Brain Fix: Stem cells supply missing enzyme

Implanted stem cells grew into a range of beneficial brain-cell types and greatly extended the lives of mice missing an important enzyme, researchers report. Furthermore, stem cells from mouse brains, from human-fetal brains, and from human embryos proved equally adept at battling the mouse version of Sandhoff disease. In people, that congenital enzyme deficiency is similar to Tay-Sachs disease and causes severe mental retardation and early death.