from article in New Scientist, B. Vastag, march 17, 2007 vol171. p. 163

"Implanted stem cells grow 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, 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.
Evan Y. Snyder, who led the work at the Burnham Institute for medical research in LaJolla, Calif, says that the implanted cells knew exactly how to repair the brain:"even the dumbest stem cell is smarter than the smartest neurologist."
The stem cells created all the major brain-cell types, including active neurons and support cells called astroglia and oligodendrocytes...reported in Nature Medicine.
This "mileu" restored enzyme production and reduced brain inflammation a hallmark of many neurodegenerative diseases, says Snyder. "We saw a series of actions that try to return (the brain) to baseline."
....Snyder is at the forefront of a movement that champions stem cells as "factories" that might repair and protect brain tissue, not just replace damaged neurons...
...Mice in the experiment lacked the gene for hex, the enzyme lacking in Sandhoff disease--one of the lyposomal storage diseases. The donor cells, implated at birth, spawned a new generation of cells that produced enough hex to enable the host cells to clear lipids. that delayed onset and extended life by 70% over that of mutant mice not getting the implants.
"The good news was they performed almost identically, says Snyder...
In a new series of experiemnts Snyder's group is implanting a second dose of stem cells in mice that had been treated at birth but in which Sandhoff-like symptoms had appeared. "This is how I would do it in patients," he says.
...Stem Cells Inc of Palo Alto, Calif. is already testing the safety of such cells in children with Batten disease, another lysosomal-storage