not only from the quantitative point of view, but also for currently unknown and unexpected secondary effects of the vector or the transgene. Some of these approaches have already been tested in the clinic, but much more needs to be done to understand the human conditions treated and the n- ural history of their pathology. We are indebted to the secretarial assistance of Ms. Lin Wells (Bone and Joint Research Unit, London, UK) and the help of Hans Detlef Klüber for his help in getting this book published. We hope this book will be of interest to c- nicians and scientists and inspiring to students of the subject who will use their own ingenuity and knowledge to further forward this discipline into clinical use.