I agree that anyone with ASD should try a diet free of gluten, casein, AND soy as the first treatment. Harumi Jyanouchi's study showed 91% (yes, 91%!!) of kids wiht autism got inflammation responses in their brains from those 3 ingredients. If you have not tried eliminating these foods from the child's diet yet, that would be my reccommended first step. My son became potty trained, his constipation stopped, he began sleeping all night and he stopped flapping his hands and staring at spinning objects when I put him on the diet.
For more info on Feingold-like stuff, you don't have to buy their program, you can get very good info on phenols and salicilates at Dana's View. Go to google, search this exact phrase "dana's view phenols". My son had behavior ups and downs- hyperactivity, agression, etc and that completely stopped when I FURTHER removed all high phenol and Salicilate foods form his diet. Apples, berries, corn syrup, and food colorings were 3 of the very worst offenders. I can re-test my theory any day- it just takes about 1/2 cuup of berries and the dark circles will return to his eyes, his ears will turn red, and his humming will return- or aggression, or both. Interesting note- many of these phenol sensitive kids can NOT tolerate B-6 either (like my son).