Thousands "misdiagnosed" with Alzheimer's disease as discovery may pave way for new research on dementia

Hundreds of thousands of people diagnosed with Alzheimer's disease are likely to be suffering from a different disease, which is why drug tests continue to fail, scientists said.

In new findings hailed as the "most important research to be published on dementia in the last five years," experts said that about one-third of people over the age of 85 are suffering from late-onset disease despite showing signs of Alzheimer's.

Alzheimer's disease is caused by the buildup of sticky plaques of amyloid and tau proteins in the brain, damaging brain cells, leading to memory loss and confusion. For years, scientists have noted that large numbers of elderly people who died of Alzheimer's had no amyloid or tau in their brains.

Instead, they appeared to have an accumulation of a different protein known as TDP-43.

The finding is important because most Alzheimer's drug tests have focused on clearing the amyloid, and all have so far failed, prompting the major drug companies to abandon the research.

Pete Nelson, of the University of Kentucky, who led the research, said, "Delayed illness probably responds to treatments other than Alzheimer's disease, which may help explain why so many Alzheimer's remedies have failed clinical trials."

Like Alzheimer's disease, the late disease affects the capacity of memory and thought. However, it develops more slowly than Alzheimer's disease.

Researchers have found that about 25% of people over 85 have TDP-43s with bending problems to affect their memory or thinking skills, and more can have the disease without symptoms.

Independent Irish