In that telomeres are the endcaps on chromosomes, and telomeric shortening is thought to govern the number of times a cell can divide, telomeric replication is governed by an enzyme, telomerase. Gil Atzmon, from Albert Einstein College of Medicine (New York, USA), and colleagues studied Ashkenazi Jews, a population group that generally lives well into their 90s and beyond, in a generally healthy condition.  The researchers found that participants who have lived to a very old age have inherited mutant genes that make their telomerase-making system extra active and able to maintain telomere length more effectively. For the most part, these people were spared age-related diseases such as cardiovascular disease and diabetes, which cause most deaths among elderly people. The team observes that: "As we suspected, humans of exceptional longevity are better able to maintain the length of their telomeres.  [T]hey owe their longevity, at least in part, to advantageous variants of genes involved in telomere maintenance."