There are indications that GRN mutations may play a role in other neurodegenerative diseases, such as amyotrophic lateral sclerosis (55), Parkinson’s disease (56), and AD (57–61), with increased PGRN levels having been shown to inhibit plaque formation and protect against amyloid beta toxicity in mouse models of AD (62, 63). This evidence concerns the gene GRN and Parkinson disease.