title: Parkinson's disease in twins: a follow-up study.
abstract: OBJECTIVE
  To reevaluate concordance rates in 9 monozygotic (MZ) and 12 dizygotic (DZ) twin pairs with PD 8 years after the initial study.
  
  
  BACKGROUND
  Longitudinal investigations increase accuracy in clinical diagnosis of PD.
  
  
  METHODS
  Follow-up by personal interview and clinical examination.
  
  
  RESULTS
  Concordance rates were not different between MZ (3/9) and DZ (5/12) twin pairs at follow-up, even when PD-associated dementia and isolated postural tremor were considered diagnostic of familial Lewy body parkinsonism. Evaluation of medical history, personality traits, and blink rate did not reveal putative early or premorbid parkinsonism in 9 co-twins who were motor-asymptomatic during the follow-up interval. However, these co-twins had reduced semantic fluency in comparison with a healthy control group of similar age. None of 7 co-twins without motor signs who underwent PET investigation 6 years previously showed signs of extrapyramidal disease at follow-up, but verbal memory continued to be reduced in 5 of these co-twins.
  
  
  CONCLUSIONS
  Based on concordance rates only, the findings in our twin sample do not support a major genetic impact for the motor expression of PD.
authors.affiliation: Department of Neurology, Medical University, Lübeck, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Vieregge
authors.forename: J
authors.initials: J
authors.lastname: Hagenah
authors.forename: I
authors.initials: I
authors.lastname: Heberlein
authors.forename: C
authors.initials: C
authors.lastname: Klein
authors.forename: H P
authors.initials: HP
authors.lastname: Ludin
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001921:Brain / Q000000981:diagnostic imaging; D004200:Diseases in Twins; D005260:Female; D005500:Follow-Up Studies; D006801:Humans; D008297:Male; D008875:Middle Aged; D010300:Parkinson Disease / Q000000981:diagnostic imaging / Q000503:physiopathology*; D013997:Time Factors; D014055:Tomography, Emission-Computed