Phenylketonuria (PKU) is a rare inherited metabolic disorder in which the body cannot properly break down the amino acid phenylalanine. With early and continuous treatment, individuals with PKU can have normal development and live healthy lives.

• Cause: Caused by mutations in the PAH gene, leading to deficiency of the enzyme phenylalanine hydroxylase. This results in the buildup of phenylalanine in the blood and brain. It is inherited in an autosomal recessive pattern.

• Features: Without treatment, high phenylalanine levels can cause intellectual disability, seizures, behavioral problems, eczema, and a musty body odor. Symptoms are prevented with early diagnosis and dietary management.

• Diagnosis: Detected through newborn screening using a blood test (Guthrie test or tandem mass spectrometry).

• Treatment: Strict low-phenylalanine diet for life (avoiding high-protein foods), medical formula, and in some cases, medications like sapropterin or pegvaliase to help lower phenylalanine levels.