Unlike patients with Alzheimer's - who have both beta-amyloid plaques and tangles in the brain - those with PART only have tangles.
The research team - co-led by Dr. Peter T. Nelson of the Sanders-Brown Center on Aging at the University of Kentucky and Dr. John F. Crary of Mount Sinai Hospital in New York, NY - call the disease primary age-related tauopathy (PART).
Patients with Alzheimer's disease have tangles in their brain made up of a protein called tau, as well as plaques caused by build-up of a protein called beta-amyloid. But the team says that patients with PART only have tangles, not plaques.
The fact that some patients have memory complaints but only have tangles in their brains has long baffled researchers. In the past, such patients have been described as being in the very early stages of Alzheimer's. However, studies have shown that these patients have no abnormal beta-amyloid in their brains, indicating that they will not develop plaques, which are a hallmark of Alzheimer's.
With this in mind, Dr. Nelson, Dr. Crary and their team set out to establish new clinical criteria for diagnosing PART - something they hope will lead to the development of better treatments for patients with varying types of memory disorders.
Unlike Alzheimer's, tangles in PART are restricted to specific brain areas
In their study, published in the journal Acta Neuoropathologica, the researchers say PART is a direct result of brain tangles consisting of tau protein.
In Alzheimer's, tangles often form all over the brain. In PART, however, tangles tend to form in patients' medial temporal lobe, basal forebrain, brainstem and olfactory regions. Many of these structures are related to memory, the team notes, which explains why patients with PART experience memory problems.
As yet, the researchers say they are unable to determine how common PART is. But they point out that it tends to be more severe in very elderly individuals, although they do not yet know the reasons behind this.
What is more, some studies have shown that up to 25% of patients with mild cognitive impairment - who have undergone brain scans and have had their cerebrospinal fluid tested for biomarkers of beta-amyloid and tau - have no signs of abnormal beta-amyloid, suggesting they may have PART.
Dr. Nelson talks more about the criteria of PART in the video below:
Commenting on their study, Dr. Nelson says:
"Until now, PART has been difficult to treat or even study because of lack of well-defined criteria. Now that the scientific community has come to a consensus on what the key features of PART are, this will help doctors diagnose different forms of memory impairment early.
These advancements will have a big impact on our ability to recognize and develop effective treatments for brain diseases seen in older persons."
In addition, the team says their new criteria for PART may help boost the accuracy of clinical trials testing medication for Alzheimer's. They explain that in the past, PART patients may have negatively impacted clinical trials testing drugs that target amyloid-beta, as these drugs would not have been effective against tangles.
Medical News Today recently reported on a study suggesting that in patients with mild cognitive impairment, anxiety could speed up onset of Alzheimer's.