title: Familial aggregation of Parkinson's disease may affect progression of motor symptoms and dementia.
abstract: 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.
  
  
  
  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.
  
  
  
  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).
  
  
  
  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).
  
  
  
  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.
authors.affiliation: Department of Neurology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Johannes Jernqvist
authors.initials: JJ
authors.lastname: Gaare
authors.affiliation: Department of Neurology, Haukeland University Hospital, Bergen, Norway.
authors.forename: Geir Olve
authors.initials: GO
authors.lastname: Skeie
authors.affiliation: Department of Neurology, Haukeland University Hospital, Bergen, Norway.|Department of Clinical Medicine, University of Bergen, Bergen, Norway.
authors.forename: Charalampos
authors.initials: C
authors.lastname: Tzoulis
authors.affiliation: Network for Medical Sciences, University of Stavanger, Stavanger, Norway.
authors.forename: Jan Petter
authors.initials: JP
authors.lastname: Larsen
authors.affiliation: Department of Neurology, Haukeland University Hospital, Bergen, Norway.|Department of Clinical Medicine, University of Bergen, Bergen, Norway.
authors.forename: Ole-Bjørn
authors.initials: OB
authors.lastname: Tysnes
mesh_terms: D017668:Age of Onset; D000368:Aged; D003704:Dementia / Q000453:epidemiology* / Q000209:etiology; D018450:Disease Progression; D058068:Endophenotypes; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D000073216:Mental Status and Dementia Tests; D008875:Middle Aged; D009664:Norway / Q000453:epidemiology; D010300:Parkinson Disease / Q000150:complications / Q000453:epidemiology*; D010375:Pedigree; D012720:Severity of Illness Index
keywords: Parkinson's disease; disease characteristics; familial aggregation; family history; first-degree relatives; genetics; prospective cohort