The higher rate of MS preceding PD, albeit an uncommon occurrence, supports that MS may be part of the phenotypic spectrum of LRRK2 GS019S carriage, and provides further support for immune relation in LRRK2. The numerous, white matter lesions seen on neuropathology in one of the participants with MS and LRRK2 PD, and on MRI in the other, together with nigral cell loss in the first case, substantiate a chronic, demyelinating disorder separate from, and preceding, PD. The gene discussed is LRRK2; the disease is Parkinson disease.