CSF N-acylethanolamine acid amidase level and Parkinson's disease risk: A mendelian randomization study

Neuroinflammation is involved in the progression of Parkinson's disease (PD), and N-acylethanolamine acid amidase (NAAA) is involved in regulating inflammation by hydrolyzing bioactive lipid mediators called N-acylethanolamines (NAEs). However, the causal relationship between cerebrospinal fluid (CSF) NAAA protein levels and the risk of PD remains unclear. This study aimed to explore the causal effect of CSF NAAA levels on PD risk through Mendelian randomization (MR) analysis.

Genome-wide association study (GWAS) summary statistics for CSF NAAA protein quantitative trait loci (pQTL) and GWAS summary statistics for PD were obtained from publicly available databases. Inverse-variance weighted (IVW) was the main causal estimation method for MR analysis. In addition, the maximum likelihood, MR Egger regression, and weighted median were used to supplement the IVW results. Finally, various sensitivity tests were performed to verify the reliability of the MR findings.

In the initial MR analysis, the IVW showed that CSF NAAA protein levels significantly increased PD risk (odds ratio [OR] = 1.17, 95% confidence interval [CI]: 1.01-1.35, P = 0.031). This finding was further validated in a replicate MR analysis (OR = 1.20, 95% CI: 1.02-1.41, P = 0.027). Sensitivity analysis showed that MR results were stable and not affected by heterogeneity and horizontal pleiotropy.

The present MR study supports a causal relationship between elevated CSF NAAA protein levels and increased PD risk.