just for another data point, I tested negative to celiac and I don't the most common genes, but I'd read some of Dr H's research and since I had lots of balance problems in addition to the gastro stuff, I was determined to go gluten free even without a diagnosis. It probably took about 3 months before I noticed any improvment in the neuro stuff (yet only 3 days for the gastro improvements) and maybe 6-8 months before it was heaps better. If I get glutened one off, I don't have any neuro issues but if it's a tiny amount over a few days (as has happened when I was travelling and had less control over my food) my balance goes really wonky again. Since I'm not used to it, it feels even worse than before.
Best wishes to your brother Gatita, it sounds very scary :-(