Liu FC, et al. - In this population-based family cohort study, researchers investigated familial aggregation and genetic contributions to Parkinson’s disease (PD) and the relative risks (RRs) of other neuropsychiatric diseases in relatives of PD patients. For this analysis, the records of all people actively registered in the Taiwan National Health Insurance Research Database in 2015 were queried (N=24,349,599). They identified 149,187 people with a PD-affected parent, 3,698 with an affected offspring, 3,495 with an affected sibling, and 15 with an affected twin. Results of this study suggested that first-degree relatives of PD patients were more likely to develop PD and other neuropsychiatric diseases. Environmental factors were found to account for a high proportion of the phenotypic variance of PD.