Is it legal for an employer to ask if you have Asperger's syndrome?

My brother was interviewed for a promotion at work. He is a very nervous guy and exhibits many Aspergers-like characteristics, but has not been officially diagnosed (a touchy subject in my family). He is normally very high-functioning and performs his job well, despite being a little “different”.

During the interview, the manager flat-out asked him if he has Asperger’s (my brother never brought it up or even hinted at it). Hearing those words come out of his boss’s mouth caused my already-nervous brother to panic and have an embarrassed mini-meltdown. He was eventually told to go home because he could not calm down (was lashing out at people asking why he was upset, etc).

Did the manager have the right to ask him that?