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Plasma alpha-synuclein levels in patients with Parkinson’s disease: a systematic review and meta-analysis

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Abstract

Objective

To date, there are no definitive biomarkers for diagnose Parkinson’s disease (PD). The detection of α-synuclein (α-Syn) in plasma of PD patients has yielded promising but inconclusive results. To determine the performance of α-Syn as a diagnostic biomarker of PD, we used a meta-analysis.

Methods

We identified 173 studies through a systematic literature review. From those, only studies reporting data on total α-Syn levels were included in the meta-analysis (10 publications, 1302 participants). Quality of studies was assessed by Newcastle-Ottawa scale.

Results

The α-Syn levels were significantly higher in PD patients than healthy controls (standardized mean difference [SMD] = 0.778, 95% confidence interval = 0.284 to 1.272, p = 0.002). Similar results were found after omitting any individual study from meta-analysis, with SMD ranges from 0.318 (95% CI = 0.064 to 0.572, p = 0.014) to 0.914 (95% CI = 0.349 to 1.480, p = 0.002). According to meta-regression analysis, increased mean patients age (slope = − 0.232, 95% CI = − 0.456 to − 0.008, p = 0.042), increased total number of participants (slope = − 0.007, 95% CI = − 0.013 to − 0.0004, p = 0.038), and increased percentage of males (slope = − 6.444, 95% CI = − 10.841 to − 2.047, p = 0.004) were associated with decreased SMD of α-Syn levels across studies. We did not find any significant association between the SMD in α-Syn levels and disease duration, disease severity, and quality of studies. Most of studies applied ELISA assays.

Conclusion

Total plasma α-Syn levels were higher in PD patients than controls. Analytical factors were important limitations.

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Abbreviations

α-Syn:

α-Synuclein

CI:

Confidence interval

CSF:

Cerebrospinal fluid

ELISA:

Enzyme-link immunosorbent assay

H&Y scale:

Hoehn and Yahr scale

I2 :

I-squared

NOS:

New Castle-Ottawa scale

PD:

Parkinson’s disease

PRISMA:

Preferred reporting items for systematic reviews and meta-analyses

RBCs:

Red blood cells

SMD:

Standardized mean difference

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Authors and Affiliations

  1. Neurochemistry laboratory, 1st Department of Neurology and Movement Disorders, Medical School, Aeginition Hospital, National and Kapodistrian University of Athens, 72-74 Vasilissis Sofias Avenue, 11528, Athens, Greece

    Anastasia Bougea, George P Paraskevas & Elisabeth Kapaki

  2. Neuroscience laboratory, Center for Basic Research, Biomedical Research Foundation of the Academy of Athens, Athens, Greece

    Anastasia Bougea, Leonidas Stefanis, Evangelia Emmanouilidou & Kostas Vekrelis

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  1. Anastasia Bougea
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  2. Leonidas Stefanis
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Bougea, A., Stefanis, L., Paraskevas, G.P. et al. Plasma alpha-synuclein levels in patients with Parkinson’s disease: a systematic review and meta-analysis. Neurol Sci 40, 929–938 (2019). https://doi.org/10.1007/s10072-019-03738-1

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