고페닐알라닌혈증의 진단 및 평가 = Differential Diagnosis of Hyperphenylalaninemias

다국어 초록 (Multilingual Abstract)

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 $240{\mu}mol/L$ (4 mg/dL). Up to 2% of cases of hyperphenylalaninemias (HPA) detected by the screening test will account for a disorder of $BH_4$ metabolism. Therefore, analysis of blood or urinary pterins is essential, backed up with measurement of DHPR activity, as this allows differentiation of $BH_4$ disorders. A $BH_4$ loading test and measurement of neurotransmitters in CSF provide further important information to the severity of $BH_4$ deficiency and $BH_4$ loading test can detect patients with $BH_4$ deficiency and $BH_4$ responsive PKU. Several protocols for $BH_4$ loading test have been described, involving treatment with $BH_4$ for periods ranging from 1 day to 1 month, and using doses of $BH_4$ of 10-20 mg/kg. There is general agreement that a reduction on blood phenylalanine of at least 30% in response to $BH_4$ 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 $BH_4$ responsiveness is highest in patients with mild HPA and mild to moderate PKU resulting from PAH mutations with residual activity.