Developing therapeutics for rare diseases can be challenging, and not just because of the small patient populations. Often the progression of a disease is not well understood, the patient population can be heterogenous, and the development of objective and meaningful endpoints for a trial can be difficult. We spoke to Ralf Rosskamp, chief medical officer of Dicerna, about how his company has navigated the various challenges in its effort to develop a treatment for a rare liver disorders, how it finds patients, and how it determines endpoints.