Which enzyme is deficient in the genetic disorder known as phenylketonuria?

A Phenylalanine hydroxylase ✓
B Tyrosinase
C Trypsin
D Lactate dehydrogenase

Explanation

Phenylketonuria is a genetic disorder caused by a deficiency of the enzyme phenylalanine hydroxylase, which is necessary for the breakdown of the amino acid phenylalanine.

Source

Guyton and Hall Textbook of Medical Physiology
Enzymes in Disease Genetics Inborn Errors of Metabolism Hard MEDICAL Confidence: high