A 2-year-old boy has a diet consisting mainly of polished rice and is brought with dermatitis symmetrically distributed on sun-exposed areas, diarrhea, and dementia. Urine shows elevated 5-hydroxy indole acetic acid. What vitamin deficiency is RESPONSIBLE, and what is the BIOCHEMICAL basis?
- A Riboflavin deficiency — impaired FAD synthesis
- B Thiamine deficiency — impaired pyruvate dehydrogenase
- C Niacin deficiency — failure to convert tryptophan to NAD due to low niacin and low tryptophan ✓
- D Pyridoxine deficiency — impaired transamination of tryptophan
Explanation
This is classic pellagra (3 Ds: dermatitis, diarrhea, dementia) from niacin (vitamin B3) deficiency in a child on a maize/polished rice diet low in tryptophan. Tryptophan is the endogenous precursor of NAD/NADH, and in niacin deficiency with low tryptophan intake, NAD synthesis fails entirely. The elevated 5-HIAA in urine reflects shunting of the small amount of tryptophan available into serotonin synthesis rather than NAD. Pyridoxine deficiency can worsen pellagra by impairing the conversion of tryptophan to NAD (the conversion requires pyridoxal phosphate), but the primary deficiency here is niacin/tryptophan.
Reference: Ghai Essential Pediatrics, 10th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
Written and medically reviewed by the StethoPrep medical team.