This video describes the case of a patient with retinitis pigmentosa (RP), a progressive disease that leads to blindness, and how physician-scientist Dr. Ed Stone approached the search for the causal mutation. Just before his sophomore year in college, Sam Walker was diagnosed with RP, which can be caused by mutations in one of over 100 known genes. Dr. Ed Stone set out to identify the specific mutation affecting Sam, with the hope of devising a treatment for him. The process involved 1) testing Sam’s DNA for mutations known to be associated with RP in other patients, 2) analyzing the sequences of genes not previously associated with RP to search for novel causative mutations in Sam, 3) finding additional RP patients with the same mutation as Sam, and 4) determining the effect of Sam’s mutation in a model organism. Having identified the likely root of Sam’s RP, Dr. Stone can now devise a gene therapy to stop disease progression.