Telomerase gene therapy is considered in some quarters to be a viable treatment for aging. Telomeres are the caps of repeated DNA sequences at the ends of chromosomes. They are an important part of the mechanism limiting the number of times that somatic cells in the body can divide, the Hayflick limit. A little telomere length is lost with each cell division, and short telomeres trigger cellular senescence or programmed cell death, halting replication. Stem cell populations use telomerase to lengthen their telomeres and thus self-renew to provide a continual supply of new somatic daughter cells with long telomeres to replace those lost to the Hayflick limit. Average telomere length is reduced over the course of aging because stem cell function declines.
This division between a few privileged stem cells and the vast majority of limited somatic cells is the way in which higher forms of life have evolved to reduce the risk of cancer. Somatic cells largely do not last long enough to develop mutational damage sufficient to become cancerous. When cancer does occur, most cancer lineages use expression of telomerase in order to lengthen their telomeres,
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