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Untreated PKU Patients without Intellectual Disability: What Do They Teach Us?
Danique van Vliet1, Annemiek M J van Wegberg1,2, Kirsten Ahring3
1University of Groningen, University Medical Center Groningen, Beatrix Children's Hospital, 9700 RB Groningen, The Netherlands.
Insights
Phenylketonuria (PKU) management aims to prevent brain dysfunction. However, individual responses to high phenylalanine levels vary, suggesting complex PKU pathophysiology beyond intellectual deficits.
Area of Science:
- Biochemistry
- Neuroscience
- Genetics
Background:
- Phenylketonuria (PKU) management focuses on controlling plasma phenylalanine levels to prevent neurocognitive and psychosocial dysfunction.
- Individual responses to phenylalanine concentrations vary, questioning universal treatment targets.
- Understanding inter-individual differences in brain vulnerability is crucial for optimizing PKU patient outcomes.
Purpose of the Study:
- To identify and characterize untreated/late-diagnosed PKU patients with near-normal outcomes despite high phenylalanine levels.
- To investigate the neurological, psychological, and behavioral profiles of these "unusual" PKU cases.
- To explore potential differences in PKU pathophysiology and brain vulnerability mechanisms.
Main Methods:
- Case identification of 16 untreated or late-diagnosed PKU patients with high phenylalanine levels and near-normal outcomes.
- Assessment of intellectual functioning, neurological, psychological, and behavioral status in identified cases.
- Analysis of case data to challenge classical PKU symptomatology and explore underlying mechanisms.
Main Results:
- Identified 16 PKU cases with high phenylalanine levels but relatively unaffected intellectual functioning.
- Observed neurological, psychological, and behavioral problems in these patients, indicating broader PKU effects.
- Demonstrated that lack of intellectual dysfunction does not equate to absence of phenylalanine toxicity.
Conclusions:
- Classical PKU symptomatology may need revision based on these atypical cases.
- High phenylalanine levels can be toxic to the brain even without overt intellectual impairment.
- PKU pathophysiology likely involves multiple, variable mechanisms influencing brain effects differently across individuals and ages.
Abstract:
Phenylketonuria (PKU) management is aimed at preventing neurocognitive and psychosocial dysfunction by keeping plasma phenylalanine concentrations within the recommended target range. It can be questioned, however, whether universal plasma phenylalanine target levels would result in optimal neurocognitive outcomes for all patients, as similar plasma phenylalanine concentrations do not seem to have the same consequences to the brain for each PKU individual. To better understand the inter-individual differences in brain vulnerability to high plasma phenylalanine concentrations, we aimed to identify untreated and/or late-diagnosed PKU patients with near-normal outcome, despite high plasma phenylalanine concentrations, who are still alive. In total, we identified 16 such cases. While intellectual functioning in these patients was relatively unaffected, they often did present other neurological, psychological, and behavioral problems. Thereby, these "unusual" PKU patients show that the classical symptomatology of untreated or late-treated PKU may have to be rewritten. Moreover, these cases show that a lack of intellectual dysfunction despite high plasma phenylalanine concentrations does not necessarily imply that these high phenylalanine concentrations have not been toxic to the brain. Also, these cases may suggest that different mechanisms are involved in PKU pathophysiology, of which the relative importance seems to differ between patients and possibly also with increasing age. Further research should aim to better distinguish PKU patients with respect to their cerebral effects to high plasma phenylalanine concentrations.
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