Step 1

Biochemistry 14

A 9-month-old girl presents with her parents to the pediatrician for a well child visit. The newborn screening panel for the girl indicated an absence of phenylalanine hydroxylase. The child is doing well and the parents indicate no concerns. The child is meeting all developmental milestones. Vital signs are within normal limits, and physical examination reveals no abnormalities or overt manifestations of the disease process. The mother indicates they have been compliant with the prescribed formula and inquires about starting solid foods.

Which of the following amino acids is essential in her condition and should be recommended for supplementation after weening from formula?

  • A) Cysteine
  • B) Isoleucine
  • C) Phenylalanine
  • D) Tyrosine
  • E) Valine


Jeanita Littrell


Dr. Ted O'Connell