TABLE 1.
The detailed characteristics of each included study
| Author | Year of publication | Study site | Type of study | Number of patients | Method | Mean age | Sex ratio | Duration of PD | Alpha‐synuclein(total) | Alpha‐synuclein(oligo) | Alpha‐synuclein (Oligo/total) | ||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| PD | HC | PD | HC | PD (F/M) | HC (F/M) | PD | HC | PD | HC | PD | HC | ||||||
| Al‐Nimer | 2014 | Iraq | CS | 20 | 20 | ELISA | 64.4 (10.6), 66 | 65.4 (8.2), 64 | 4/16 (25%) | 2/18 (11.11%) | 6.55 ± −6.83 (4) | 65 ± 52.2 pg/ml | 314.01 ± 435.9 | NA | NA | ||
| Cao | 2018 | China | CS | 74 | 60 | ECL (Electro chemiluminescence) | 59.62 (8.57) | 58.75 (9.85) | 34/40 (85%) | 34/26 (130.77%) | 5.5 (3–7.5) | 11.39 (6.23–28.11) | 12.23 (5.47–58.83) | 10.39 ± 1.46 (pg/ng) | 1.37 ± 0.24 | 1.70 ± 0.52(pg/ng) | 0.67 ± 0.26 |
| Devic | 2011 | USA | CS | 24 | 25 | Luminex | 63.5 (11.3) | 58 (10.4) | 7/17 (41.2%) | 14/11 (127.3%) | 8.5 (6.4) | 70 ± 80 pg/ml | 110 ± 130 | NA | NA | ||
| Goldman | 2018 | USA | CS | 115 | 88 | ELISA | 68.24 (6.40) | 65.64 (7.36) | 43/72 (59.7%) | 29/59 (49.2%) | 8.34 (3.09) | 285.42 ± 400.13 pg/ml | 165.97 ± 272.15 | NA | NA | ||
| Kang | 2016 | China | CS | 201 | 67 | Luminex | 63.18 (9.67) | 61.04 (10.01) | 79/122 (64.75%) | 26/41 (63.41%) | NA | 128.66 ± 98.2 pg/ml | 131.31 ± 104.1 | ||||
| Shaheen | 2020 | Egypt | CS | 25 | 15 | ELISA | 60.1 (5.6) | 60 ± 6.7 | 10/15 (66.67%) | 5/10 (50%) | 3.8 ± 2.7 | 159.4 ± 61.6 ng/ml | 229.9 ± 64 | 47.8 ± 11.8ng/ml | 39.2 ± 9.2 | 0.35 ± 0.18 | 0.19 ± 0.08 |
| Stewart | 2014 | USA | CS | 24 | 198 | Luminex | 63.5 ± 11.3 | 54.9 | 7/17 (41.18%) | 61/137 (44.53%) | 8.4 (6.4) | 0.07 ± 0.08 (NA) | 0.37 ± 0.02 pg/miug | NA | NA | ||
| Vivacqua | 2016 | Italy | CS | 60 | 40 | ELISA | 66.3 (8.78) | 68.3 (7.9) | 29/31 (93.55%) | 18/22 (81.82%) | 6.7 (10.4) | 5.08 ± 3.01 pg/ml | 31.3 ± 22.4 | 1.062 ± 0.266 ng/ml | 0.498 ± 0.203 | 0.174 ± 0.044 | 0.065 ± 0.027. |
| Vivacqua | 2019 | Italy | CS | 112 | 90 | ELISA | 69.01 (11.16) | 62.09 (15.08) | 53/59 (89.83%) | 37/53 (69.81%) | NA | 7.104 ± 5.122 pg/ml | 28.444 ± 25.877 | 0.893 ± 1.949 ng/ml | 0.217 ± 0.191 | 0.235 ± 0.793 | 0.013 ± 0.008 |
| Lufen Su | 2018 | China | CS | 27 | 27 | ELISA | 61.52 (9.57) | 58.37 (10.63) | 12/15 (80%) | 12/15 (80%) | NA | 1269.02 ± 16.09 ng/ml | 1350.51 ± 25.79 | NA | NA | NA | NA |
| Fernandez‐Espejo | 2021 | Spain | CS | 45 | 30 | ELISA | 61.4 (18.5) | 59.6 (11) | 18/27 (66.67%) | 18/12 (150%) | 9.9 ± 6.8 | 361.9 ± 89 pg/ml | 372.1 ± 91 | ||||
| Kawabe | 2013 | Japan | CS | 20 | 20 | Restriction Enzyme Analysis | NA | NA | NA | NA | NA | 78.9 ± 91.9 pg/ml | 158.1 ± 71.7 | ||||
| Pang | 2016 | China | CS | 38 | 21 | Enzymatic cholorimetry | 68.3 (10.6) | 60.5 (11.4) | 17/21 (80.95%) | 12/9 (133.3%) | NA | 1.35 ± 9.87 U/L | 1.63 ± 1.21 | ||||
Abbreviations: CS, Cross‐sectional; ELISA, enzyme‐linked immunosorbent assay; HC, Healthy controls; PD, Parkinson disease.