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Introduction
Parkinson's disease (PD) affects 1% of individuals over the age of 60 years. 1 2 The clinical diagnosis of PD is often made late and current treatments address symptoms and not the underlying disease process. 3 A key priority in PD is early detection and treatment with drugs that have disease-modifying effects. 4
Many initiatives have been set up to identify individuals or groups at risk of PD. 5 These include longitudinal studies in groups that have an excess background risk of PD and studies using proposed screening tests to delineate risk. 6-10 Due to the cost and availability of these tests, a non-invasive, widely available and inexpensive method to select groups for further investigation would be desirable.
A large number of historical risk factors and early non-motor features of PD have been reported from observational studies. Recently, our group reported a systematic exploration of factors that can be screened for in a primary care setting. 11 In parallel to this, we initiated the PREDICT-PD study; an internet-based study in the UK general population to identify a group at higher risk of PD, using an algorithm that estimates the possible risk of developing PD from information that can be collected using online tools. We describe here the development of the preliminary algorithm derived from the results from the systematic review of published literature. 11 The performance of this preliminary algorithm was assessed by comparing the occurrence of a combination of proxies for future PD, including three of the strongest individual markers of increased PD risk (smell loss, report of REM sleep-behaviour disorder (RBD) and finger-tapping speed), in those estimated to be at higher risk of PD alongside those estimated to be at lower risk. Confirmation of validity will be tested in the longitudinal follow-up of study participants, using incident PD diagnosis as the outcome.
Methods
The study was approved by Central London Research Committee 3 (reference number 10/H0716/85). Participants were recruited via the study website following a limited advertising campaign on local radio and in magazines with an older readership, and by email to members of the Parkinson's UK charity. Participants submitted an online consent form before passing to the secure test area. Inclusion criteria in this phase were residency in the UK and...