Pfizer Inc. said on Monday that a closely watched experimental Alzheimer’s drug failed to slow the disease in one late-stage study, but the drug maker said it will continue to study the drug’s effect on a different group of patients.

Pfizer, which is testing bapineuzumab with partner Johnson & Johnson, said the injected drug didn’t slow mental or functional decline in patients with mild or moderate Alzheimer’s disease. The study included patients who carry a gene called ApoE4, which gives people a higher risk of developing the memory-robbing disorder.

About half the population does not carry that gene, however, and Pfizer says a study of the drug in patients without the gene is continuing. Results of that study are expected to be announced later this summer.

Johnson & Johnson spokeswoman Ellen Rose said scientists who conducted mid-stage tests on bapineuzumab “saw a hint that the people who are carriers of the ApoE4 gene might not have as good a chance as people who are not carriers.”

New York-based Pfizer and Johnson & Johnson, based in New Brunswick, New Jersey, are each running two studies of the experimental drug.

Current medicines for Alzheimer’s disease temporarily control symptoms such as memory loss, confusion and agitation. But they do nothing to slow, stop or reverse mental decline, leaving patients and their loved ones desperate for a new treatment.

Finding a drug that could at least slow the disease has become a sort of Holy Grail in the pharmaceutical industry. A successful medicine would be guaranteed to generate billions in annual sales, given the world’s aging population.

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