SFGate looks at one of the promising uses of stem cells in practice: as testbeds to uncover biochemical mechanisms in neurodegenerative disorders. "Researchers reported evidence Sunday as to what may be causing ALS, or amyotrophic lateral sclerosis, which is marked by the loss of specialized nerve cells, known as motor neurons, that drive conscious movement. The studies implicate a toxic factor in the cellular environment surrounding the motor neurons, rather than something in the neurons themselves. That means any transplanted nerve cells - even healthy motor neurons produced in pristine laboratory conditions from colonies of human embryonic stem cells - would probably die, too, if implanted in an ALS patient. But that doesn't mean stem cells are useless in treating ALS - in fact, they were used in the very laboratory experiments that produced the latest findings. ... Further research is under way to identify the toxin, and perhaps find out how the astrocytes go awry, possibly through some combination of genes and environmental exposure. Eventually, researchers may be able to concoct a drug to neutralize the poisonous effect or use some other strategy to make nerve cells resistant."