Scientists who study human evolution have long puzzled over why African Pygmies are so short. It is one of the most visible examples of human diversity, with Pygmy males standing 4-foot-11 on average, while some of their neighboring ethnic groups are tall. Many biologists have assumed there must be some evolutionary advantage to their short stature -- perhaps that they better maneuvered through the forest or they survived on less food.
A University of Pennsylvania team went looking for an answer in DNA. Penn geneticist Sarah Tishkoff, Coriell Institute researcher Joseph Jarvis and colleagues reported that they found many differences between Pygmy DNA and that from neighboring Bantus, but none that would alone account for their stature, or tie it to an evolutionary benefit. They were left wondering whether genetic variants spread in the Pygmy populations because they got stuck to mutations that had other benefits.
About 40,000 Pygmies live in Africa, mostly in Cameroon, said Alain Froment, an anthropologist and medical doctor who collaborated on the study published in the journal PLoS Genetics. As a group, Pygmies are ancient, having branched off from other Africans 60,000 to 70,000 years ago. At that time, modern humans had yet to leave Africa and Neanderthals and other archaic humans populated Europe and Asia. For eons, they were isolated, but over the last 4,000 years they have periodically mixed with the Bantu, Tishkoff said.
Tishkoff said one of the more interesting genes that might be connected is called CISH. It's connected to immune proteins called cytokines, which can help fight off infections and affect the body's ability to react to human growth hormone. Tishkoff said it's possible that there's no advantage at all to being short, but that their shortness was a side effect of some beneficial mutation that helped them better fight diseases.
HIV patients given gene therapy more than a decade ago are healthy and the altered DNA they received remains stable, said a study in the journal Science Translational Medicine.
All except two of 43 people treated with altered versions of their own infection-fighting T cells were healthy as many as 11 years later, said Bruce Levine, a study author and researcher at the University of Pennsylvania.
Previous uses of gene therapy in experiments have suggested that leukemia caused by the viruses that transfer the genes to the cells might be a risk. The Food and Drug Administration required the patients be followed for 15 years to see if any late-developing side- effects, such as cancer, might arise.