I know some people who would find it just as offensive that their status was regarded as a "disorder", so I don't know that there's any universally accepted way of describing it. As for "official medical terms", have that discussion with some feminists about http://en.wikipedia.org/wiki/F...
Some goes for gender dysphoria. If dysphoria is defined as "a state of unease or generalized dissatisfaction with life", I'm not sure I'd want that label either.
otoh I'd suggest "gender assignment" is a stupid term since it implies a decision on behalf of the parent/doctors/etc and tends to the provocative.
In any case, I don't mean it to be dismissive or invalidating in general, even if there are some people that are either mistaken or attention seeking in this area, as in every other area of human experience.