Fig. 2
From: Can untreated PKU patients escape from intellectual disability? A systematic review
Schematic picture outlining the hypotheses regarding the possible mechanism (s) underlying the inter-individual differences in brain vulnerability to high plasma Phe concentrations between PKU patients including: 1) a difference in the transport of Phe and other large neutral amino acids across the blood-brain barrier, 2) a difference in the transport of Phe and other large neutral amino acids across membranes of different cell types within the brain, and 3) a difference in the vulnerability of one or more of the intracerebral processes to high brain Phe concentrations