A drug under development by Salt Lake-based Myriad Genetics to treat Alzheimer's disease failed in a closely watched late-stage clinical trial, dealing another blow to efforts to combat the illness.

Myriad said the drug, called Flurizan, did not improve thinking ability by a statistically significant amount compared with a placebo. Nor did it improve the ability of patients to carry out daily activities. The company said it would discontinue development of the drug.

Myriad's stock fell more than 5 percent Monday, closing at $45.52.

The failure is significant because Flurizan was one of the first drugs to reach late-stage testing that was seen as working by trying to prevent the buildup of toxic amyloid plaques in the brain.