This study examines the effect of tetrahydrobiopterin (Kuvan) and Large Neutral Amino Acid
(LNAA) therapy on melatonin and dopamine levels in individuals with Phenylketonuria (PKU).
The investigators hypothesize that Kuvan therapy will improve melatonin secretion and urine
dopamine levels to some extent. However significantly greater responses in melatonin and
dopamine secretions may be observed with combined treatment with Kuvan and supplementation of
LNAA.