The study reported mixed findings, with effects ranging from neutral to potentially adverse in the context of the smoking-PD association, depending on the specific SV2C genotype, suggesting that smoking’s or nicotine’s efficacy as a neuroprotective treatment may differ among individuals, so only a subset of the population will benefit from nicotine as a protective measure against PD [26]. The gene discussed is SV2C; the disease is Parkinson disease.