Shares in the drug makers Wyeth and Elan plunged on Wednesday after their experimental Alzheimer’s treatment showed no result in the majority of patients and was linked to a brain-swelling condition called vasogenic edema.

The drug, bapineuzumab, is the first treatment shown to help patients by removing spaghetti-like clumps of protein that accumulate in their brains.

The drug, made by Elan Corp and Wyeth, did slow memory loss in some patients better than existing treatments, but it had no effect in people with the ApoE4 gene, which is found in about half of all Alzheimer’s patients, Bloombergnews reported. Twelve cases of vasogenic edema occurred in the trial of 234 patients, and 10 of those cases occurred in patients with the ApoE4 gene, the same source reported. Patients who were given a higher dose didn’t record stronger benefits.

Bapineuzumab works by removing clumps of protein that accumulate in the brains of Alzheimer’s patients. Alzheimer’s disease has been identified as a protein misfolding disease but also as a tauopathy due to abnormal aggregation of the tau protein. The drugs may work by dissolving tangles of the protein (tau protein) that collects in the brain cells of Alzheimer’s patients. A key enzyme called memapsin 2, or beta-secretase, is also involved in the development of Alzheimer’s disease. The action of that enzyme on a protein determines the formation of plaques – which are made of small peptides called beta-amyloid, a protein fragment from a larger protein – in the brain.

The companies have seen their shares rise after they announced the partial results of the phase 1 of the study. Last month the Dublin, Ireland based Elan’s shares’ price had reached the highest level in three years on the London stock market.

But researchers told the International Conference on Alzheimer’s Disease in Chicago that the drug raised the risks of potential side effects in the brain.

“We believe that today’s results leave unanswered questions about the efficacy profile of bapineuzumab,” Chris Schott, a JP Morgan analyst said in a research note.

Citigroup Inc. analyst John Boris recommended investors to sale their shares of Wyeth.

“We removed bapineuzumab from our model, as the likelihood of phase three clinical success, regulatory approval and commercial success are extremely low,” he said in a note to investors according to Bloomberg.

Wyeth fell $5.37, or 12 percent in New York Stock Exchange composite trading.

The companies have already begun phase 3 clinical trials of the drug.

Alzheimer’s affects about five million people in the United States. Alzheimer’s disease is a degenerative and terminal disease for which there is no known cure. In its most common form, it afflicts individuals over 65 years old. As the disease advances, progressive symptoms include confusion, anger, mood swings, language breakdown, long-term memory loss. The causes of the progression of Alzheimer’s disease are not well-understood.

According to the Alzheimer’s Society of Canada, more than 300,000 Canadians with ages over 65 are currently suffering from the disease and 97,000 more are expected to develop the condition.

It is estimated that 26.6 million people worldwide were afflicted by AD in 2006. The number of patients with Alzheimer’s disease will grow in the next years and will reach more than 106 million by 2050, a study led by researchers at the Johns Hopkins Bloomberg School of Public Health showed.