One reason that cells break down bone is that in old age they make less of a protein called TERT. In 2012, researchers at the Spanish National Cancer Research Centre coaxed old mice to make extra TERT by giving them an extra copy of the gene. Their osteoporosis reversed, and their bones strengthened. It's conceivable that doctors could use CRISPR gene therapy to treat people as well. CRISPR molecules would home in on the TERT gene in bone cells and edit it. The gene would behave as it did when the patients were younger, strengthening their bones. But gene therapy for TERT could do a lot of other kinds of good, too. The Spanish researchers who tried it out on mice found that it also reversed aging in their muscles, their brains, and their blood. It extended the life span of old mice by 13 percent. When the scientists treated younger mice with TERT gene therapy, the animals lived 24 percent longer.