title: Smell identification ability in twin pairs discordant for Parkinson's disease.
abstract: Olfactory dysfunction has been proposed to be a sign that may precede the motor features of Parkinson's disease (PD). To determine whether smell identification deficits predict subsequent PD, we studied smell identification ability using the University of Pennsylvania Smell Identification Test (UPSIT) in 62 members of male twin pairs discordant for PD at baseline. Smell identification ability was reduced at baseline in the twins with PD compared to their unaffected brothers (23 vs. 31 of 40; P = 0.001). UPSIT scores were not reduced in the twins without PD when compared to age- and gender-specific normal values. After a mean interval of 7.3 years, 28 unaffected twins were still alive and 19 agreed to a second evaluation. Two had newly developed PD. Neither twin had impaired smell identification at baseline. The average decline in UPSIT percentile scores in these 2 twins was greater than in the 17 twins who did not develop PD (-68% vs. -24%; P = 0.01). In subjects who did not meet Core Assessment Program for Intracerebral Transplantations diagnostic criteria for PD at baseline, the presence of cardinal signs of parkinsonism was not associated with lower baseline UPSIT scores nor with a subsequent decline. Smell identification ability may not be a sensitive indicator of future PD 7 or more years before the development of motor signs, even in a theoretically at-risk population.
authors.affiliation: The Parkinson's Institute, Sunnyvale, California, USA. connie.marras@utoronto.ca
authors.forename: Connie
authors.initials: C
authors.lastname: Marras
authors.forename: Samuel
authors.initials: S
authors.lastname: Goldman
authors.forename: Amanda
authors.initials: A
authors.lastname: Smith
authors.forename: Peter
authors.initials: P
authors.lastname: Barney
authors.forename: Diana
authors.initials: D
authors.lastname: Aston
authors.forename: Kathleen
authors.initials: K
authors.lastname: Comyns
authors.forename: Monica
authors.initials: M
authors.lastname: Korell
authors.forename: J William
authors.initials: JW
authors.lastname: Langston
authors.forename: G Webster
authors.initials: GW
authors.lastname: Ross
authors.forename: Caroline M
authors.initials: CM
authors.lastname: Tanner
mesh_terms: D000368:Aged; D016022:Case-Control Studies; D004200:Diseases in Twins / Q000235:genetics / Q000503:physiopathology*; D006801:Humans; D008297:Male; D000857:Olfaction Disorders / Q000209:etiology* / Q000235:genetics; D010300:Parkinson Disease / Q000235:genetics / Q000503:physiopathology*; D011237:Predictive Value of Tests; D012016:Reference Values; D012680:Sensitivity and Specificity; D012903:Smell / Q000502:physiology*; D013997:Time Factors; D014427:Twins