Work looking at the genetic basis of other PD-related features has been modest but has included age at onset, progression, comorbid features, pathologically defined PD, and modulation of penetrance and risk in individuals with mutations in either LRRK2 or GBA1. 6,7,69,70,71,72,73 In many instances, these studies have been hampered by limited data and small sample sizes; however, several associations have been revealed. Here, LRRK2 is linked to Parkinson disease.