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Comment & Response
May 2017

Circulating Interleukin 6 in Parkinson Disease—Reply

Author Affiliations
  • 1Center on Translational Neuroscience, College of Life & Environmental Science, Minzu University of China, Beijing
JAMA Neurol. 2017;74(5):608. doi:10.1001/jamaneurol.2017.0040

In Reply We performed a random-effects meta-analysis with Comprehensive Meta-analysis Software, demonstrating elevated levels of the tumor necrosis factor, interleukin-1β (IL-1β), IL-2, IL-6, IL-10, C-reactive protein, and Regulated on Activation, Normal T-expressed, and Presumably Secreted among patients with Parkinson disease (PD) compared with healthy control participants.1 The calculation of between-study variance (τ2) in the Comprehensive Meta-analysis Software is the DerSimonian-Laird estimator, which, to our knowledge, is the most widely used model for random-effects meta-analysis. Although the 7 cytokines showed significant associations with PD, the statistical significance (Hedges g, 0.325; 95% CI, 0.007-0.643; P = .045) in blood IL-6 levels between patients with PD and healthy control participants is only slightly less than .05. Additionally, the sensitivity analysis, which tested the robustness of the outcome of the meta-analysis, suggested that unlike the tumor necrosis factor, a single study included in the meta-analysis could influence the significant association between IL-6 and PD.1 Therefore, when Nilsonne and Lekander performed a re-meta-analysis of the peripheral blood IL-6 levels in PD with a restricted maximum likelihood estimator, we were not surprised to see this model did not show a significant association between IL-6 and PD.

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