While it is common knowledge that HIV is the cause of the AIDS virus a lesser-known fact is that there are actually different sub types of the condition. A new study concludes that patients infected with certain sub types are more likely to develop dementia than those affected with other strains of HIV.

The HIV sub types are divided by letter, A to K, and are distinguished from one another by small differences in genetic makeup. Some strains seem to center around a particular region of the world and others have been identified in the past to be more likely to cause the onset of full blown AIDS than others. Although there are over 35 million people living with HIV infections across the world the majority live in sub – Saharan Africa, where previous studies have found that types A, C and D are most dominant.

In his previous research Ned Sacktor, M.D and his co authors and colleagues found that approximately 31 percent of those patients seen at a clinic in Kampala, the Ugandan capital, displayed signs of dementia. They already knew that in that particular region the HIV subtypes A and D were most commonly found. The researchers began to wonder if patients who had different subtypes of HIV were more likely to develop dementia than others.

Their new study focused on 60 of the clinic’s HIV infected patients, all of whom had been asked to participate in a different study to test the effectiveness of certain anti retro viral drugs on cognitive impairment but at the time of Sacktor’s observations they had yet to begin taking the drugs. The patients were divided into groups according to which subtype of the HIV virus they possessed.

They were not surprised to discover that the majority of their study sample had either the A or D subtype.

Out of the 33 type A patients it was determined that seven suffered from dementia ,  about 24%,while among those with HIV D , nine patients in all, eight were afflicted with the cognitive condition, an astonishing 89% rate of occurrence.

According to Sacktor, who is a professor of neurology at the Johns Hopkins University School of Medicine and a clinician at the Johns Hopkins Bayview Medical Center, they were surprised by the dramatic difference in dementia rates between the patients. He theorizes if those results are repeated across sub Saharan Africa HIV induced dementia may be one of the most common, but as of yet unrecognized, forms of the disease.

Sacktor and his colleagues theorize that the D strain of the HIV virus may cause more inflammation and injury to the brain than other types, something that will be the focus of their future research.