Selenium status in infants and children with phenylketonuria and in maternal phenylketonuria

The selenium status was investigated in 87 patients of the German Collaborative Study of Phenylketonuria (PKU) (mean age 9.7 years). The selenium values and glutathione peroxidase activity in plasma and erythrocytes were negatively correlated to the quality of dietary management (mean plasma phenylalanine value). Despite a low selenium state, the children showed no clinical sign of deficiency and almost all biochemical parameters checked were normal. In the low selenium state thyroxine values are increased and decline during selenium supplementation, whereas tri-iodothyronine and thyroid stimulating hormone levels remain unchanged. The reduction in glutathione peroxidase activity in plasma was more pronounced than in the erythrocytes pointing to a different availability of both enzymes for selenium. In addition we estimated the selenium status in 29 women with PKU during pregnancy. In 32 healthy pregnant women we observed a decrease in plasma selenium values and the glutathione peroxidase activity in the third trimester, whereas the erythrocyte glutathione peroxidase activity remained stable. In contrast to the healthy women we found in the PKU group a steady decrease of all selenium parameters tested during the whole pregnancy. During the long-term low-dose selenium supplementation in PKU children the glutathione peroxidase activity of plasma and erythrocytes increased. They reached a similar plateau after the application of inorganic or organic selenium compounds. In contrast the selenium values of plasma and whole blood showed only a plateau after the application of sodium selenite. The supplementation with low doses of selenium in the form of selenomethionine increased the plasma and whole blood selenium values constantly within the first 9 months. Therefore selenomethionine supplementation cannot be recommended.