""To the [New York Times] Editor: Re My Genome, Myself: Seeking Clues in DNA (“The DNA Age” series, front page, Nov. 17, 2007): Wanting to know more about ourselves is both a strength and a hazard. The lure of genetic data can be compelling but misleading, for no list of tiny variants in one’s genetic code can reliably predict one’s future regarding cancer, heart attacks or diabetes, let alone I.Q., addiction or gullibility. Amy Harmon’s humorous account of her own genome search may still leave many readers willing to send off a little saliva — and a big check — to a genome company. Those companies are selling only a fragment of your identity. Knowing that you have this or that disease-associated SNP in your genes tells you very little or helps only with rare diseases. What causes the SNP (single nucleotide polymorphism) to be expressed, to spring into action or to remain dormant? Why can identical twins, with genomes alike down to the last SNP, develop different diseases? What if you smoke, toil for years in a high-stress job or live in a polluted neighborhood? Predispositions are just the beginning. Your future depends on much more than your genetic code. Ms. Harmon would have done better to spend her money on a good gym, and The Times would serve us better by emphasizing the limits of genetic knowledge."