Blaine at The Genetic Geneologist (www.thegeneticgenealogist.com/2010/01/07/personalized-genomics-a-very-personal-post/) has posted a very personal story about his genotype at three loci for risk of type 2 diabetes. The SNPs are rs5219 in KCNJ11, rs1801282 in PPARG and rs7903146 in TCF7L2. With risk alleles for all six alleles, his risk, as calculated by the services he used, is significantly elevated.
A genotype is, as he writes, merely a suggestion of a possible future outcome. Lifestyle intervention before disease onset is clearly warranted. We have shown, for example, that variants at TCF7L2 associate with postprandial lipemia (after-meal levels of blood lipids) but are modulated by PUFA (polyunsaturated fatty acid) intake. See www.ncbi.nlm.nih.gov/pubmed/19141698, where my colleagues wrote "high (n-6) PUFA intakes (> or = 6.62% of energy intake) were associated with atherogenic dyslipidemia in carriers of the minor T allele at the TCF7L2 rs7903146 SNP and may predispose them to MetS, diabetes, and cardiovascular disease." Links between dyslipidemia and T2DM are well established.
In other words, the interplay between environment and genome is an important consideration that is often overlooked.