Updated: 12/25/2021

Phenylketonuria

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  • Snapshot
    • A 2-month-old infant was born with blond hair, blue eyes, and fair skin. It is noticed he has an eczematous rash and is vomiting. In addition he has a musty, mousy odor.
  • Introduction
    • Screened for at birth in the US by one of the following
      • Guthrie bacterial inhibition study
      • automated fluorimetric assay
      • tandem mass spectrometry
    • Caused from a decrease in phenylalanine hydroxylase or tetrahydrobiopterin cofactor
      • normally converts phenyalanine into tyrosine
      • therefore tyrosine becomes essential
      • phenylalanine builds up leading to excess phenylketones which cause brain damage
  • Presentation
    • Infants are normal at birth
    • After a few months mental retardation is evident
    • Present with
      • blond, blue eyed, with fair skin
      • mental retardation
      • eczema
      • musty body odor of phenyacetic acid
      • vomiting is common and is often mistaken for pyloric stenosis
    • Physical exam shows
      • hyperactive deep tendon reflexes
  • Treatment
    • Decreased phenylalanine diet
      • early institution is essential to prevent the development of brain damage
    • Increase tyrosine in diet
    • Pregnant mothers with PKU must go back on a low phenylalanine diet before conception and through pregnancy to reduce the risk of birth defects

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(M2.PD.15.4676) A 29-year-old woman presents to her OB/GYN for a preconception visit. She wishes to become pregnant within the next several months. A thorough history reveals that the patient suffers from phenylketonuria (PKU). She recalls being instructed by prior physicians to follow a diet that avoids certain foods; however, she admits to not being complaint with these recommendations. Laboratory testing reveals a plasma phenylalanine level of 20.2 mg/dL (normal range <2 mg/dL). Which of the following is the most appropriate response to this patient?

QID: 107225

Even with appropriate treatment, your condition will prevent you from becoming pregnant

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(0/40)

Improved PKU treatment will decrease the risks of spontaneous abortion and intrauterine fetal death

42%

(17/40)

3 months prior to conception, begin a restricted diet to lower phenylalanine levels to below 6 mg/dL

35%

(14/40)

Begin a phenylalanine-restricted diet in your first trimester to reduce the risk of fetal morbidity

18%

(7/40)

Your current phenylalanine levels do not pose a risk to any future pregnancy

2%

(1/40)

M 8 E

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