The discovery of a link between death receptor 6 and APP is important because it suggests that Alzheimer's may be caused when the normal self-destruction mechanism of excess nerve cells in embryos is somehow hijacked or turned back on in adults, says Tessier-Lavigne. "If the theory is correct, we may be able to attack Alzheimer's in a new way with drugs that can block this biochemical pathway," he adds. The new discovery published Wednesday by Genentech researchers is just a start. The company has a long way to go before this new theory on the cause of Alzheimer's can be proven, and even longer before new drugs are developed that may be effective against the disease. Still, the Genentech research adds to the body of knowledge about the possible causes of Alzheimer's. Much of the ongoing work in the field is being directed at developing drugs that can break down toxic beta amyloid in the brain. So far, however, that work hasn't produced much in the way of positive results. Drugs from Myriad Genetics ( MYGN) and Neurochem have failed, while another drug from Elan ( ELN) and Wyeth ( WYE) has produced only lackluster results so far in mid-stage studies. Pfizer, Transition Therapeutics ( TTHI) and Eli Lilly ( LLY) also have so-called "beta-amyloid drugs" under development. "We still don't understand the relative contribution our new discovery plays in Alzheimer's compared to other mechanisms such as beta amyloid," says Tessier-Lavigne, adding that more research needs to be done to see if there are ways in which they might be complementary. Meantime, Genentech also is moving ahead on multiple fronts in Alzheimer's drug research. The company bought rights to a beta amyloid drug from privately held Swiss company AC Immune. That drug is currently in a phase I study, but Genentech hasn't disclosed when the study is expected to be completed. Genentech shares closed up $1.70, or 2%, to $84.70 on Wednesday.