Lay summary
Many people with Parkinson's are at risk of dementia but we have been unable to predict when that will occur. We will do advanced brain scans (MRI and PET), gene testing and clinical evaluations in 85 Parkinson's patients who have mild cognitive impairments, who we know are at higher risk, and then determine whether they progress to dementia over the subsequent three years. By identifying characteristics present in the scans and genetic tests of those who develop dementia, compared to those who do not, we can advance our understanding of this important issue and establish a useful and reliable tool for researchers and clinicians. It is critical that we can do this so that preventative treatments to protect against dementia can be targeted at the most appropriate patients when that treatment becomes available, and to select the right ""at risk"" Parkinson's patients for trials of new treatments.