A child with alkaptonuria will eventually develop ochronosis and arthritis. The enzyme deficient in this condition and the substrate that accumulates is:

• A Fumarylacetoacetase; fumarylacetoacetate
• B Homogentisate 1,2-dioxygenase; homogentisic acid ✓
• C p-Hydroxyphenylpyruvate dioxygenase; p-hydroxyphenylpyruvate
• D 4-Maleylacetoacetate isomerase; maleylacetoacetate

Explanation

Alkaptonuria is caused by deficiency of homogentisate 1,2-dioxygenase, an enzyme in the tyrosine degradation pathway. Homogentisic acid (HGA) accumulates, is excreted in urine (which darkens on standing due to oxidation), and deposits as a dark polymer (ochronosis) in connective tissues, cartilage, and joints causing degenerative arthropathy. Fumarylacetoacetase deficiency causes tyrosinemia type I with succinylacetone accumulation.

Reference: Harper's Illustrated Biochemistry, 32nd ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.