A 9-month-old infant's cloth diapers are stained black after washing. The child is otherwise developmentally normal with no organomegaly. Examination reveals pigmentation over the cheeks. Which enzyme deficiency explains these findings?

• A Homogentisate oxidase ✓
• B Tyrosinase
• C Fumarylacetoacetate hydrolase
• D Phenylalanine hydroxylase

Explanation

Alkaptonuria from homogentisate oxidase deficiency causes accumulation of homogentisic acid, which oxidises to a black pigment, staining diapers dark in infancy and later producing ochronotic pigmentation of cartilage, sclerae, and joints in adulthood. Tyrosinase deficiency causes oculocutaneous albinism without pigmentary joint disease, fumarylacetoacetate hydrolase deficiency is hereditary tyrosinemia type 1 with liver failure, and phenylalanine hydroxylase deficiency causes phenylketonuria.

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.