The Young Onset Dementia Assessment Study (YODA) is a longitudinal prospective cohort study with multiple aims, including: a) Improve the understanding of the changes in the brains of sufferers and how the disease develops; b) To promote the development of evidence-based guidelines to inform clinical decision-making and improve health outcomes for participants; c) To provide a platform to support the design and conduct of clinical trials; and d) To maximize the use of routinely collected clinical data to optimize future use of such information.