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Final intelligence in late treated patients with phenylketonuria
F K Trefz1, S Cipcic-Schmidt, R Koch
1Klinik für Kinder und Jugendmedizin, Reutlingen, Germany. friedrich-karl.trefz@oe.uni-tuebingen.de
Insights
Late-treated phenylketonuria patients
Area of Science:
- Biochemistry
- Genetics
- Neurology
Background:
- Phenylketonuria (PKU) is a genetic disorder.
- Neonatal screening diagnoses most PKU cases.
- Some patients are diagnosed late, impacting outcomes.
Purpose of the Study:
- To identify factors influencing intellectual outcomes in late-treated PKU patients.
- To assess the impact of treatment initiation age and initial cognitive status.
Main Methods:
- Retrospective analysis of 40 late-treated PKU patients.
- Data included age at diagnosis, treatment start, IQ/DQ scores, and final IQ.
- Neuroimaging and spectroscopy in select cases.
Main Results:
- Late treatment significantly improved IQ (52.7 to 79.0).
- Earlier treatment start and higher initial IQ/DQ correlated with better final intelligence.
- Two untreated patients had normal IQs, suggesting protective factors.
Conclusions:
- Treatment initiation age and baseline intellectual status are key predictors of final IQ in late-treated PKU.
- Genetic factors may influence brain damage severity in PKU.
- Further research into protective mechanisms is warranted.
Unlabelled:
Despite neonatal screening programmes, there is still a number of patients with phenylketonuria who are not diagnosed and start treatment late. The question in this study was to evaluate which factors will contribute, other than the quality and duration of dietary treatment, to final outcome in late treated patients with phenylketonuria. We retrospectively analysed the data of 40 patients with phenylketonuria, of whom 2 patients at 35 and 24 years of age had a normal IQ despite never being treated. In 38 patients starting dietary treatment between 0.7 and 7 years of age, mean IQ/DQ at diagnosis was 52.7 (SD = 16) (mean age 2.5 years), final IQ (mean age 33.5 years) was 79.0 (SD = 16), the difference was highly significant (P < 0.0001). Important factors for the final intelligence in adult late treated patients with phenylketonuria were onset (r = -0.46, P < 0.009) and DQ/IQ (r = 0.51, P < 0.002) when dietary treatment was started. Thus, in late treated patients with phenylketonuria, in addition to the quality and duration of treatment, the outcome is mainly influenced by the age of starting treatment and also by the intellectual status of the patient. In one of the two patients with normal intelligence, nuclear magnetic resonance spectroscopy showed that brain phenylalanine was undetectable even though blood phenylalanine was 30 mg/dl. A second metabolic disorder may protect these patients from severe brain damage.
Conclusion:
These data indicate that brain damage in untreated or late treated patients with phenylketonuria is influenced by various genetic factors.