Deficiency of Phenylalanine Hydroxylase

Also written as PAH.

Deficiency of phenylalanine hydroxylase → cannot convert phenylalanine to tyrosine

What our notes say

• Deficiency of phenylalanine hydroxylase → cannot convert phenylalanine to tyrosine (Genetic Disorders Pathology Crash Course: Exam Revision Notes)

Study material on Deficiency of Phenylalanine Hydroxylase

• Chemical Pathology Practice Examination

Practice questions on Deficiency of Phenylalanine Hydroxylase

Phenylketonuria (PKU) is caused by deficiency of phenylalanine hydroxylase. Untreated it causes

• Hepatomegaly and cirrhosis
• Severe intellectual disability, seizures, musty odor, fair skin and hair, eczema
• Hemolytic anemia and jaundice
• Renal tubular acidosis and rickets

Answer: B. Phenylalanine accumulates → phenylketones in urine (musty/mousy odor). Blocks tyrosine synthesis → decreased melanin (fair skin/hair/eyes). Autosomal recessive. Diagnosed on newborn screening (Guthrie test/tandem mass spectrometry). Treatment: phenylalanine-restricted diet + sapropterin in BH4-responsive cases. Start treatment immediately to prevent intellectual disability. ---

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