pediatrics
Phenylketonuria (PKU)
Key Points
PKU is caused by one of several gene mutations that result in deficiency or absence of phenylalanine hydroxylase so that dietary phenylalanine accumulates; the brain is the main organ affected, possibly because of disturbance of myelination. PKU causes a clinical syndrome of intellectual disability with cognitive and behavioral abnormalities; if untreated, the intellectual disability is severe. In the US and many developed countries, all neonates are screened for phenylketonuria 24 to 48 hours after birth with one of several blood tests; abnormal results are confirmed by directly measuring phenylalanine levels. Treatment is lifelong dietary phenylalanine restriction; adequate treatment begun in the first days of life prevents many manifestations of the disease. Although prognosis is excellent with treatment, frequent monitoring of plasma phenylalanine levels is required; recommended targets are between 2 mg/dL and 6 mg/dL (120 to 360 micromol/L) for all children. 