In April, the future was looking bleak for an experimental Alzheimer's drug called valiltramiprosate, or ALZ-801.

Researchers had just released topline results of a study of more than 300 people age 50 or older, who were genetically predisposed to Alzheimer's. Overall, those who got the drug did no better than those given a placebo.

But in September, a closer look at the results revealed benefits for a subgroup of 125 people who had only mild memory problems when they started taking the drug.

Those participants, initially diagnosed with mild cognitive impairment rather than mild dementia, "showed very meaningful responses," says Dr. Susan Abushakra, chief medical officer of Alzheon, the drug's maker.

By one measure, the drug slowed cognitive decline by 52% in people with mild c

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