If there is a holy grail of genetic mysteries, Alzheimer disease certainly qualifies—with Richard Mayeux hot on its trail. Mayeux has spent the past 18 years trying to tease out the complex genetic causes of late-onset Alzheimer disease.

Mayeux, co-director of Columbia University's Taub Institute for Research on Alzheimer's disease and the Aging Brain, appears to be on the brink of nailing a culprit, nearly 13 years after the discovery of APOE, the only gene known in its mutated form to be associated with the common, late-onset form of the disease. Mayeux has painstakingly built a database of clinical histories and cell lines from about 500 Dominican families prone to the late-onset form of the disease. He won't reveal more about the candidate he and his collaborators are pursuing because the findings are unpublished.

If there were a treatment or a cure, then by all means it would be important to have genetic testing.

The mere mention of a new Alzheimer gene is sure to stoke the ongoing debate about genetic testing. Like many scientists, Mayeux supports genetic tests for individuals from families that carry mutations for the early-onset disease, especially for those considering having children. But for the late-onset disease, which comprises more than 98% of cases, Mayeux is vocally opposed to testing.

“If there were a treatment or a cure, then by all means it would be important to have genetic testing,” says Mayeux. “Until that happens, I really think it's inappropriate.”