA and FRAXE loci) is associated with Parkinson's disease (PD). The aims of the current study were to investigate the relationship between these genes and PD and to determine whether these genes affected clinical manifestations of PD. METHODS: We recruited 206 PD patients and 227 control subjects from southern Spain. All subjects were screened for the size of CGG and CCG repeats at the FRAXA and FRAXE loci, respectively. Clinical features of each patient were examined in detail to study possible association between these features and genotype. RESULTS: Frequencies of FRAXA and FRAXE intermediate alleles were similar between PD and control groups. Clinical characteristics in PD patients, including severity of the disease, motor and non-motor symptoms, and motor complications and fluctuations were not affected by intermediate alleles at either locus. Two patients carrying FRAXA premutation alleles were identified showing clinical manifestations indistinguishable from idiopathic PD. CONCLUSIONS: FRAXA and FRAXE intermediate alleles do not seem to affect the risk for PD or modify clinical features in PD patients.