Methods and compositions relating to motor neurons derived from induced pluripotent stem cells of subjects having a neurodegenerative disease, where the motor neurons exhibit phenotypes characteristic of the neurodegenerative disease, are provided herein. In particular, the present invention provides methods for screening putative therapeutic agents and methods for diagnosing living subjects as having a neurodegenerative disease. In addition, the present invention provides therapeutic gene transfer methods for treating or preventing a neurodegenerative disease in a subject in need thereof.