Final answer:
In children with PKU, high maternal phenylalanine levels due to the mother's PKU can impair brain development and central nervous system function.
Step-by-step explanation:
The inherited disorder PKU, which causes elevated levels of phenylalanine in maternal blood, impairs brain development and central nervous system function in the unborn child. Phenylketonuria (PKU) results from a mutation in the enzyme phenylalanine hydroxylase, leading to an inability to convert phenylalanine into tyrosine, which accumulates to toxic levels. High levels of phenylalanine in pregnant women with PKU can cross the placenta, potentially resulting in physical and intellectual disabilities, microcephaly, and heart defects in the developing fetus. Therefore, it is crucial for patients with PKU to maintain a strict diet low in phenylalanine to prevent these adverse outcomes.