Smell identification ability in twin pairs discordant for Parkinson's disease.

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.