Table 3.
Systematic review of epidemiological literature for select traits of interest
| Factor | Study/studies (n) | Cases (n) | Controls (n) | OR | Lower limit of the OR 95% confidence interval | Upper limit of the OR 95% confidence interval | SE | P-value | I2 | Heterogeneity P-value |
|---|---|---|---|---|---|---|---|---|---|---|
| Ever versus never smokinga | 67 | 19 518 | 1 053 664 | 0.64 | 0.6 | 0.69 | 0.0347 | <0.001 | 49.60% | <0.001 |
| Drinking versus non-drinking coffeea | 19 | 5801 | 723 072 | 0.67 | 0.58 | 0.76 | 0.0684 | <0.001 | 42.90% | 0.025 |
| Hypertension preceding PDa | 12 | 5993 | 187 226 | 0.74 | 0.61 | 0.9 | 0.0989 | 0.003 | 76.50% | <0.001 |
| Diabetes preceding PDa | 13 | 20 025 | 303 543 | 0.91 | 0.72 | 1.15 | 0.1189 | 0.423 | 70.90% | <0.001 |
| Melanoma preceding PDb | 6 | – | – | 1.07 | 0.62 | 1.84 | – | – | 49.30% | 0.079 |
| Serum ironc | 10 | 520 | 711 | NS | NS | NS | – | – | 93.40% | <0.0000 |
| Bipolar disorder preceding PD | Shiba et al. (71, 83) | 196 | 196 | 1 | 0.1 | 16 | – | – | NA | NA |
| Psoriasis preceding PD | Rugbjerg et al. (72, 84) | 13 695 | 68 445 | 1.25 | 0.51 | 3.06 | – | – | NA | NA |
| Ulcerative colitis preceding PD | Rugbjerg et al. (72, 84) | 13 695 | 68 445 | 1.3 | 0.9 | 1.8 | – | – | NA | NA |
| Crohn's disease preceding PD | Rugbjerg et al. (72, 84) | 13 695 | 68 445 | 1.06 | 0.54 | 2.1 | – | – | NA | NA |
| Rheumatoid arthritis preceding PD | Rugbjerg et al. (72, 84) | 13 695 | 68 445 | 0.7 | 0.5 | 0.9 | – | – | NA | NA |
| Blood inflammatory markers preceding PDd | Chen et al. (73, 85) | 84 | 165 | 3.4 | 1.1 | 10.5 | – | – | NA | NA |
| Obesity preceding PDa | 3/7 studies described significant associations with obesity preceding PD through a variety of different measures (RR/OR 2.8f, 2.03f, 0.43f, 0.9, 0.8, 0.86, 0.99) | |||||||||
| Urate level preceding PDa | 3/5 studies described significant associations with elevated urate preceding PD using various cut-offs (ORs 0.4f, 0.6f, 0.71f, 0.43, 1.33) and 1 with preceding gout (OR 0.69f) | |||||||||
| Schizophrenia preceding PD$e | Two studies (Shiba et al. (71, 83): schizophrenia OR 1.0 (CI 0.1–7.0); Rajput et al. (74, 86): psychosis RR 1.5 (CI 0.3–6.7)) | |||||||||
| Serum amyloid | No known epidemiological studies comparing serum amyloid levels between PD and controls | |||||||||
NS, non-significant but figures not provided; NA, not available; RR, relative risk.
aSummary data from meta-analysis undertaken by Noyce et al. (1).
bSummary data from meta-analysis undertaken by Liu et al. (86). NB: After exclusion of the only negative study OR 1.44 (CI 1.06–1.96); association of existing PD with melanoma OR 3.61 (CI 1.49–8.77).
cSummary data from meta-analysis undertaken by Mariani et al. (87); data are for patients with established PD; Mariani et al. also report reduced transferrin and transferrin saturation.
dOR refers to highest quintile of IL-6 compared with the lowest (P for trend 0.03). Associations with high-sensitivity c-reactive protein (CRP), fibrinogen and tumor necrosis factor were non-significant. NB: In established PD, Song et al. (75, 87) reported increased high-sensitivity CRP compared with controls OR 2.04 (CI 1.18–3.52).
eRisk of bias through drug-induced parkinsonism due to neuroleptic treatment.
fStatistically significant result (where confidence interval not given).