Does genetic testing remain relevant in advanced Parkinson's disease?

Genetic testing is traditionally emphasized in early-onset or familial Parkinson's disease (PD), leaving its role in advanced disease uncertain. This mini-review explores, from the perspectives of patients, their family members, and clinical researchers, whether genetic investigation remains meaningful once patients reach advanced PD. In large prospective clinical-genetic screening cohorts, roughly one in seven PD patients has genetic PD. Established genotype-phenotype correlations, spanning cognitive trajectory, levodopa responsiveness, and deep brain stimulation outcomes, continue to inform clinical decision-making even at advanced stages. Thus, patients may gain psychological clarity, receive refined prognostic counseling, and become eligible for gene-specific trials or registries. In addition, patients express altruistic motivations, considering the merit of sharing their genetic testing results with their families and the research community. Unaffected relatives may benefit from more precise, penetrance-informed risk assessment, appropriately scaled surveillance, lifestyle counseling, and reproductive planning, particularly as potential environmental modifiers of penetrance and age at onset become better characterized. Researchers rely on genetically characterized advanced-stage cohorts to identify genotype-phenotype relations, modifiers of onset, progression and treatment response, validate biomarkers, and build the large, deep longitudinal datasets required for emerging gene- and pathway-targeted therapies. Collectively, these perspectives argue against a narrow early-disease "window of opportunity" for genetic testing in PD. Rather than becoming obsolete once the disease reaches a more advanced stage, genetic characterization continues to shape individualized care, family counseling, and translational research. Thus, in the future, the challenge should no longer be to justify genetic testing in advanced PD, but to embed it equitably and systematically within standard care and international research infrastructure across the entire disease course.