A newborn screened positive for elevated phenylalanine has maternal PKU. The mother has PKU but the newborn's PAH gene is normal. What condition affects the newborn?
- A Classical PKU in the newborn due to hereditary transmission
- B Transient neonatal hyperphenylalaninemia from immature liver enzymes
- C Maternal PKU syndrome — fetal exposure to high maternal phenylalanine causes microcephaly, cardiac defects, and intellectual disability despite normal fetal PAH ✓
- D Biopterin cofactor deficiency in the neonate
Explanation
Maternal PKU syndrome affects the fetus of an untreated PKU mother. High maternal phenylalanine crosses the placenta; the fetal-to-maternal ratio of phenylalanine is 1.5:1. Even though the fetus/newborn has normal PAH (heterozygous at most), prenatal exposure to phenylalanine levels >600 μmol/L causes teratogenic effects: microcephaly, intellectual disability, intrauterine growth restriction, and congenital heart defects (particularly conotruncal). The newborn's phenylalanine is elevated at birth but normalizes once breast/formula feeding begins and the mother's phenylalanine source is removed.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.