It's a devastating disease driving a dementia epidemic ruining tens of millions of lives, but with no new medical treatment since the turn of the century, the fight against Alzheimer's is foundering.
Despite decades of research and hundreds of millions of dollars, the precise cause of the neurodegenerative disease — which leaves victims suffering from memory loss, disorientation, and behavioural problems — remains poorly understood.
"It's a bit like solving a jigsaw puzzle without knowing what the end result needs to look like," said Pierre Tariot, director of the Banner Alzheimer's Institute in Phoenix, Arizona.
This year alone, pharmaceutical giants — including Lundbeck, Takeda, Merck & Co, Janssen Biotech, AstraZeneca, and Eli Lilly — have either halted or failed in their search for a new Alzheimer's drug.
U.S. drug giant Pfizer said in January it was abandoning all research into the disease.
The problem, according to Marie Sarazin, director of neurology at the Saint-Anne Hospital in Paris, is that scientific research has followed "the same track" for decades.
After trials on mice focused on diseased neurons in the brain appeared to produce a breakthrough in the early 2000s, many corporations "thought they'd hit the jackpot," Sarazin said.
But follow-up research has so far failed to produce a new medical treatment for Alzheimer's. Indeed, the long-held hypothesis over what causes the disease in the first place is now being reconsidered.
Alzheimer's occurs when neurons in the brain lose their ability to communicate with one another, leading patients to struggle to remember names and places, orientate themselves, or interact with loved ones.
Worldwide, about seven percent of people over 65 suffer from the disease or some form of dementia, a percentage that rises to 40 percent above the age of 85.
The number afflicted is expected to triple by 2050 to 152 million, according to the World Health Organization, posing a huge challenge to healthcare systems.
Alzheimer's cost an estimated $818 billion (700 billion euros) in 2015 — equivalent to around one percent of global GDP, and this is predicted to double by 2030.
Friday is World Alzheimer's Day, an event launched in 2012 to raise global awareness of the disease. It comes this year with a glimmer of promise for a breakthrough: A joint U.S.-Japanese clinical trial of an antibody designed to breakdown proteins thought to hamper neuroactivity significantly helped the brain function of test subjects.
On Wednesday, a team of scientists in the U.S. said they had eliminated dead-but-toxic cells occurring naturally in the brains of mice designed to mimic Alzheimer's and slowed neuron damage and memory loss associated with the disease.
But with developed nations dealing with the health challenges posed by aging populations, many experts agree that more attention must focus on prevention as well as cure. Exercise, drinking less alcohol, and eating a balanced diet have all shown to reduce the risk of developing Alzheimer's.
"It seems that like in any other neurodegenerative disease, the key will be to go into prevention, as early as possible, before signs and symptoms of the pathology occur," Danny Bar-Zohar, global head of neuroscience development at Novartis, told AFP.