Researchers are closer to finding a better way to treat children with a rare metabolic disorder called MPS I. It is caused by a deficiency of the key enzyme IDUA needed to break down complex sugars in cells. MPS I eventually leads to the abnormal accumulation of sugar debris and cell death. The two main treatments are bone marrow transplantation and intravenous enzyme replacement therapy; however, both are only marginally effective or clinically impractical, especially when the disease enters the central nervous system (lat. Systematis nervosi centralis, CNS).