UKMLA PLAB AMC USMLE Prometric MCQ

Question Number 0228
Question:
A middle-eastern male child with a fair complexion adopted soon after his premature birth is noted to have delayed milestones at 8 months of age. He is also noted to have eczema. At two years of age the child has severe mental retardation with no pyramidal or extrapyramidal signs. Mental retardation in this child is most likely secondary to a defect in

a) Creatine phosphokinase
b) troponin T
c) phenylalanine hydroxylase
d) aspartate aminotransferase
e) alanine aminotransferase