A 4-year-old child develops painful recurrent corneal erosions and thickened palmar keratoderma. Plasma tyrosine is markedly elevated (900 micromol/L). Succinylacetone is absent from urine. Which enzyme is deficient?

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

Explanation

Tyrosinemia type II (Richner-Hanhart syndrome) results from hepatic tyrosine aminotransferase deficiency, causing tyrosine accumulation that crystallizes in corneal epithelium and skin, producing painful keratitis and palmoplantar keratosis, often with mild intellectual impairment. Absence of succinylacetone excludes type I tyrosinemia, whose enzyme fumarylacetoacetate hydrolase deficiency also causes liver failure. Homogentisate oxidase deficiency causes alkaptonuria, and p-hydroxyphenylpyruvate dioxygenase deficiency causes tyrosinemia type III.

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.