Plasma zinc, copper, and erythrocyte superoxide dismutase in children with phenylketonuria

Children with phenylketonuria (PKU) are treated with semisynthetic diets restricted in phenylalanine (PHE). The formulae must supply those trace elements and vitamins that are usually supplied by whole protein foods. We studied the effects of phenylalaline restricted diets in 42 children with PKU (P) and 31 normal (N) children, aged 1–12 y, divided into two groups (below and above 7 y). Plasma zinc and copper were analyzed by means of atomic spectrophotometry, and superoxide dismutase (CuZnSOD) activity was measured in erythrocytes, through NBT inhibition and its profile, as determined by isoelectric focalization. Plasma zinc of PKU children ≥7 years old was significantly lower than that in the control group (17 μmol/L versus 20 μmol/L) but still within the normal range; in children <7 years no substantial differences were found between the two groups. Plasma copper was not statistically different between PKU and normal children. Qualitative activity of CuZnSOD presented the same electrophoretic profile in both normal and PKU. Quantitative activity was not different in both P (1210 U/g Hb <7 versus 1328 U/g hemoglobin (Hb) ≥7) and N (1675 U/g Hb <7 versus 1367 U/g Hb ≥ 7). We concluded that children with PKU presented normal mean levels of zinc and copper, with preserved function, measured by enzyme activity.