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Brain uptake of 11C-methionine in phenylketonuria
Insights
Phenylketonuria (PKU) affects brain uptake of methionine, an essential amino acid. High phenylalanine levels in PKU patients significantly decrease methionine brain uptake, particularly in early childhood.
Area of Science:
- Neuroscience
- Biochemistry
- Pediatrics
Background:
- Classical phenylketonuria (PKU) is a genetic disorder characterized by elevated blood phenylalanine levels.
- Amino acid transport across the blood-brain barrier is crucial for brain development and function.
- Methionine is an essential amino acid vital for protein synthesis and neurotransmitter metabolism.
Purpose of the Study:
- To investigate the impact of phenylketonuria and phenylalanine levels on brain uptake of 11C-methionine in children.
- To assess 11C-methionine brain uptake as a potential indicator of blood-brain barrier permeability and brain maturation in PKU.
- To determine the age-dependent changes in brain methionine uptake in relation to phenylalanine levels.
Main Methods:
- Utilized positron emission tomography (PET) with the radiotracer 11C-methionine to measure brain uptake in 26 children with classical PKU and one adult control.
- Measured brain methionine uptake during a low phenylalanine diet and after an acute phenylalanine load.
- Analyzed brain activity curves and blood phenylalanine and methionine levels over time, considering age and disease severity.
Main Results:
- In children with phenylalaninemia ≤ 0.3 µmol/mL, brain methionine uptake decreased with age, most notably in the first year of life.
- A tenfold increase in blood phenylalanine levels led to a twofold decrease in brain methionine uptake, while blood methionine remained stable.
- Brain activity curves for 11C-methionine increased with time in infants (<1 year) with phenylalaninemia < 0.6 µmol/mL, whereas older children (>2 years) showed decreasing curves.
Conclusions:
- 11C-methionine brain uptake serves as a valuable index for assessing blood-brain barrier permeability to essential amino acids and brain maturation in PKU.
- Elevated phenylalaninemia (≥ 0.6 µmol/mL) significantly alters amino acid brain uptake, especially during the critical first two years of life.
- These findings highlight the importance of early and effective management of hyperphenylalaninemia to support normal brain development in children with PKU.
Abstract:
The brain uptake of 11C-methionine was studied in 26 children with classical phenylketonuria; one adult was used as a control. Labelled methionine uptake in brain was first measured during a low phenylalanine diet and again one week later after a load of phenylalanine. Ten children aged 1 to 30 months were studied twice at intervals of several months. In children having a phenylalaninemia less than or equal to 0.3 mumoles . ml-1, a decrease in methionine brain uptake was observed with increasing age, with the largest change occurring during the first year of life. After the phenylalanine load, a mean increase in phenylalaninemia by a factor of ten was accompanied by a mean decrease in brain methionine uptake by a factor of two while blood methionine remained unchanged. Brain activity curves increased with time for children younger than one year and having phenylalaninemia less than 0.6 mumoles . ml-1. After the age of 2 most patients had a decreasing curve regardless of the blood phenylalanine level. This study indicates that 11C-methionine brain uptake may be taken as an index of blood barrier permeability to essential amino acids, and of brain maturation. The results obtained suggest that an increase in phenylalaninemia to levels greater than 0.6 mumole . ml-1 induces a modification in brain uptake of amino acids, primarily during the first two years of life.