In Reply We agree with Noyce and Lees that developing an effective strategy to identify individuals with prodromal Parkinson disease (PD) is challenging and that implementing that strategy will be costly. In the Parkinson’s Associated Risk Study (PARS), we used the combination of smell identification testing followed by dopamine transporter (DAT) imaging to identify individuals from the general population who were at risk for conversion to a clinical diagnosis of PD.1 The purpose of the 2-stage process is to improve cost efficiency by reducing the number of individuals who receive DAT imaging, While the current PARS study identified only 23 participants who were at high risk, the mail-out olfactory testing is scalable and represents a modest study cost. Given the high conversion rate in PARS (40% at 3 years), we estimate that it would require about 90 participants per group to detect a 50% risk reduction in the rate of conversion after 3-year follow-up due to treatment with a putative disease-modifying therapy. While still a difficult, long-term, and expensive study, the potential benefit from randomized clinical trials that test drugs that might prevent or delay onset of PD is enormous. We recognize that there will likely be many iterations of a preclinical paradigm for studies of disease-modifying therapies, but our initial study has proven the feasibility of identifying patients who are very likely to develop PD and offers hope for more effective therapies in the future.
Jennings D, Siderowf A, Marek K. Observations on a 2-Step Approach to Screening for Parkinson Disease—Reply. JAMA Neurol. 2017;74(12):1506–1507. doi:10.1001/jamaneurol.2017.3208
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