Mutation and the Aging Process: Mutant Frequency at the HPRT Gene Locus as a Function of Age in Humans

Aging is a complex, biological process that is contributed to by intrinsic (genetic) and extrinsic (nutrition, infectious agents, xenobiotic exposure, etc.) factors (1 ). Several decades ago it was first proposed that instabilities in the organization and expression of the genetic material was likely to be involved in the aging process (reviewed in ref. 2 ). Indeed, since that time much experimental evidence has been published that details increases in DNA damage (3 –8 ) and mutation (8 , 9 –15 ) in various cells and tissues with age in humans.