Familial aggregation of Parkinson's disease may affect progression of motor symptoms and dementia

Background Familial aggregation has been described in PD of both early and late onset, but has not been studied in a true population‐based sample. Moreover, little is known about its association with disease progression and endophenotypes. Objectives The objectives of this work were to determine familial aggregation of idiopathic PD in a population‐based cohort and study the association with clinical endophenotypes and disease progression. Methods We examined family history data from the Norwegian ParkWest study, a well‐characterized, population‐based cohort of incident PD patients and age‐matched healthy controls. Family data were collected at baseline with a simplified questionnaire (192 cases and 193 controls) and after 3 years of longitudinal follow‐up using an extended questionnaire (172 cases and 171 controls). Results Compared to the controls, the PD patients had an increased relative risk of having a first‐degree relative with PD when using the extended questionnaire (relative risk = 1.988; P = 0.036), but not when using the simplified questionnaire (relative risk = 1.453; P = 0.224). There was no significant difference in age of onset or motor subtype ( P = 0.801). However, cases with a family history of PD had reduced progression over 7 years as measured by UPDRS II ( P = 0.008) and smaller rate of decrease of MMSE ( P = 0.046). Conclusions Our findings confirm familial aggregation in a population‐based cohort of idiopathic PD. Moreover, we show that positive family history of PD in patients is associated with a slower progression of PD symptoms and cognitive decline. © 2016 International Parkinson and Movement Disorder Society