Many people living with HIV report having memory loss or other cognitive problems that can sound a lot like early-onset Alzheimer's disease. Unlike their senior counterparts, however, cognitively impaired people with HIV are often in their 40s and 50s—and the early decline can make it difficult to hold jobs and maintain personal lives.

Researchers have been looking for similarities between the two diseases for years. And new findings, published online today in the journal Neurology, have confirmed a key commonality: abnormal distribution of a protein known as amyloid beta.

"I really did not expect the biology of HIV cognitive dysfunction to be related to Alzheimer's," David Clifford, a professor of neurology and medicine at Washington University School of Medicine in St. Louis and lead study author, said in a prepared statement. But that is just what his team found, backing up results from smaller studies that had posited the link a few years ago.

Sampling brain and spinal fluid from Alzheimer's, HIV-infected and control volunteers, researchers found that both people with HIV showing cognitive decline and people with Alzheimer's have strikingly low amounts of amyloid beta protein in their spinal fluid compared to the healthy, control volunteers and those with HIV who had normal cognitive function. (In those with Alzheimer's, amyloid beta levels dip in the spinal fluid as they increase in the brain, where it is suspected to contribute to some of the physical damage seen in post-mortem studies.)

Despite this fundamental similarity, "HIV patients with cognitive dysfunction don't have early Alzheimer's," Clifford said. The study uncovered an absence of key Alzheimer's disease flags, such as excess tau protein, in the HIV-positive individuals. "If you look at the brains of HIV patients with cognitive impairments, they don't look like Alzheimer's brains," Clifford said. "They don't have the same atrophy or a plethora of plaques and tangles characteristic of Alzheimer's."

Researchers in the field continue to debate whether the hallmarks of early dementia in those with HIV are a result of the disease itself or the extensive, long-term treatments. Just last week, the World Health Organization recommended earlier treatment for the world's 33.4 million people with HIV, which will likely make some 3 million to 5 million more people eligible for antiretroviral therapies. The Neurology paper authors, some of who have served on the boards of pharmaceutical companies involved in HIV drug research, did not point to the therapies—which most of the study's HIV-positive people were taking—as a likely cause. Clifford noted that, "We see it even in patients who haven't received HIV therapy."

In the meantime, hundreds of thousands of the more than 1 million U.S. residents estimated to be living with HIV are likely suffering from some sort of cognitive decline—whether subtle or more serious. And as drug therapy continues to improve the quality and length of patients' lives, more are expected to turn up with these new symptoms of the virus. "I have many [HIV] patients who say their personalities have changed," Anthony Geraci, a clinical assistant professor of Neurology at Mount Sinai School of Medicine in New York City, told New York magazine last month.

Image courtesy of iStockphoto/twohumans