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KMID : 0918520150150030110
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Journal of the Korean Society of Inherited Metabolic Disease
2015 Volume.15 No. 3 p.110 ~ p.117
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Differential Diagnosis of Hyperphenylalaninemias
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Lee Jeong-Ho
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Abstract
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All infants should be screened for phenylketonuria (PKU) within the three days of life, in order to allow timely dietary intervention to protect children with PKU from neurologic damage in Korea. A commonly used cut-off level for diagnosis of PKU is 240 μmol/L (4 mg/dL). Up to 2% of cases of hyperphenylalaninemias (HPA) detected by the screening test will account for a disorder of BH4 metabolism. Therefore, analysis of blood or urinary pterins is essential, backed up with measurement of DHPR activity, as this allows differentiation of BH4 disorders. A BH4 loading test and measurement of neurotransmitters in CSF provide further important information to the severity of BH4 deficiency and BH4 loading test can detect patients with BH4 deficiency and BH4 responsive PKU. Several protocols for BH4 loading test have been described, involving treatment with BH4 for periods ranging from 1 day to 1 month, and using doses of BH4 of 10-20 mg/kg. There is general agreement that a reduction on blood phenylalanine of at least 30% in response to BH4 loading indicates a clinically significant effect, although in some tests a lower cut-off value may be defined for individual patients, or no specific cut-off value is proposed. The frequency of BH4 responsiveness is highest in patients with mild HPA and mild to moderate PKU resulting from PAH mutations with residual activity.
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KEYWORD
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Phenylketonuria, Hyperphenylalaninemia, Molecular diagnosis
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