Understanding the natural history of a disease - its characteristics. management. and outcomes with or without treatment - is critical for developing new therapies. identifying best practice guidelines for treatment and improving patient outcomes. The natural history of a disease may vary across different groups or geographic regions. and it often changes over time as new therapies are introduced. In many cases. the natural histories of diseases are not well described. The need to develop and conduct studies to better understand the natural history of diseases has been recognized by a wide range of stakeholders. including funding agencies regulatory bodies researchers. clinicians. and patient advocacy groups. These stakeholders are increasingly turning to patient registries as effective tools for studying the natural history of diseases.