Investigators from The University of Texas Health Science Center at San Antonio led the study that provides more conclusive evidence of a link for the protein, called apoE4, to infectious diseases such as HIV.

The scientists studied 1,300 European and African-American HIV-infected patients, comparing HIV clinical outcomes of individuals who have two copies of the gene that makes the apoE4 protein with outcomes of those endowed with two copies of a gene that makes a related protein, apoE3. The latter differs from apoE4 by a single amino acid.

They found people with two copies of apoE4 were more likely to have a two-fold faster HIV disease course, noticeably marked by progression to death, than subjects with two copies that make apoE3.

"The prevailing view is that apoE4 plays a role only in non-infectious diseases such as Alzheimer's but we found clear evidence to the contrary," said study co-author Dr. Sunil Ahuja, a professor of medicine, microbiology, immunology and biochemistry.

The report appears in the early online edition of the Proceedings of the National Academy of Sciences.