An individual's DNA determines the timing when HIV turns into AIDS, according to a new study.

In the study, Stephen O'Brien from the National Cancer Institute in Frederick, Maryland, and colleagues found that some variations in the DNA in mitochondria, the parts of cells that generate energy, seem to make AIDS develop twice as fast as others.

For the study, they examined data from five long-term studies tracking a total of 1833 people with HIV during the 1980s and early 1990s.

This was before antiretroviral therapy (HAART) was commonly used, so the team could follow the disease's development without intervention.

By examining the time it took for the subjects to develop AIDS-related diseases and linking it to their genetic information, the researchers found that some mitochondrial DNA genotypes are linked to rapid development of AIDS.

For example, subjects with specific sets of variations known as U5a1 and J haplogroups progressed to AIDS at twice the average rate of the studied population. On contrary, people with the H3 haplogroup progressed less than twice as slowly.

This supports existing theories that mitochondria are implicated in the progression of HIV/AIDS.

The virus kills immune cells by triggering cell suicide, which appears to happen more easily in cells with mitochondria that generate less energy.

"Having less energy available seems to exacerbate the effects of the disease," said co-author Sher Hendrickson.