--apparently have received the mutation that allows them to process wheat products well, but many people have not. In addition, the genetic modification of wheat (and to a lesser extent, barley and rye, other gluten containing grains) over the last hundred years or so may be contributing to the numerical rise in cases of celiac and gluten sensitivity--gliadin, the protein reacted to, is certainly present in higher proportions in "modern" wheat.

Not to disparage "Wheat Belly", but, in my opinion, the best source of vetted scientific information on the whole gluten area, including non-gastrointestinal manifestations of gluten difficulties, is still jcc's The Gluten File, the most massive database on the subject available, and linkable right through Neurotalk:

http://neurotalk.psychcentral.com/thread1872.html

jcc continues to update this on a regular basis, whenever new reserch material comes up. One can literally spend days here going from one article to another piecing together the possible manifestations of gluten sensitivity or celiac, diagnostic choices/problems, etc.