Invoke the Masters of Universal Medicine: Archangel Raphael, Hermes Trismegistus, Paracelsus, Galen, the Angel Adonai, etc. You can write a letter to the temple of Alden in order to request his healing.
The best thing you can do for him is to pray, and to have the courage to accept the things that you may not necessarily be able to change. Autism of the spectrum you've mentioned is very serious karma, and you must always place persons in such a condition within the hands of الله Allah, the Being.
Therefore, be at peace, and your peace will irradiate strength and serenity to your brother.
For thirty years I sought God. But when I looked carefully I found that in reality God was the seeker and I the sought. -Bayazid al-Bastami