You may possess a genetic mutation. Most people would probably be aghast to
learn that one of their genes is malformed. But before you start asking,
"What does that mean? Will it make me sick someday? Will I pass it on to my
children?" bear in mind that a mutation of the CCR5 gene -- called "delta
32" in its mutated form -- has no adverse effect on humans. In fact,
possessing delta 32 could save your life, and the lives of your children.

"It's highly unusual," says Dr. Stephen J. O'Brien of the National
Institutes of Health in Washington D.C. "Most genes, if you knock them out,
cause serious diseases like cystic fibrosis or sickle cell anemia or
diabetes. But CCR5-delta32 is rather innocuous to its carriers. The reason
seems to be that the normal function of CCR5 is redundant in our genes; that
several other genes can perform the same function."

"The non-mutated form is what's called a chemokine receptor," he says.
Chemokines are protein distress calls released by an injured region of your
body. "The normal function of the CCR5 gene is to act as a retriever of the
chemokine distress signal from these bruises, which will then be alleviated
by the chemokines."

This may not sound exciting, but delta 32 is a powerful mistake. HIV, the
virus that causes AIDS, attacks the human immune system, infecting the white
blood cells sent to destroy it. The delta 32 mutation, however, effectively
blocks the crucial gateway into human cells the virus needs. In the case of
Steve Crohn, whose partner was the fifth person to die from AIDS, possessing
the CCR5 mutation has prevented him from contracting the virus.

O'Brien explains further, "In order to have total resistance to HIV, you
have to carry two doses of the mutated gene -- one from each parent. If you
get only one dose, you will not be resistant to infection. However, you may
be able to delay the onset of HIV once you become infected. That's because,
in patients with one copy of the mutation, the amount of 'portals' or
'doorways' that HIV can use is reduced by about 50 percent. That slows down
virus replication, which is the most important factor in AIDS progression."

O'Brien's work on AIDS led him to another disease that delta 32 could
prevent, the plague. "They both, upon entering the body, infect the
macrophages, which are the first line of defense against bacterial
infections," he says. "Over the course of evolution, many bugs and pathogens
have become extinct because the body learned how to defend itself against
them. So the ones that are around today, like HIV and the plague, are pretty
savvy -- HIV, for example, specifically attacks and kills the very cells
that are designed to kill it. Both these pathogens have developed very
clever ways around our immunological defenses."

The results of the Eyam study suggest that delta 32 may have helped save
Europe from the bubonic plague pandemic. It seems logical, then, that this
could be confirmed by an experiment in which the plague bacterium is
injected into the cells of someone possessing the delta 32 mutation. "We
have attempted to design experiments that allow us to expose the plague to
the lymphocytes of different people, including Steve Crohn," O'Brien says.
"But so far we haven't been able to design that kind of experiment ... to do
that experiment, you would need to isolate that particular kind of cell. You
would need to isolate the exact strain of the plague, and you would need to
expose them together."

Nevertheless, delta 32 seems to be a formidable defense the human body has
developed in response to ages of pathogenic exposure. And though we may just
be getting acquainted with it, delta 32 has been protecting humans for ages.
O'Brien suspects the mutation has been around since long before the Black
Death. "There have been human remains dug up from graves in Scandinavia --  
bodies 3,000 and 4,000 years old -- in which they actually found the
mutation, through DNA typing. So there are all kinds of pieces in this
puzzle that are coming together."