HM, my ds was dx when little with a progressive neuro deterioration with "once started there is nothing you can do". For 10 years I really thought that was the end and he was getting progressively worse. When internet came about I was looking everywhere for anything that might help, he had various tests (ALD etc) but no clues and was still slipping.
Via another forum I found out that in some cases gluten affects neurology, well, I just had to try it.
Before diet, his shoe soles were drastically assymetrically worn, but it was osteo who pointed out that we need to look at the whole posture rather than just doing soles/splints. He had a few sessions when already on the diet as I wanted to kick start him in various areas when I realised he started to improve. The soles progressively changed and the current are almost symmetrical, although one of his feet is ever so slighthly curling to the inside, I don't think it can be fixed now. It was also noticeable, when we went gluten-free how he started uncurling his fingers, stretching them outwards, for me it was like a miracle.
Hard to know if it would work for someone born(?) with CP. Our neuro said that in his experience of gluten sensitivity cases, once gluten is out of the way, he will start absorbing everything better, but 2 years on I did a hair test for him and he was still low in Zn, Mg and high in Cu which is toxic. Was also advised to add B vits. The key was to do it selectively, rather than multivit.
The best bit is that I feel we are in control of it all as it's just food and vits and by golly, I do know when he has been glutened as his speech and reactions drop and take a few days to recover. We just do an occasional vitamin/omega capsule from time to time, maybe 2-3 times a week and not in mega doses and he is def not getting worse overall in any area if we make sure we stick to diet.