[asdff]

Gene by environment interactions are super important for understanding how genotypes affect fitness in context. Change your environment to the open ocean instead of on land, for example, and you can readily see how your genes now hurt your chances for survival instead of improve them.

That being said, there's a lot to the genetic compotent of disease risk beyond just changes to the sequence of protein coding genes. How much protein that gene produces can be affected by a number of factors, such as the presence of singe nucleotide polymorphisms (changes to one site in the DNA) that may be well outside the gene region in the genome, but are a binding region for a transcription factor or an enhancer that drives expression of that gene and therefore dramatically lowers (or increases) the protein produced. You can also have epigenetic changes that similarly effect gene expression, but these are not reflected anywhere in the genomic sequence since these represent changes to the proteins that package DNA in the nucleus, not to the DNA itself.