New York, Nov 14 (IANS): Alzheimer's disease now has a new cousin as an international team of researchers has determined criteria for a new neurological disorder called primary age-related tauopathy (PART).

Patients with PART develop memory impairment that is not at all different from those suffering from Alzheimer's disease, but they lack plaques in the brain, formed from the accumulation of amyloid protein.

Amyloid plaque is the hallmark of Alzheimer's disease.

"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," explained Peter Nelson, a professor of neuropathology at the University of Kentucky.

"However, autopsy studies have demonstrated that some patients have tangles but no plaques and we have long wondered what condition these patients had."

Individuals who have tangles resembling those found in Alzheimer's but have no detectable amyloid plaques should now be classified as PART, the researchers proposed.

Awareness of this neurological disease will help doctors diagnose and develop more effective treatments for patients with different types of memory impairment, they added.

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.

In the current study, investigators from the US, Canada, Europe, and Japan came together to formalise criteria for diagnosing this new neurological disorder.

PART is most severe in patients of advanced age, but is generally mild in younger elderly individuals.

The study appeared in the journal Acta Neuoropathologica.