Danger of high-protein dietary supplements to persons with hyperphenylalaninaemia.

A 16-year-old adolescent with mild hyperphenylalaninaemia was given a high-protein 'body building' supplement twice daily, causing headaches, decreased school performance and mild depression. All symptoms disappeared after cessation of the supplement. The phenylalanine hydroxylase mutation H170D/IVS1nt5G>T was found to be responsive to tetrahydrobiopterin with significant decrease in blood phenylalanine concentration and increase in tyrosine blood content. A brain phenylalanine level of 0.5 mmol/L was initially documented, which decreased to the normal carrier range of 0.2 mmol/L within one month of discontinuance of the protein supplement. At present, the patient is on a normal diet without phenylalanine restriction.