Amino acid metabolism: practice question

The best answer is D, Phenylalanine hydroxylase. Classic phenylketonuria is due to phenylalanine hydroxylase deficiency.

Fumarylacetoacetate hydrolase deficiency causes tyrosinaemia type I with liver failure.

Homogentisate oxidase deficiency causes alkaptonuria (dark urine, ochronosis).

Tyrosinase deficiency causes oculocutaneous albinism without the mousy odour or delay.

It tests Amino acid metabolism in Biochemistry. Phenylalanine accumulates and phenylketones give a mousy odour. Low tyrosine reduces melanin, hence the fair skin. Early dietary restriction prevents the intellectual disability.

We tag it as an application question: it asks you to use a fact on a patient or a finding. The tag is our own editorial judgement, not an official difficulty rating, so read the reason for every option, not only the answer.

Build one table of enzyme deficiency, disease, inheritance and key finding, then revise it by spaced recall. Then use the flashcards and the other Biochemistry questions on this site to test what stuck.

No. It is an original practice item (editorial status: sample, version 1). NextPrep does not publish recalled or leaked questions, and independent faculty review of this item has not been completed yet, so confirm important facts in a standard textbook.