Thanks for helping with this, rumpled. I made out the word "syndrome" on the paper, but I could not make out what the preceding word was.
Enzy
According to what you posted, he was diagnosed with Angelman Syndrome - which is a genetic disorder. There is no cure.
From the symptoms you describe, that seems to fit. Other than physical therapy and other care that is similar, I don't really have any other ideas.
First, I am not a doctor. Just an average American citizen. If I'm reading the hospital report correctly, this child had an organic acid test, and was high in ammonia?
Was the child given anything to take, to detoxify his system of the ammonia? At least some vitamin B6, glutamic acid (important for removing ammonia from the brain), magnesium, aspartic acid, arginine or alpha-ketoglutarate?
Is the child suffering from malnutrition? A metabolic disease specialist might be able to give you some help. In the meantime, physical therapy is important. For instance, toe walking is often from shortened calf muscles, caused by vitamin and mineral deficiencies, and other causes. Gently forcing the toes back and heels down can help with this over time.
This child needs to see a specialist, and if he has ammonia toxicity, that needs to be addressed immediately.