SELENOP and phenylketonuria: Furthermore, both the PKU and the healthy control groups in the studies were found to have selenium status that was low or close to lower European population norms in some studies [44, 45, 67, 69–74] Therefore, at this time further research is warranted investigating selenium status in PKU and the effects of supplementation including measurement of plasma selenoprotein P (SEPP1) as a more informative marker of status.