For example, our results showed significant increase of CSF TNF-α concentration in patients with ALS, but a non-significant association between CSF TNF-α levels and AD (P = 0.095) or PD (p = 0.058), this phenomenon is likely because of the small number of studies included in the meta-analysis, and the high levels of heterogeneity among studies. This evidence concerns the gene TNF and amyotrophic lateral sclerosis.