Medicine & USMLE

Hartnup Disease

  1. Vitamin B1 (Thiamine) Biochemistry
  2. Vitamin B1 (Thiamine) Deficiency
  3. Vitamin B2 (Riboflavin)
  4. Vitamin B3 (Niacin) Biochemistry
  5. Vitamin B3 (Niacin) Deficiency and Excess
  6. Hartnup Disease
  7. Vitamin B5 (Pantothenic Acid)
  8. Vitamin B6 (Pyridoxine)
  9. Vitamin B7 (Biotin)
  10. Vitamin B9 (Folate)
  11. Vitamin B12 (Cobalamin) Biochemistry
  12. Vitamins B9 and B12 Deficiencies
  13. Vitamin A (Retinol) Biochemistry
  14. Vitamin A (Retinol) Deficiency and Excess
  15. Vitamin C (Ascorbic Acid) Biochemistry
  16. Vitamin C (Ascorbic Acid) Deficiency and Excess
  17. Vitamin D Biochemistry
  18. Vitamin D Deficiency and Excess
  19. Vitamin E (Tocopherol/Tocotrienol)
  20. Vitamin K Biochemistry
  21. Vitamin K Deficiency
  22. Zinc
  23. Kwashiorkor and Marasmus


Hartnup Disease is an autosomal recessive metabolic disorder characterized by a dysfunction in the neutral amino acid transporter. This defect causes decreased absorption of nonpolar amino acids, specifically tryptophan. Since tryptophan is important for the synthesis of Vitamin B3 (Niacin), patients with Hartnup disease will also present with signs and symptoms consistent with Niacin Deficiency), with pellagra-like symptoms. Since clinical findings are primarily due to niacin/tryptophan deficiency, niacin supplementation and/or a high-protein diet can be used to treat the disease.

Key Points

  • Hartnup Disease
    • Autosomal recessive inheritance
    • Deficiency of neutral amino acid (eg, tryptophan) transporters in proximal renal tubular cells and on enterocytes
      • Increased excretion of tryptophan in urine and decreased absorption from the gut → decreased tryptophan levelsdecreased conversion to niacin --> pellagra-like symptoms
    • Treat with high-protein diet and nicotinic acid (niacin)

Find Hartnup Disease and other Vitamins among Pixorize's visual mnemonics for the USMLE Step 1 and NBME shelf exams.