A toddler presents with bilateral photophobia, lacrimation, and painful palmoplantar keratoderma. Slit lamp examination shows dendritic corneal lesions that stain poorly with fluorescein. Plasma tyrosine is 900 micromol/L. The deficient enzyme is:

• A Tyrosine aminotransferase ✓
• B Fumarylacetoacetate hydrolase
• C p-Hydroxyphenylpyruvate dioxygenase
• D Homogentisate oxidase

Explanation

Tyrosinemia type II (Richner-Hanhart syndrome) results from hepatic tyrosine aminotransferase deficiency, causing tyrosine crystals to deposit in corneal epithelium as pseudodendritic ulcers and in skin as painful palmoplantar keratosis. Fumarylacetoacetate hydrolase deficiency defines type I with succinylacetone, option B. p-Hydroxyphenylpyruvate dioxygenase is blocked in tyrosinemia type III and pharmacologically by nitisinone, option C. Homogentisate oxidase deficiency causes alkaptonuria without keratopathy, eliminating option D.

Reference: Robbins and Cotran Pathologic Basis of Disease, 10th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.