Disease stages and therapeutic hypotheses in two decades of neurodegenerative disease clinical trials

Background: Neurodegenerative disease is increasing in prevalence and remains without disease-modifying therapies, and most trials of new drugs fail. Proposed solutions include aiming upstream: targeting molecular root causes of disease and testing therapies earlier, even at pre-symptomatic stages. We sought to understand what disease stages were eligible to enroll in neurodegenerative disease clinical trials in recent years and what molecular targets were tested in these trials. Methods: We combined automated analysis and manual curation of trial registrations from ClinicalTrials.gov for Alzheimer’s disease, Parkinson’s disease, frontotemporal dementia / amyotrophic lateral sclerosis, and Huntington’s disease. Findings: 3,241 trials from 2000-2020 were curated. Industry-sponsored drug trials, a minority (34%) of trials but a majority (61%) of patient-years, were more likely to complete, to have specified phase, and to have placebo or standard-of-care control arms. The mean number of inclusion and exclusion criteria more than doubled over this period, and eligible score ranges shrank. Trials have shifted towards less severely impaired participants, but only 2.7% of trials were open to pre-symptomatic individuals and these were depleted for industry sponsors (OR = 0.32) and for drug trials (OR = 0.59), instead being enriched for behavioral interventions (OR = 3.1). 16 novel, genetically supported therapeutic hypotheses have been tested in drug trials, with a mean lag of 13 years from genetic association to first trial. Such trials comprised just 18% of patient-years. Interpretation: Eligibility criteria for trials have shifted towards earlier, milder disease stages but are still overwhelmingly focused on symptomatic patients, particularly for industry-sponsored drug trials. Drugs targeting disease genes supported by human genetics comprise a small fraction of drug development effort, and their success may be hindered by a focus on symptomatic patients.