I am pleasantly surprised that you have heard of Myhre. At the most recent Zoom meeting on Myhre research it was revealed they are working on a process that would transfer genetic information from one parent's chromosome to the other. If they can do that for my grandson, it will be a game changer. It won't reverse the biochemical damage that has been done but it will prevent further damage. I have got my fingers crossed.

I know that he has Myhre syndrome. That’s why I asked you how is his receptive speech, In order to be able to apply the suggestions I gave with the hope of some success.
I’m sure you are more proficient in this syndrome than I am, but my knowledge of it is one of the symptoms is intellectual & behavioral issues, in addition to speech. From my understanding the severity of the syndrome seems to vary by individual, just as autism does. Again you said he understands what you tell him…which is a complete asset in trying to improve the behavior. I’m of the belief that it can’t hurt to try anything & everything. I replied to your question & continued to try to help in thinking of my own parents & how difficult my children’s diagnosis’s has been on them. I hope you find a good therapist. I wish you the best!

He has already had an echocardiogram and had his DNA sequenced.

Our grandson is one of less than 300 in America with Myhre Syndrome, a very rare genetic disease.

I can tell you what has worked for us & my experience.
Hopefully you can use some of this info to mold to your family.
Typically autism is also associated with other diagnosis. My kids have asd, but they also have other issues.
Their issues are somewhat different from each other, but between them both there’s also; adhd, anxiety, depression, ocd, pica, trichotillomania, poor self worth, food, sensory etc.
I do think it’s great that his mother is seeing someone to help her with this emotionally.
My kids are both verbal, now, but still have pragmatic speech issues. When a child cannot speak or effectively say what’s wrong that leads to frustration, meltdowns & anger.
My experience from ABA is they use a reward system, something the child really likes (a food item or toy) in order to get compliance & teach him/her.

His home & yours-when he’s there- has to be set up the same for consistency across all areas. We used a positive reinforcement plan to promote the behaviors we wanted & incentives for the kids to receive rewards when desired behaviors were achieved. It can simply be a poster board with 4-5 behaviors you’d like to see from him & when he’s done what you’ve asked, he gets rewarded with something that he loves. A lot of verbal praise will reinforce the desired behaviors. For my oldest child (now 20) we learned & taught her sign language for her basic needs so we could communicate with her before she was able to speak.