(From the Telegraph). Our ability to hear depends on hair cells in the inner ear: "Normally, humans are born with about 50,000 hair cells but since they do not regenerate, the steady loss that can accompany ageing produces significant hearing deterioration in about a third of the population by the age of 70." Fortunately, scientists have demonstrated - in guinea pigs at least - that gene therapy can be used to coax these hair cells into growing once more. "Now Dr Raphael and colleagues have shown that a type of cold virus, called an adenovirus, can be used to implant a gene, Atoh1, and induce new hair cells to grow in the cochleas of deafened guinea pigs. The gene helps guide development of the ear. In a second study, another American has found that the deletion of a specific gene permits the growth of new hair cells in the inner ear."