Curiously, a recent study using α-synuclein seed amplification assay (SAA) on cerebrospinal fluid (CSF) from more than 1100 participants in the Parkinson’s Progression Marker Initiative (PPMI) cohort showed that SAA-positivity was significantly lower among LRRK2 PD than idiopathic PD patients [78]. This evidence concerns the gene LRRK2 and Parkinson disease.