A 12-year-old boy has an intermittent scaly, hyperpigmented rash on sun-exposed skin, episodic cerebellar ataxia, and diarrhea. Urine amino acid chromatography shows generalized neutral aminoaciduria including tryptophan, while plasma amino acids are normal. The most appropriate long-term supplement is:
- A Pyridoxine
- B Nicotinamide ✓
- C Biotin
- D Hydroxocobalamin
Correct answer: B. Nicotinamide
Explanation
Hartnup disease is a defect of the intestinal and renal neutral amino acid transporter (SLC6B19/A0AT1), causing neutral aminoaciduria with normal plasma levels. Loss of urinary tryptophan reduces endogenous niacin synthesis, producing a pellagra-like dermatitis, ataxia and diarrhea, worsened by poor diet or sun exposure. Treatment is oral nicotinamide plus a high-protein diet. Pyridoxine treats CBS-responsive homocystinuria, biotin treats carboxylase deficiencies, and cobalamin treats methylmalonic acidemia.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.