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Iatrogenic and transient hyperglycinemia in patients with phenylketonuria
Insights
Newborn screening identified phenylketonuria in two infants treated with low phenylalanine diets. While phenylalanine was controlled, elevated glycine levels normalized by five months, suggesting immature glycine metabolism in infants.
Area of Science:
- Biochemistry
- Metabolic Disorders
- Neonatal Medicine
Background:
- Phenylketonuria (PKU) is an inborn error of metabolism requiring dietary management.
- Newborn screening programs are crucial for early detection and intervention.
- Dietary management of PKU involves limiting phenylalanine intake.
Observation:
- Two infants diagnosed with PKU via newborn screening were treated with specialized low-phenylalanine formulas.
- Serum phenylalanine levels were effectively managed with the prescribed formula.
- Transiently elevated serum glycine levels were observed in both infants during the first 4-5 months of life.
Findings:
- Elevated glycine levels were likely a consequence of the high glycine content in the therapeutic formulas.
- Serum glycine levels normalized spontaneously by 4-5 months of age despite continued use of the same formula.
- This normalization suggests an immature glycine metabolism in infants that matures over the first few months of life.
Implications:
- Infants may have transiently immature glycine metabolism, impacting tolerance to high-glycine formulas.
- Monitoring glycine levels in infants on specific metabolic formulas may be warranted.
- Understanding infant metabolic development is key to optimizing nutritional therapies for inborn errors of metabolism.
Abstract:
Two patients with phenylketonuria detected by newborn screening for inborn errors of metabolism were treated with low phenylanine formulae. Serum phenylalanine levels were well controlled, but serum glycine levels were elevated until 4 or 5 months of age. This was probable due to the high content of glycine in the formulae. Glycine level returned to be normal in these patients, even though they were kept on the same formula, suggesting, immature metabolism of glycine during this period. No clinical problems were encountered in either patient.