Hundreds of patients throughout the USA and the world develop illnesses which have no known cause. Often a genetic origin is likely but it is very hard to track down the genes responsible. The Undiagnosed Diseases Program of the NIH has some genomic analysis tests that are not yet available at other hospitals in the US. In this 15 minute film two patients and their families explain just how tough this situation can be. Head of program Bill Gahl explains some of the science behind the program and offers hope for the future.