Abstract
Pegvaliase, an injectable form of phenylalanine ammonia lyase, is an enzyme substitution therapy for adults with phenylketonuria (PKU). Experience with pegvaliase during lactation is scarce. Limited evidence suggests that pegvaliase does not pass into breast milk. The case presented here describes the pregnancy and lactation experience of a woman with PKU who was treated with pegvaliase prior to pregnancy, discontinued pegvaliase and was treated with a phenylalanine-restricted diet in preparation for and during pregnancy, and then reinstituted pegvaliase two weeks after giving birth and throughout lactation. No pegvaliase activity was detected in pumped breast milk samples prior to reinstituting pegvaliase, and at doses of 80, 110 and 140 mg/week during lactation. The phenylalanine content of breast milk samples collected during pegvaliase therapy were not significantly different than controls, and the infant has grown and developed normally, indicating that pegvaliase therapy during lactation is safe.