A mutation long associated with Parkinson's disease may have persisted in human populations partly because it confers a meaningful advantage against bacterial infection — a classic evolutionary trade-off that reshapes how we think about neurodegenerative disease genetics. Understanding why disease-linked genes endure is a central puzzle in medicine, and this research offers a compelling mechanistic answer for one of the most studied Parkinson's-associated variants.
The G2019S variant of LRRK2, which elevates the kinase's enzymatic activity, was found to enhance bacterial killing by neutrophils through a specific molecular cascade. In mouse models infected with Salmonella typhimurium and Listeria monocytogenes, the mutation promoted phosphorylation of the p40phox and p47phox cytosolic subunits of the NADPH oxidase-2 (NOX2) complex, triggering their translocation to lysosomes — the cellular compartments responsible for digesting pathogens. This repositioning amplified oxidative burst activity, dramatically improving bacterial clearance. The effect was partly counteracted by the Salmonella virulence factor SifA, which redirects bacterial compartments away from lysosomes; when SifA was deleted, the G2019S advantage became even more pronounced. Notably, other immune signaling molecules — Cathepsin B, Rab10, and PKC — were uninvolved in this pathway.
This finding fits within a growing literature on evolutionary antagonistic pleiotropy — the idea that alleles causing late-life disease may have been retained because they enhanced survival during infectious disease pressure earlier in life. LRRK2 variants have already been linked to susceptibility to Crohn's disease and leprosy, suggesting the gene sits at a critical immune-pathogen interface. The core limitation here is the reliance on murine infection models, which do not perfectly replicate human neutrophil biology or LRRK2 expression dynamics. The proposed mechanism — that superior NOX2-driven pathogen control generates chronic oxidative tissue damage that ultimately contributes to neurodegeneration — is plausible but remains inferential. If validated in human cells and longitudinal cohorts, this work could reframe LRRK2 inhibition strategies in Parkinson's therapy, requiring careful consideration of infectious disease vulnerability as a therapeutic side effect.