# Causal association between phenylalanine and Parkinson’s disease: a two-sample bidirectional mendelian randomization study

## TL;DR

This study finds that phenylalanine may reduce the risk of Parkinson’s disease using genetic data and causal analysis.

## Contribution

The study provides novel causal evidence that phenylalanine is a protective factor for Parkinson’s disease.

## Key findings

- Phenylalanine was identified as a safety factor for Parkinson’s disease (p-value < 0.05, OR < 1).
- Reverse analysis found no causal link from Parkinson’s disease to phenylalanine (p-value > 0.05).
- Sensitivity tests confirmed the reliability of the Mendelian randomization results.

## Abstract

Research findings indicate a putative indirect or latent association between phenylalanine (Phe) and Parkinson’s disease (PD). In this study, we aimed to analyze the causal relationship between Phe and PD by two sample Mendelian randomization (MR) analysis.

In this study, the PD-related dataset and Phe-related dataset were downloaded from Integrative Epidemiology U1nit (IEU) Open Genome-Wide Association Study (GWAS) database. Four algorithms (MR Egger, maximum likelihood, inverse variance weighting (IVW) and unweighted regression) were used to perform MR analysis. The sensitivity analysis (heterogeneity test, horizontal pleiotropy test and Leave-One-Out (LOO) analysis) was used to assess the reliability of MR analyses.

In the forward MR analysis, Phe was a safety factor for PD (p-value < 0.05 and odds ratios (OR) < 1). The results of reverse MR analysis showed that there was no causal relationship between PD and Phe (p-value > 0.05). In addition, sensitivity analysis showed that MR analysis was reliable.

The results of this study revealed that Phe was a safety factor for PD, meaning that Phe reduced the risk of PD.