A small biotech company that trumpeted an exciting new treatment for Alzheimer’s disease is now under fire for irregularities in its research results, after several studies related to its work were retracted or questioned by scientific journals.

Cassava Sciences, based in Austin, Texas, announced last summer that its drug, simufilam, improved cognition in Alzheimer’s patients in a small clinical trial, describing it as the first such advance in treatment of the disease. Cassava later initiated a larger trial.

The drug’s potential garnered enormous attention from investors. Alzheimer’s disease affects roughly 6 million Americans, a number expected to double by 2050, and an effective treatment would be lucrative. Cassava’s stock soared, by more than 1,500% at one point. The company was worth nearly $5 billion last summer.