My only concern (echoed by many anti-GMO'ers, of which I don't consider myself a part) is of horizontal gene transmission[0[, primarily because I have no training or experience in the subject matter. But it's not enough of a concern to me to fight against GMO, because there are better fights to be fought! I simply wish I knew more.
Here is the link on the study (haven't had time to evaluate the test design yet): http://www.journalofanimalscience.org/content/early/2014/08/...
I recommend this article [0] by Mark Lynas [1] that explains the arguments that convinced him to go from a vocal anti-GMO activist to, what he calls, a pro-science environmentalist. (I think the hip term now is "eco-modernist"). From the article:
What happened between 1995 and now that made me not only change my mind but come here and admit it? Well, the answer is fairly simple: I discovered science, and in the process I hope I became a better environmentalist.
[0] http://thebreakthrough.org/index.php/programs/conservation-a...