The purpose of this funding opportunity announcement (FOA) is to support efficient natural history studies alone or in conjunction with the development and validation of clinical outcome assessments (COAs) and/or biomarker studies to address the unmet needs in rare neurodegenerative diseases for children and adults. Through the support of studies with high quality and interpretable data elements, FDA expects to address critical knowledge gaps, remove major barriers to progress in the field, exert a significant and broad impact on a specific rare neurodegenerative disease or multiple rare neurodegenerative diseases with similar pathophysiology, and facilitate rare disease product development.