Relationship between smoking and ALS: Mendelian randomisation interrogation of causality

Area of Science:

• Neuroscience
• Genetics
• Epidemiology

Background:

• Smoking is a known risk factor for many diseases, but its link to amyotrophic lateral sclerosis (ALS) remains debated.
• Previous studies on smoking and ALS are conflicting and potentially biased by confounding factors.

Purpose of the Study:

• To investigate the causal relationship between smoking and amyotrophic lateral sclerosis (ALS) using robust genetic methods.
• To reduce confounding bias inherent in observational studies by employing Mendelian randomization.

Main Methods:

• Utilized large-scale genome-wide association studies (GWAS) data for smoking phenotypes (lifetime and ever smoking) and ALS.
• Applied Mendelian randomization (MR) techniques, including inverse variance weighted (IVW) and other MR methods, to assess causality.
• Conducted bidirectional analyses to explore potential reverse causality between smoking and ALS.

Main Results:

• No significant evidence of a causal link was found between lifetime smoking and ALS (OR 0.94, p=0.59) or ever smoking and ALS (OR 1.10, p=0.05) using the IVW MR method.
• Bidirectional analyses also did not support a causal or reverse causal relationship.

Conclusions:

• Mendelian randomization analyses using large genetic datasets do not support smoking as a causal factor for amyotrophic lateral sclerosis (ALS).
• Future research could explore other smoking phenotypes, such as current smoking, using similar genetic epidemiology approaches.