Allison,
Interesting, that this kid has both Phenylpyruvic and 4-hydroxyphenyllactic high. There appears to be an issue in both phenyalanine and potentially tyrosine metabolism. I like the idea of the BH4 at 2.5mg BID and your other recommendations too. I would make sure to have him on a multivitamin/multimineral too like Spectrum-Mate from New Beginnings.
I would do a MycoTOX Profile on this guy as well. Ochratoxin is a known Phenylalanine hydroxylase inhibitor.
Sincerely,
Dr. Woeller