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Alternative names
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- Phenylalanine hydroxylase (PAH) deficiency
- Hyperphenylalaninaemia
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About the condition
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PKU is an amino acid disorder. It is a hereditary disease that is caused by a missing enzyme needed to metabolise phenylalanine. Phenylalanine is an amino acid that is present in all foods containing protein. Without treatment, phenylalanine accumulates in the blood and causes brain damage and intellectual disability.
There are milder forms of PKU (called hyperphenylalaninaemia) in which the blood phenylalanine levels are lower. Very rarely, a severe form of PKU occurs and is caused by a lack of biopterin, which is a cofactor required by the PAH enzyme.
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Inheritance
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Autosomal recessive
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Year screening started in WA
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1969 |
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Incidence in WA
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1 in 16,000 births
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Enzyme defect
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- Phenylalanine hydroxylase (PAH)
- Biopterin disorders (eg. GTPCH, DHPR deficiencies)
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Symptoms if untreated
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Infants with PKU appear normal for the first few months. However, they then begin to lose interest in their surroundings and their development slows.
Other symptoms of the condition include:
- Microcephaly
- Intellectual disability
- Seizures
- Autistic-like behaviour
- Fair-light complexion, hair and eye colour
- Musty odour
These problems can be avoided if treatment is started early.
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Metabolites on bloodspot screening
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- Increased phenylalanine
- Increased phenylalanine/tyrosine ratio
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Diagnostic tests
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- Plasma amino acids
- Urine pterins
- Bloodspot DHPR enzyme
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Treatment
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- Phenylalanine-restricted diet
- Tyrosine supplementation
- Tetrahydrobiopterin cofactor in some
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Screening issues
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The screening test is almost uniformly abnormal within 48 hours of birth, whether or not the baby is receiving full milk feeds.
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