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"Hypotyrosinemia" in phenylketonuria.
W B Hanley1, A W Lee, A J Hanley
1Division of Clinical & Biochemical Genetics, The Hospital for Sick Children, Toronto, Ontario, Canada. whanley@sickkids.on.ca
Molecular Genetics and Metabolism
|June 28, 2000
Summary
Phenylketonuria (PKU) patients exhibit low plasma tyrosine levels, potentially impacting neurotransmitter production and contributing to learning disabilities. This study confirms hypotyrosinemia in PKU, highlighting a critical area for further research.
Area of Science:
- Biochemistry
- Neuroscience
- Genetics
Background:
- Phenylketonuria (PKU) is associated with learning disabilities, possibly due to impaired neurotransmitter synthesis.
- Reduced tyrosine transport across the neuronal membrane is a suspected cause of hypotyrosinemia in PKU patients.
- Limited data exist on plasma tyrosine levels in individuals with PKU.
Purpose of the Study:
- To investigate plasma tyrosine levels in patients with classical PKU, mild (atypical) PKU, and non-PKU mild hyperphenylalaninemia.
- To compare these levels with data from normal individuals and published literature.
Main Methods:
- Plasma tyrosine concentrations were measured in 99 classical PKU patients, 26 mild PKU patients, and 35 non-PKU mild hyperphenylalaninemia patients.
- Data were compared with 102 non-PKU subjects from a hospital database, 58 volunteers, and literature values.
Main Results:
- Mean nonfasting plasma tyrosine was significantly lower in classical PKU patients (41.1 micromol/L) and mild PKU patients (53.3 micromol/L) compared to non-PKU controls (64.0-69.1 micromol/L).
- Patients with non-PKU mild hyperphenylalaninemia had slightly lower tyrosine levels (66.6 micromol/L) than controls.
- The findings support existing hypotheses of hypotyrosinemia in PKU.
Conclusions:
- Plasma tyrosine levels are confirmed to be low in patients with phenylketonuria.
- This finding supports the hypothesis that hypotyrosinemia may contribute to neurological complications in PKU.
- Further research is warranted to explore the link between tyrosine deficiency, neurotransmitter production, and learning disabilities in PKU.