Evaluation of causality between ADHD and Parkinson's disease: Mendelian randomization study

Area of Science:

• Neuroscience
• Genetics
• Psychiatry

Background:

• Attention-deficit hyperactivity disorder (ADHD) and Parkinson's disease (PD) have been anecdotally linked, with some studies suggesting psychostimulant use increases PD risk.
• The underlying relationship between ADHD and PD remains unclear, necessitating investigation into potential genetic correlations and causal associations.

Purpose of the Study:

• To investigate the genetic correlation and causal association between ADHD and PD using large-scale genome-wide association study summary statistics.
• To differentiate whether ADHD itself or psychostimulant treatment contributes to the observed increased risk of PD.

Main Methods:

• Utilized linkage disequilibrium score regression to assess genetic correlation between ADHD and PD.
• Employed Mendelian randomization analysis, specifically the inverse-variance weighted (IVW) method, with sensitivity analyses to evaluate causality.
• Analyzed summary statistics from large meta-analyses of ADHD (20,183 cases; 35,191 controls) and PD (26,421 cases; 442,271 controls).

Main Results:

• A weak, inverse genetic correlation was found between ADHD and PD (r=-0.100, P=0.026).
• Mendelian randomization analyses revealed no significant causal association between ADHD and PD in either direction, even after adjusting for BMI and smoking.
• A potential weak, inverse causal association of PD on ADHD was suggested but requires cautious interpretation.

Conclusions:

• This study provides strong evidence against a causal relationship between ADHD and PD.
• The observed positive association is likely attributable to unmeasured confounding factors.
• Future research should focus on the role of psychostimulant use in the risk of early-onset Parkinson's disease.