The clinical syndrome of pellagra (niacin deficiency) can occur even with adequate dietary niacin in a patient with which metabolic disorder?
- A Alkaptonuria (homogentisate accumulation)
- B Hartnup disease (defective neutral amino acid transporter SLC6A19 causing tryptophan malabsorption) ✓
- C Isovaleric acidemia
- D Propionic acidemia
Correct answer: B. Hartnup disease (defective neutral amino acid transporter SLC6A19 causing tryptophan malabsorption)
Explanation
Niacin (B3) can be synthesised endogenously from tryptophan (60 mg tryptophan yields ~1 mg niacin) via the kynurenine pathway. In Hartnup disease, the neutral amino acid transporter (SLC6A19) in intestinal and renal tubular epithelium is defective, causing profound tryptophan malabsorption despite adequate dietary intake. With depleted tryptophan, endogenous niacin synthesis is impaired, causing pellagra (dermatitis, diarrhoea, dementia) even when dietary niacin seems adequate. The disorder is otherwise managed with high-dose nicotinamide supplementation.
Reference: Harper's Illustrated Biochemistry, 32nd ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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