A systematic review of associations between common SNCA variants and clinical heterogeneity in Parkinson's disease.

There is great heterogeneity in both the clinical presentation and rate of disease progression among patients with Parkinson's disease (PD). This can pose prognostic difficulties in a clinical setting, and a greater understanding of the risk factors that contribute to modify disease course is of clear importance for optimizing patient care and clinical trial design. Genetic variants in SNCA are an established risk factor for PD and are candidates to modify disease presentation and progression. This systematic review aimed to summarize all available primary research reporting the association of SNCA polymorphisms with features of PD. We systematically searched PubMed and Web of Science, from inception to 1 June 2020, for studies evaluating the association of common SNCA variants with age at onset (AAO) or any clinical feature attributed to PD in patients with idiopathic PD. Fifty-eight studies were included in the review that investigated the association between SNCA polymorphisms and a broad range of outcomes, including motor and cognitive impairment, sleep disorders, mental health, hyposmia, or AAO. The most reproducible findings were with the REP1 polymorphism or rs356219 and an earlier AAO, but no clear associations were identified with an SNCA polymorphism and any individual clinical outcome. The results of this comprehensive summary suggest that, while there is evidence that genetic variance in the SNCA region may have a small impact on clinical outcomes in PD, the mechanisms underlying the association of SNCA polymorphisms with PD risk may not be a major factor driving clinical heterogeneity in PD.

Validation and assessment of preanalytical factors of a fluorometric in vitro assay for glucocerebrosidase activity in human cerebrospinal fluid.

Lysosomal dysfunction is an emerging feature in the pathology of Parkinson's disease and Dementia with Lewy bodies. Mutations in the GBA gene, encoding the enzyme Glucocerebrosidase (GCase), have been identified as a genetic risk factor for these synucleinopathies. As a result, there has been a growing interest in the involvement of GCase in these diseases. This GCase activity assay is based on the catalytic hydrolysis of 4-methylumbelliferyl ß-D-glucopyranoside that releases the highly fluorescent 4-methylumbelliferyl (4-MU). The final assay protocol was tested for the following parameters: Lower limit of quantification (LLOQ), precision, parallelism, linearity, spike recovery, number of freeze-thaw events, and sample handling stability. The GCase activity assay is within acceptable criteria for parallelism, precision and spike recovery. The LLOQ of this assay corresponds to an enzymatic activity of generating 0.26 pmol 4-MU/min/ml. The enzymatic activity was stable when samples were processed and frozen at - 80 °C within 4 h after the lumbar puncture procedure. Repetitive freeze-thaw events significantly decreased enzyme activity. We present the validation of an optimized in vitro GCase activity assay, based on commercially available components, to quantify its enzymatic activity in human cerebrospinal fluid and the assessment of preanalytical factors.

Evolution of cerebrospinal fluid total α-synuclein in Parkinson's disease.

INTRODUCTION: Cerebrospinal fluid (CSF) total α-synuclein is considered a potential biomarker for Parkinson's disease (PD), but little is known about the evolution of this marker during the course of the disease. Our objective was to investigate whether CSF total α-synuclein concentrations change over time and are associated with motor and cognitive function in PD. METHODS: CSF total α-synuclein concentrations were quantified in 56 longitudinally followed PD patients, 27 of whom provided CSF repeatedly 2 and/or 4 years later. Another 18 subjects were included as controls. The samples were analyzed using two independent, validated ELISA methods: our recently developed and validated in-house ELISA and a commercial kit from BioLegend. RESULTS: CSF total α-synuclein levels did not distinguish PD patients from controls, displayed no substantial changes during a period of up to 4 years, and did not predict subsequent motor or cognitive decline. These findings were consistent for both analytical methods. CONCLUSION: Our findings do not support the clinical utility of total α-synuclein as a single diagnostic or prognostic biomarker in PD.

Validation of a new assay for α-synuclein detection in cerebrospinal fluid.

BACKGROUND: Abnormal α-synuclein aggregation and deposition is the pathological hallmark of Parkinson's disease (PD) and dementia with Lewy bodies (DLB), but is also found in Alzheimer disease (AD). Therefore, there is a gaining interest in α-synuclein in cerebrospinal fluid (CSF) as potential biomarker for these neurodegenerative diseases. To broaden the available choices of α-synuclein measurement in CSF, we developed and validated a new assay for detecting total α-synuclein. METHODS: This novel ELISA uses commercially available antibodies and is based on electrochemiluminescence technology. The assay protocol is straightforward, with short and simple incubation steps, and requires only small amounts of CSF. We validated this assay for precision, parallelism, dilution linearity, specificity, and spike recovery. We further compared it to the newly validated α-synuclein assay from BioLegend by analyzing a set of 50 CSF samples with both assays. RESULTS: The new assay quantifies α-synuclein in CSF with a lower limit of detection of 36.3 pg/mL and shows no cross-reactivity with human ß- and γ-synuclein. Results of dilution linearity, parallelism, spike recovery, and precision classify this assay as well suited for α-synuclein detection in human CSF samples. CONCLUSIONS: We present a novel assay based on freely available components to quantify total α-synuclein in CSF as an additional method for α-synuclein as a biomarker in neurodegenerative diseases. The assay convinces with its simple and convenient protocol paired with high sensitivity.