A 9-year-old boy has episodic cerebellar ataxia, pellagra-like dermatitis on sun-exposed skin, and mild intellectual disability. Urine amino acid chromatography shows generalized neutral aminoaciduria including tryptophan, while plasma levels are normal. The underlying defect is:
- A Intestinal and renal epithelial transport of neutral amino acids ✓
- B Tryptophan dioxygenase deficiency
- C Renal dibasic amino acid transport defect
- D Kynureninase deficiency
Correct answer: A. Intestinal and renal epithelial transport of neutral amino acids
Explanation
Hartnup disease results from defective apical membrane transport of neutral amino acids (SLC6A19) in intestine and proximal tubule. Plasma tryptophan falls despite urinary loss, reducing niacin synthesis and producing pellagra-like rash, ataxia, and neuropsychiatric symptoms. Treatment is oral nicotinamide plus a high-protein diet. A renal dibasic transport defect describes cystinuria, which presents with stones rather than dermatitis or ataxia.
Reference: Nelson Textbook of Pediatrics, 21st ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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