I think the parent is spot on. Just some background in brief: Single nucleotide polymorphisms (SNP in the singular) are single base changes in the genome. Give

I think the parent is spot on. Just some background in brief: Single nucleotide polymorphisms (SNP in the singular) are single base changes in the genome. Given the size of the genome (approximately 3 billion bases), the mutational rate, and the time since all modern human populations diverged from a single ancestral group (sorry, no number off the top of my head) we should expect that each position has mutated no more than once. So, for the most part SNPs come in two flavors, a minor allele and a major allele. If the SNP is associated with disease, one allele is called the risk allele, while the other is the protective. Down to business. For a SNP and a disease, we can compute the odds ratio or relative risk (there is a difference) for that SNP. Suppose you have the risk allele, the relative risk is 2, and the frequency of disease is 1% -- congratulations, you have a nominal 2% chance of developing the disease. Alright, onto the problems: For most complex diseases, this doesn't help us in the slightest and is non-informative. There are a lot of markers, these diseases are rare, genetic risk might well be subsumed by environmental effects. (Good rule of thumb: Don't smoke cigarettes, don't be obese. Eat your vegetables. I'm a scientist, not a doctor.) If you test someone, you'll invariably get a pile of risk alleles for some disease, just because there are a lot of diseases and a lot of SNPs. This will invariably cause distress in at least some people. The harm done to the subjects would clearly exceeds the benefits to them. Given the study design there's no reasonable way to obtain informed consent from the subjects if they're to be informed of the results. Without informed consent, you can't gather the data in the first place.