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Phenylketonuria is an autosomal recessive disease caused by mutations in the gene coding for phenylalanine hydroxylase (chromosome 12q).
Phenylalanine hydroxylase deficiency produces elevated phenylalanine concentrations in plasma, CSF, and urine as a direct result of the inability to convert phenylalanine to tyrosine. Tyrosine concentrations are low relative to the elevated phenylalanine concentrations, but are usually within the normal range because of sufficient dietary tyrosine intake. When hydroxylation of phenylalanine is blocked, there is increased transamination of phenylalanine to phenylpyruvic acid, which is readily excreted in urine.
All PKU patients must adhere to a special diet low in Phe for optimal brain development. "Diet for life" has become the standard recommended by most experts. The diet requires severely restricting or eliminating foods high in Phe, such as meat, chicken, fish, eggs, nuts, cheese, legumes, milk and other dairy products. Starchy foods, such as potatoes, bread, pasta, and corn, must be monitored. Infants may still be breastfed to provide all of the benefits of breastmilk, but the quantity must also be monitored and supplementation for missing nutrients will be required. The sweetener aspartame, present in many diet foods and soft drinks, must also be avoided, as aspartame contains two amino acids: phenylalanine and aspartic acid.
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