SynopsisCodesLook ForDiagnostic PearlsDifferential Diagnosis & PitfallsBest TestsManagement PearlsTherapyReferences

View all Images (3)

Phenylketonuria in Adult
Other Resources UpToDate PubMed

Phenylketonuria in Adult

Contributors: Vivian Wong MD, PhD, Lowell A. Goldsmith MD, MPH
Other Resources UpToDate PubMed


Phenylketonuria (PKU) is an autosomal recessive disorder of phenylalanine metabolism. PKU screening is now part of standard neonatal screening in most countries for inborn errors of metabolism. Accumulation of phenylalanine and its metabolites are thought to be responsible for the pathologies seen in PKU.

The untreated state is characterized by a constellation of functional and physical manifestations including intellectual disability, a characteristic bodily appearance, and neurological impairments. Intellectual disability worsens from early childhood to adolescence during brain maturation. Patients develop the classic triad of blond hair, blue eyes, and light skin usually by the second year of life. Atopic dermatitis may occur, and sclerodermatous changes limited to skin and connective tissue have been reported. Patients may also have neuropsychiatric abnormalities.


E70.0 – Classical phenylketonuria

7573000 – Classical phenylketonuria

Look For

Subscription Required

Diagnostic Pearls

Subscription Required

Differential Diagnosis & Pitfalls

Hypopigmentation of skin:
  • Oculocutaneous albinism
  • Copper deficiency and Selenium deficiency
  • Homocystinuria
  • Histidinemia
  • Chediak-Higashi syndrome
Sclerodermatous skin changes:
  • Scleroderma of childhood – Also favors lower extremities but may involve hands and feet. Scl-70 antibody is positive.
  • Scleredema – Favors the face, neck, and upper back.
  • Stiff skin syndrome – Affects the entire body. Hypertrichosis is also present.
  • Subcutaneous fat necrosis of the newborn – Self-limited, localized sclerodermatous changes in newborns.

Best Tests

Subscription Required

Management Pearls

Subscription Required


Subscription Required


Subscription Required

Last Updated:04/24/2022
Copyright © 2024 VisualDx®. All rights reserved.
Phenylketonuria in Adult
A medical illustration showing key findings of Phenylketonuria : Dry skin, Microcephaly, Osteopenia, Developmental delay
Clinical image of Phenylketonuria - imageId=5455459. Click to open in gallery.
Copyright © 2024 VisualDx®. All rights reserved.