As many has pave said on the other thread a bout ASD/ADHD and gifted: if it's impairing his functioning, treat it, rather than worry about the correct diagnosis.
I would say that with a HG kid,anxiety is pretty useless as a defining symptom! Have you looked into sensory processing disorder - t shirt chewing, jumping pacing nail biting, skin picking...a sensory diet might help alleviate all this. Um, sensory issues are correlated with anxiety.... You may want to check out sensational kids and the out of synch kid, see whether it rings a bell.
