A new study has defined and established criteria for a new neurological disease closely resembling Alzheimer's disease called primary age-related tauopathy (PART).

The multi-institutional study co-led by Peter T. Nelson of the University of Kentucky's Sanders-Brown Center on Aging, and John Crary of Pathology & Neuroscience with Mount Sinai Hospital has found that patients with PART develop cognitive impairment that can be indistinguishable from Alzheimer's disease, but they lack amyloid plaques.

Plaques in the brain, formed from the accumulation of amyloid protein, are a hallmark of Alzheimer's disease. Until now, researchers have considered cases with only tangles to be either very early-stage Alzheimer's or a variant of the disease in which the plaques are harder to detect. However, previous in-depth biochemical and genetic studies have failed to reveal the presence of any abnormal amyloid in these patients. Although tangle-only patients can have memory complaints, the presence of plaques is a key requirement for an Alzheimer's diagnosis.

"To make an Alzheimer's diagnosis you need to see two things together in a patient's brain: amyloid plaques and structures called neurofibrillary tangles composed of a protein called tau," Nelson, a professor of neuropathology at the University of Kentucky's Sanders-Brown Center on Aging, said in a statement. "However, autopsy studies have demonstrated that some patients have tangles but no plaques and we've long wondered what condition these patients had."

In the recent study, researchers formalized criteria for diagnosing this new neurological disorder. The study establishes that PART is a primary tauopathy, a disease directly caused by the tau protein in tangles.

PART is most severe in patients of advanced age, but is generally mild in younger elderly individuals. The reason for this is currently unknown, but unlike Alzheimer's disease, in which the tangles spread throughout the brain, in PART cases the tangles are restricted mainly to structures important for memory.

"Until now, PART has been difficult to treat or even study because of lack of well-defined criteria,"Nelson added. "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."

Researchers said it is too early to tell how common PART is, "but given that tangles are nearly universal in the brains of older individuals, it might be more widespread than generally recognized."

The findings are detailed in the current issue of Acta Neuoropathologica.