A growing number of clinics and hospitals worldwide are offering unproven and potentially dangerous stem cell therapies to treat diabetes, multiple sclerosis, Alzheimer's and Parkinson's diseases, spinal cord injuries and other ailments, and Nobel laureate Shinya Yamanaka warned consumers away from these unproven treatments. "If there are no preclinical data in the efficiency and safety of the procedure ... it could be very dangerous," he said. Yamanaka and John Gurdon share this year's Nobel Prize in Medicine for their work on induced pluripotent stem cells.