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Biopterin responsive phenylalanine hydroxylase deficiency.
Reuben Matalon1, Richard Koch, Kimberlee Michals-Matalon
1Department of Pediatrics and Microbiology, University of Texas Medical Branch, Galveston, Texas 77555, USA.
Summary
A pilot study found that over half of phenylketonuria (PKU) patients responded to tetrahydrobiopterin (BH4) therapy, with mutations across all PAH enzyme domains showing potential for treatment. This suggests BH4 is effective for a wider range of PKU mutations than previously thought.
Area of Science:
- Biochemistry
- Genetics
- Metabolic Disorders
Background:
- Phenylketonuria (PKU) is an inherited metabolic disorder caused by mutations in the phenylalanine hydroxylase (PAH) gene.
- Over 400 PAH gene mutations are known, leading to a wide spectrum of PKU severity.
- The efficacy of 6-R-l-erythro-5,6,7,8-tetrahydrobiopterin (BH4) has been explored in PKU patients.
Purpose of the Study:
- To investigate the response of patients with classical and atypical phenylketonuria (PKU) to 6-R-l-erythro-5,6,7,8-tetrahydrobiopterin (BH4) therapy.
- To determine the proportion of PKU patients and specific mutation types that respond to BH4 treatment.
Main Methods:
- PAH gene mutation analysis was conducted using denaturing gradient gel electrophoresis and gene sequencing.
- Patients with classical, atypical, or mild PKU received an oral dose of BH4 (10 mg/kg).
- Blood phenylalanine and tyrosine levels were measured using tandem mass spectrometry (MS/MS) at 0, 4, 8, and 24 hours post-administration.
Main Results:
- Thirty-six patients received BH4; 21 (58.33%) showed a decrease in blood phenylalanine levels.
- Responders included 12 classical, 7 atypical, and 2 mild PKU patients, with a mean phenylalanine decline of over 30% at 24 hours.
- Mutations in the catalytic, regulatory, oligomerization, and BH4 binding domains of the PAH enzyme responded to BH4; five responders had novel mutations.
Conclusions:
- A significant number of phenylketonuria (PKU) mutations respond to BH4 therapy, exceeding prior expectations.
- BH4 responsiveness is observed across all functional domains of the phenylalanine hydroxylase (PAH) enzyme.
- These findings suggest a broader potential application of BH4 in managing PKU patients with diverse genetic profiles.