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Biochemical hallmarks of tyrosine hydroxylase deficiency
C Bräutigam1, R A Wevers, R J Jansen
1Department of Neuropaediatrics and Metabolic Diseases, University Hospital, Marburg, Germany.
Insights
Tyrosine hydroxylase (TH) deficiency is a treatable neurometabolic disorder. Diagnosis requires specific cerebrospinal fluid metabolite analysis, as urinary tests can be misleading.
Area of Science:
- Biochemistry
- Genetics
- Neurology
Background:
- Tyrosine hydroxylase (TH) deficiency is an inborn error impacting neurotransmitter synthesis.
- Clinical presentation includes hypokinesia, rigidity, and hypotonia in early infancy.
Purpose of the Study:
- To describe biochemical hallmarks and diagnostic strategies for TH deficiency.
- To report on four new cases and their treatment outcomes.
Main Methods:
- Genetic analysis identified mutations in the TH gene (exon 6 G698A and exon 3).
- Cerebrospinal fluid (CSF) metabolite analysis revealed low homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG) with normal 5-hydroxyindoleacetic acid (5-HIAA).
- Standardized lumbar puncture protocols and age-related reference values were emphasized for accurate diagnosis.
Main Results:
- Four patients presented with characteristic clinical symptoms and CSF metabolite profiles.
- Low CSF HVA and MHPG, alongside normal 5-HIAA, are reliable diagnostic indicators.
- Urinary catecholamine metabolite measurements were found to be unreliable for diagnosis.
- All patients demonstrated significant clinical improvement with L-dihydroxyphenylalanine (L-DOPA) treatment.
- CSF HVA and MHPG levels increased substantially during L-DOPA therapy.
Conclusions:
- TH deficiency is a treatable neurometabolic disorder with distinct biochemical markers.
- Accurate diagnosis relies on CSF analysis, not urinary tests.
- L-DOPA therapy is effective in improving clinical symptoms and biochemical profiles.
Abstract:
We report the biochemical hallmarks of tyrosine hydroxylase deficiency with emphasis on reliable diagnostic strategies of four new cases of an inborn error of tyrosine hydroxylase (TH). Three of our patients from different parts of the Netherlands were found homozygous for a mutation in exon 6 (G698A) of the TH gene, and one patient was found compound heterozygous for the same mutation and an additional mutation in exon 3. The first clinical symptoms of hypokinesia, rigidity of arms and legs and axial hypotonia, developed between 3 and 7 months of age. Cerebrospinal fluid investigations revealed a characteristic metabolite constellation in every case: low homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylethyleneglycol concentrations in the presence of normal reference range 5-hydroxyindolacetic acid concentrations. Strict adherence to a standardized lumbar puncture protocol and adequate age-related reference values are essential for diagnosis of this "new" treatable neurometabolic disorder. Urinary measurements of HVA, vanillylmandelic acid, and catecholamines can lead to false-negative conclusions. All patients showed a remarkable clinical improvement on a low dose of L-dihydroxyphenylalanine/ (S)-2-(3,4-dihydroxybenzyl)-2-hydrazinpropionic acid. During treatment, cerebrospinal fluid HVA, and 3-methoxy-4-hydroxy-phenylethyleneglycol increased substantially.