Indications of changed amino acid homeostasis in untreated and treated PKU.

Amino acid patterns were investigated in children with untreated and treated phenylketonuria (PKU) and compared with a hospitalized paediatric control group. Correlation ratios, i.e. the ratio between the number of statistically significant correlations between pairs of amino acids, were calculated and found to be 0.125, 0.331 and 0.35 in the three groups. Link ratios, i.e. the frequency of statistically significant correlations between a particular amino acid and other amino acids, varied between 0.00 and 0.18, 0.06 and 0.56, and 0.18 and 0.59 in the same groups. Link ratios for especially isoleucine, histidine and arginine were decreased in treated PKU compared to the control group. A reverse nonlinear relationship was established between decreased plasma phenylalanine induced by dietary treatment and increased threonine in plasma. These findings indicate that amino acid homeostasis is disturbed in untreated PKU and not fully normalized in treated patients. The clinical relevance of the findings is unknown.