Laura Vargas-González

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.

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

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.

Analysis of c.801-2A>G mutation in the DNAJC6 gene in Parkinson's disease in southern Spain.

Recently, a new mutation has been described in the DNAJC6 gene, the c.801-2A>G, as involved in an autosomal-recessive juvenile parkinsonism [1]. DNAJC6 gene, located in the 1p31.1 chromosome, encodes a protein called auxilin-1, which is selectively expressed in neurons. This protein confers specificity to the ATPase activity of its partner Hcs70 in clathrin uncoating, acting in the intracellular endocytosis pathway and vesicle recycling. Its malfunction leads to impaired synaptic vesicle recycling and disturbed clathrin mediated endocytosis (CME). Since dopamine receptors are internalized by CME to be degraded by the endosomal system, mutations in DNAJC6 may lead to an abnormal dopamine receptor metabolism and thereby associated parkinsonism [2]. Our aim was to study the presence of the mutation c.801-2A>G in DNAJC6 gene in a cohort of PD patients from southern Spain. The study was approved by the ethic committee of the Hospital Universitario Virgen del Rocío. The participating subjects provided written informed consent. A total of 356 PD patients (54.8% males and 45.2% females; mean age 63.55 11.63 years; mean age at onset 55.13 13.2 years) and 424 healthy control subjects (51.4% males and 48.6% females; mean age 60.87 12.44 years) were included. Fifty-six PD patients were familial PD. Twenty-one patients displayed a juvenile-onset PD (JOPD; <35 years old) and thirty-six an early-onset PD (EOPD; between 35 and 45 years old). We used several methods to study the DNAJC6 mutation c.8012A>G in our population. Firstly a SimpleProbe assay was designed complementary to the mutated sequence in order to detect the presence of the mutation c.801-2A>G. Annealing of the probe to wild type and mutant sequences and subsequent melting analysis results in different melting temperatures (Tm). The LightCycler480 software Tm calling and genotyping analysis modules were used to analyze the SimpleProbe melting curve data and we did not detect the analyzedmutation. This is a very specific technique but we have no positive sample as a control. Therefore, we performed a HRM analysis as a complementary technique, and we did not find the mutation c.801-2A>G. However, a previously described polymorphism (rs146050826; p.Ala220Thr) was found in two control subjects, who were 57 and 74 years old, both without any specific clinical manifestation. HRM analysis also has limitations because it can sometimes be difficult to discriminate between homozygous wild-type and homozygous mutant samples. Therefore, as an additional control, we generated a mutated control fragment by mismatched PCR and re-analyzed 25% of our samples by a new HRM analysis, and the results did not change. These techniques are believed to produce valid results.

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 Parkinsons 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.

Lack of Validation of Variants Associated With Cervical Dystonia Risk: A GWAS Replication Study

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.

Low serum uric acid levels in progressive supranuclear palsy

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.

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.

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.

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

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.

Genetic analysis of CHCHD2 in a southern Spanish population

Researching genetic factors involved in Parkinsons 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.