A 20-year-old man with a diet consisting largely of polished rice and milk presents with sore tongue, angular stomatitis, and photophobia. Slit lamp examination reveals vascularization of the cornea. The deficiency most consistent with these findings involves loss of activity of which group of enzymes?

• A Enzymes requiring NAD as coenzyme
• B Enzymes requiring pyridoxal phosphate
• C Enzymes requiring FAD and FMN as prosthetic groups ✓
• D Enzymes requiring thiamine pyrophosphate

Explanation

Corneal vascularization is the distinguishing sign of riboflavin (vitamin C2) deficiency, along with glossitis, angular stomatitis, cheilosis, and seborrheic dermatitis. Riboflavin is converted to FMN and FAD, the prosthetic groups of flavoprotein dehydrogenases and oxidases such as succinate dehydrogenase and xanthine oxidase. NAD-dependent enzymes point to niacin deficiency, which produces pellagra with dermatitis, diarrhea, and dementia, and pyridoxal phosphate deficiency produces neuropathy rather than corneal vascularization.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.