The demonstration of MJFR14-6-4-2 proximity ligation assay positive aggregates in brains affected by Parkinson's disease and LRRK2 mutations, motivated the analysis of α-synuclein oligomers in brain cytosol from dementia with Lewy bodies (DLB) and control cases by combining size-exclusion chromatography, aggregate-specific MJFR14-6-4-2 ELISA and SDS-denaturing immunoblotting. This evidence concerns the gene LRRK2 and Parkinson disease.