LRRK2 and Parkinson disease: Ideally, subjects at risk, such as carriers of specific mutations in the glucosylceramidase beta 1 (GBA1) or LRRK2 genes or subjects with prodromal symptoms such as rapid eye movement (REM) sleep without atonia or decreased sense of smell, could undergo a simple procedure to extract a skin biopsy, undergo full SRM aggregate analysis, and potentially be treated (if positively diagnosed with the pathological biomarker for PD) before irreversible neural damage has occurred.