Thank you for your query.
Though you have given a detailed description of the growth issues with your son you have not mentioned whether growth hormone investigations were done on him and what were the results. In my opinion he should be investigated for growth hormone deficiency
and treated appropriated. You may continue Guanfacine
for his ADHD
but give glutamine supplements only under medical supervision after it has been confirmed that he has an insufficiency of GABA-glutamine-glutamate cycle.
I hope I have responded to your query to your satisfaction.
Wishing your son all the best.