I don’t currently put much stock in disease risk estimates given by personal genomics firms. My pedigree is pretty large, so I already have a lot of information on the table (though the demographic transition across the generations in Bangladesh is pretty evident in my own family). Family information is currently much more useful in estimating relative risks than GWAS for most diseases (as it is for quantitative traits like height and I.Q.) If a friend wants to get genotyped to better understand their disease risks, unless they’re rolling in money, I generally advise them to hold off.
But the returns on personal genomics in this area has nowhere to go but up, so we should understand exactly what the odds for disease risk we are getting from firms like 23andMe now, because we will have to at some point in the future. Carl Anderson at Genomes Unzipped has the first post of two up on this issue. The plot I’ve taken from the post shows the dependence of relative risk as a function of number of risk loci included. Remember that the average risk for the trait, ulcerative colitis, is rather low, at ~1%. So even if you have a 2.5 × greater than average risk…I wouldn’t stress out too much.
Note that the relatively marginal predictive value of personal genomics currently means that worries about this sort of thing making people uninsurable are probably not grounded in reality. The family disease history is much more actionable when estimating your premium, or whether they should underwrite you in the first place.