My sister has gout and Downs as well. She does not take anything for it. I can say the same thing the other poster said:
It is important to note as mentioned that almost anyone that gets on allopurinol will immediately have a gout attack after because the medication is flushing the UA and that will cause it to accumulate in joints at first, so that is completely normal.
I also agree you should perhaps see a rheumatologist that specializes in gout first before your son takes it long term. If anyone has the best medical advice it would likely be that person.
I have gout and nobody else in my family does except my sister. I tell my dad all the time to adjust her eating habits as they are pretty bad, but she isn’t one to take kindly to not having a fast food burger. She also hates the taste of water so always has to be drinking something with flavor. I’m sure you know how the stubborness works there. But the more you can make them adhere to a better diet is probably the best initial route to go and see how that helps. The one benefit is most likely alcohol is not part of the diet and that’s a primary culprit for most people, so even limiting some meat and soft drinks here and there could really make a big difference. The only problem with all this, is the results will be slower to realize. I would recommend getting a blood test initially to see UA levels, try 3 months of a new diet even if flare ups happen, and then do another UA test to see if the UA level dropped any whatsoever. If it did even a little bit, do it another 3 months and see how the progress goes. If you can get your son to change his diet to more water intake and less meat, etc. then perhaps in a year your problems are manageable drug-free.