More than 400 mutations were found in the healthy white blood cells of a 115-year-old woman, according to a new study that may advance what is known about limits of the human life span.
Genetic mutations have been linked to diseases such as cancer, but these findings suggest that mutations in white blood cells are largely harmless over a lifetime, the researchers said.
Blood is continually replenished by hematopoietic (meaning "to make blood") stem cells that are inside the bone marrow and divide to produce different types of blood cells.
Cell division can lead to genetic mutations and hundreds of mutations have been found in patients with blood cancers. However, little was known about white blood cells and mutations.
The woman in the study - whose name was not revealed - was the oldest person in the world when she died in 2005. She is thought to be the oldest person ever to donate her body to science. The hundreds of mutations identified in her white blood cells appeared to be tolerated by the body and did not cause disease.
The researchers also found possible new insight into the limits of human longevity, according to the authors of the study published online April 23 in the journal Genome Research.
"To our great surprise we found that, at the time of her death, the peripheral blood was derived from only two active hematopoietic stem cells (in contrast to an estimated 1,300 simultaneously active stem cells), which were related to each other," lead author Dr. Henne Holstege said in a journal news release.
The researchers also found that the woman's white blood cells' telomeres were extremely short. Telomeres, which are at the ends of chromosomes and protect them from damage, get a bit shorter each time a cell divides.
"Because these blood cells had extremely short telomeres, we speculate that most hematopoietic stem cells may have died from 'stem cell exhaustion,' reaching the upper limit of stem cell divisions," Holstege said.
Further research is needed to learn whether such stem cell exhaustion is a cause of death in extremely old people.