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On indications for treatment of the hyperphenylalaninemic neonate
Insights
Newborn screening identified infants with high phenylalanine levels. Dietary management is initiated for elevated levels, but phenylalanine tolerance tests distinguish phenylketonuria (PKU) from persistent hyperphenylalaninemia (HPA).
Area of Science:
- Biochemistry
- Neonatal screening
- Metabolic disorders
Background:
- Newborn screening programs aim to detect metabolic disorders early.
- Phenylketonuria (PKU) and persistent hyperphenylalaninemia (HPA) are conditions characterized by elevated phenylalanine levels.
Purpose of the Study:
- To evaluate the effectiveness of initial screening tests in differentiating PKU from HPA.
- To identify reliable methods for distinguishing between PKU and HPA in neonates.
Main Methods:
- Analysis of Guthrie screening test values in a large cohort of neonates.
- Confirmatory testing for infants with elevated phenylalanine levels.
- Assessment of dietary phenylalanine tolerance and 24-hour phenylalanine load tests.
Main Results:
- Out of 488,006 neonates, 58 had phenylalanine values above 2.5 mg/100 ml.
- Eighteen infants were diagnosed with PKU and fourteen with HPA.
- Initial and confirmatory tests could not differentiate between PKU and HPA.
Conclusions:
- A phenylalanine-restricted diet is initiated for infants with serum phenylalanine > 10 mg/100 ml.
- Dietary tolerance and phenylalanine load tests are crucial for differentiating PKU from HPA.
Abstract:
Of 488 006 neonates tested by Guthrie screening 58 showed values above 2.5 mg/100 ml. Thirty-two showed values between 2.5 mg/100 ml and 15 mg/100 ml. Eighteen of these infants appeared to have phenylketonuria (PKU) and fourteen to have persistent hyperphenylalaninemia (HPA). Neither the initial Guthrie test-value nor the confirmatory test were able to differentiate between these two conditions. Consequently a phenylalanine restricted diet is started in any child with serumphenylalanine values exceeding 10 mh/100 ml (605 micronmol/l). The data show that the course of the dietary tolerance of phenylalanine and a 24-hour phenylalanine load test will differentiate infants with PKU from those with HPA.