Which metabolic disorder is characterized by an inability to break down phenylalanine, leading to intellectual disability if left untreated?

A Maple syrup urine disease
B Phenylketonuria (PKU) ✓
C Glycogen storage disease type I
D Homocystinuria

Explanation

Phenylketonuria (PKU) is a genetic disorder characterized by the inability to break down phenylalanine, an amino acid found in many protein-containing foods and some artificial sweeteners.

Mnemonic

'P'henylalanine 'K'eeps 'U'nbroken = PKU

Source

National Institutes of Health (NIH) - Genetic and Rare Diseases Information Center
Metabolic and Nutritional Disorders Genetic Metabolic Disorders Amino Acid Metabolism Disorders Hard MEDICAL Confidence: high