Inter-individuality in the transport and effect of phenylalanine in the brain: A double case report of two ‘unusual’ phenylketonuria patients

Both #A and #B have a far better outcome than expected based on their late diagnosis and dietary adherence afterwards. Although both patients had no severe neurocognitive dysfunction, slight deficits on EF and emotion regulation compared to ET-PKU cannot be ruled out. This underlines the importance of individually-tailored treatment in these patients. Interestingly, inter-individuality in the brain-to-blood phenylalanine ratio could explain the 'unusually' good outcome of patient #B, but not in patient #A. Suggesting that altered phenylalanine transport between blood and brain can explain some, but not all 'unusual' cases. Other explanations are needed and may relate to inter-individual vulnerability of the brain to elevated phenylalanine.