SNCA and Parkinson disease: This contrasts with the often-stated stereotypic clinical picture of rapid progression and early dementia in patients with PD who are heterozygous for GBA1 mutations; it, moreover, suggests that the link between PD, Parkinson’s Disease Dementia (PDD) and its associated alpha-synuclein pathology is not simply related to the residual activity of lysosomal glucocerebrosidase.