This trans-NIH program has two main goals: To provide answers to patients with mysterious conditions that have long eluded diagnosis and To advance medical knowledge about rare and common diseases. Any medical condition that eludes diagnosis by a referring physician can be considered undiagnosed and may be of interest to this pilot study. Some patients wait years for a definitive diagnosis. For this study, only a fraction of cases referred will be invited to proceed in the study at the discretion of the programs medical team. Patient medical evaluations will yield valuable information medical researchers will use to: Help identify previously unrecognized rare diseases Suggest new ways to treat and prevent common illnesses, and Determine promising options for continued medical research