http://news.sciencemag.org/biology/2015/01/environment-more-genetics-shapes-immune-systemJust wanted to plop this here since no doubt a lot of us are going to be hearing about this one. The media has picked it up, and is (as usual) twisting and extrapolating in ways that are not entirely warranted.
The immune functions that were assessed in this twin study were
not necessarily aimed at atopic disease, and mostly focused on the b-cell and
other t-cell type responses.
There are crossover points, to be sure-- and there was some analysis of autoimmune and atopic conditions, but basically there isn't much that is news with the latter.
Even identical twins are not necessarily sharing "allergy to milk" or "cat allergy" just "tendency to develop allergies to stuff."