Phenylalanine metabolism disorders effects

Paddon-Jones et al. reported optimal protein synthesis when dietary protein was provided three times per day compared with the same total amount of protein given in various amounts [26, 29]. In patients with PKU, providing amino acid-based medical food throughout the day compared to a single dose of similar protein equivalents had a positive effect on protein synthesis [30]. A positive effect on plasma phenylalanine concentrations was also reported [30]. For patients with a metabolic disorder, providing medical food along with limited whole protein foods is most beneficial to optimize synthesis. 

Some inherited metabolic disorders are extremely damaging while the effects of others are so mild that they can hardly be called diseases. For example, alkaptonurics are usually quite healthy although in later life they are prone to a particular form of arthritis. Similarly the conditions of fructosuria and pentosuria, in which fructose and pentose sugars respectively appear in the urine, have no pathological consequences. At the other end of the scale is phenylketonuria in which the enzyme phenylalanine hydroxylase, which is responsible for converting phenylalanine to tyrosine, is lacking. In this condition phenylpyruvic acid and other intermediate products of phenylalanine metabolism accumulate in the blood and tissues and are so injurious to the central nervous system that, although physical development is essentially normal, there is severe mental retardation. 

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