Case history
Case history
A full-term, female infant presents at 4 days of age with a positive newborn screening test for phenylketonuria (PKU). The history is unremarkable and physical examination reveals no abnormal findings. Plasma amino acid analysis shows a phenylalanine level of 1211 micromol/L (20 mg/dL) (normal levels are 61-121 micromol/L [1-2 mg/dL]), with all other amino acids within normal ranges. Urine neopterin to biopterin ratio and blood dihydropteridine reductase activity are subsequently normal, ruling out a defect in tetrahydrobiopterin (BH4) synthesis or recycling.
Other presentations
Although in developed nations almost all patients with PKU are diagnosed through newborn screening, the same is not true in developing countries. If a child from a developing nation should present with developmental delay, microcephaly, intellectual disability, or behavioural disturbances, the diagnosis of PKU should be considered. The presence of eczema may provide an additional clue. PKU should also be ruled out in any patient with intellectual disability that was born before the mid-to late 1960’s, as routine screening at birth was only introduced then.
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