Sounds like a lot of your ds problems could potentially be gluten related (sleep, stiffness, ulcers..), my ds was mega clumsy and very stiff in posture/unbalanced, but has dramatically improved on gf diet, I put him on in desperation as had felt I was losing him slowly - and never looked back. I know if we lapsed with diet he would lapse too.
Once my ds started improving, I only wanted to confirm that there was a reason, he did have a gene test (done by a neuro) and came out as gluten sensitive ie not celiac, so it wasn't a coincidence. No other treatment needed, just diet, although I have done various tests to check for any metabolic/absorption abnormalities and found various deficiencies that I have been working through.
Just search for neurology/gluten, you will be amazed how much proper research is around - although there are very few GPs/drs who are aware of this possible link, mine weren't.
You now have to be a member of pubmed to see research papers, but some are linked here, check out the Neurological Manifestations of gluten sensitivity.
Also, leaky gut can also be a result of gluten damage, silverfrog is right. Severe neuro damage can be irreperable, but if he does respond to diet, there is a chance that some of the enzymes/hormones might correct themselves.
Write to your neuro and try and get copies of the scans across to him.