A 3-year-old boy presents with painful, thickened skin lesions on the palms and soles for 6 months. Slit-lamp examination reveals bilateral crystalline corneal deposits with pseudodendritic lesions initially suspected to be herpes keratitis. Plasma tyrosine is markedly elevated. Which enzyme is deficient, and what is the appropriate dietary management?
- A Homogentisate 1,2-dioxygenase deficiency; restrict phenylalanine and tyrosine
- B Fumarylacetoacetate hydrolase (FAH) deficiency; nitisinone and restrict phenylalanine
- C Tyrosine aminotransferase (TAT) deficiency; restrict phenylalanine and tyrosine ✓
- D 4-hydroxyphenylpyruvate dioxygenase (HPD) deficiency; restrict tyrosine only
Explanation
The child has tyrosinemia type II (Richner-Hanhart syndrome) due to tyrosine aminotransferase (TAT) deficiency. It classically presents with painful palmoplantar keratoses, pseudodendritic corneal lesions, and sometimes intellectual disability. Plasma tyrosine is markedly elevated. Management is dietary restriction of both phenylalanine and tyrosine. Option B describes tyrosinemia type I, treated with nitisinone. Option A describes alkaptonuria. Option D describes tyrosinemia type III, the rarest form. The pseudodendritic corneal lesions mimicking herpes are a high-yield distinguishing feature of type II.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.