People with more copies of a gene that helps to fight HIV are less likely to become infected with the virus or to develop AIDS than those of the same geographical ancestry, such as European Americans, who have fewer copies of the gene, according to a study funded by the National Institute of Allergy and Infectious Diseases (NIAID), part of the National Institutes of Health (NIH). The findings help to explain why some people are more prone to HIV/AIDS than others.