A 12-year-old presents with photodermatitis, ataxia, and pellagra-like skin rash on sun-exposed areas. Urine indican is increased. Plasma neutral amino acids show elevated tryptophan and other neutral amino acids. Which transporter is defective?
- A Cystine transporter (SLC7A9/SLC3A1)
- B LAT1 (SLC7A5) at the blood-brain barrier
- C B0AT1 (SLC6A19) in renal and intestinal epithelia ✓
- D Neutral amino acid transporter ASC (SLC1A4)
Correct answer: C. B0AT1 (SLC6A19) in renal and intestinal epithelia
Explanation
Hartnup disease results from B0AT1 (SLC6C19) deficiency, impairing neutral amino acid absorption in kidney and intestine. Tryptophan malabsorption causes pellagra-like rash (niacin deficiency because tryptophan is a niacin precursor) and neurologic symptoms. Cystine transporter defect causes cystinuria. LAT1 defect causes amino acid transport at the blood-brain barrier.
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.