Pfft, my dd1 (5.5) has a button phobia. She's had it since she was tiny (noticed her freaking out about buttony shirts at about 18 months) and its not gone away - it really worried me at first, but is now an ok part of every day life.
I did lots of research (its got a name!) and found several adult friends who had the same thing - they gave me loads of tips on how to cope, and what NOT to do. I've also met others with kids with the same phobia, its not that uncommon.
I did also find a very highbrown American psychiatriatists site, which explained the latest theory on phobias as being mostly genetic - though what the phobia fixes on, ie buttons, birds, spiders etc, can change from generation to generation. Basically, primal fears, hardwired into the brain, that come out in different ways.
We've always told dd 'oh, ok, thats how you feel about buttons, not everyone feels that way but we're all different - thats just how you feel, its ok'. She's far less freaked out by them now, but still wo'nt wear them on her upper body - but she will play with them, do up mine, wear them on jeans. I feel pretty relaxed about it now, and school are very understanding (quite rightly, IMO).
Do feel free to CAT me if you like - I'm away from Friday for 3 weeks, but am happy to pass on anything else that might help!
And no, never went to GP.