LRRK2 and Parkinson disease: Unexpectedly, LRRK2-PD patients (mean ± SEM = 24,510 ± 7,161, n = 13) did not show any significant difference in the level of o-α-syn in the CSF relative to the healthy control group (P = 0.1910, Mann-Whitney U test), possibly because of the low number of individuals in this group (n = 13 vs. n = 42).