SNCA and Parkinson disease: Of the six documented familial PD mutations in SNCA (A30P, E46K, H50Q, G51D, A53E, and A53T) (13, , , , –18), the G51D mutation causes the earliest onset, even in the 10 y, with an aggressive course that includes dementia and resembles multiple system atrophy (MSA), another Synucleinopathy (15, 17, 19).