Sections View Full Chapter Figures Tables Videos Annotate Full Chapter Figures Tables Videos Supplementary Content +++ Key Features ++ Mental retardation, hyperactivity, seizures, light complexion, and eczema characterize untreated patients Newborn screening for elevated plasma phenylalanine identifies most infants Disorders of cofactor metabolism also produce elevated plasma phenylalanine level Early diagnosis and treatment with phenylalanine-restricted diet prevents mental retardation an autosomal recessive trait, with an incidence in whites of approximately 1:10,000 live births +++ Clinical Findings ++ There is little or no phenylalanine hydroxylase activity Patients with untreated phenylketonuria exhibit severe mental retardation, hyperactivity, seizures, a light complexion, and eczema +++ Diagnosis ++ Infants should be screened during the first few days A second test is necessary when newborn screening is done before 24 hours of age, and should be completed by the third week of life Plasma phenylalanine and phenylalanine/tyrosine ratio are elevated in a child on a normal diet Plasma phenylalanine levels are persistently elevated above 1200 μM (20 mg/dL) on a regular diet, with normal or low plasma levels of tyrosine, and normal pterins +++ Treatment ++ Dietary restriction of phenylalanine Phenylalanine levels should be maintained at less than 360 μM (6 mg/dL) Your MyAccess profile is currently affiliated with '[InstitutionA]' and is in the process of switching affiliations to '[InstitutionB]'. Please click ‘Continue’ to continue the affiliation switch, otherwise click ‘Cancel’ to cancel signing in. Get Free Access Through Your Institution Learn how to see if your library subscribes to McGraw Hill Medical products. Subscribe: Institutional or Individual Sign In Username Error: Please enter User Name Password Error: Please enter Password Forgot Username? Forgot Password? Sign in via OpenAthens Sign in via Shibboleth