Researchers at the Karolinska Institutet in Solna, Sweden, found the size of tau deposits in brains of Alzheimer's patients and the speed of their spread vary from patient to patient.

The data was revealed in Molecular Psychiatry, with research led by Agneta Nordberg, a professor in Karolinska’s department of neurobiology, care sciences and society. Nordberg and her team used PET imaging to measure the spread of tau deposits and amyloid plaque linked with Alzheimer’s disease. They also charted the energy metabolism of the brain cells, monitoring the disease over time to see how the three parameters changed.

"There's been an international race to measure tau spread, and we probably got there first," says Nordberg in a statement. "There are no previous reports on how tau deposits spread after 17 months into the disease. Our results can improve understanding of tau accumulation in Alzheimer's disease, help ongoing research to quantify the effect of tau vaccines and enable early diagnosis."

For the study, researchers examined 16 patients at different stages of Alzheimer’s disease from the memory unit at Karolinska Hospital. Every 17 months, patients underwent a series of neurological memory tests and PET scans. All participants had a sizeable amount of amyloid plaque deposition in the brain. The size and speed of spread of their tau deposits varied significantly between individuals.

"We also saw a strong direct correlation between size of deposit and episodic memory impairment," Nordberg said. "This could explain why the disease progresses at such a varying rate from one patient to the other. That said, tau doesn't seem to have much of an effect on the global general memory, which is more reasonably related to brain metabolism."