At risk populations, such as individuals with mutations in the leucine-rich repeat kinase2 (LRRK2) and glucosylceramidase β1 (GBA1) genes6,7, patients with rapid eye movement sleep behavior disorder (RBD)8 or hyposmia with dopamine transporter deficits9, are ideal populations to examine neurodegeneration in the prodromal phase of PD since RBD10,11 and hyposmic12 patients have a high risk of phenoconverting to PD or other synucleinopathies. The gene discussed is GBA1; the disease is REM sleep behavior disorder.