Question

Fishy odour occurs due to deficiency of which vitamin from the diet?

• A. Biotin
• B. Thiamine
• C. Riboflavin
• D. Vitamin A

Hint:

Think of the flavin-containing enzyme FMO3 and the vitamin that supplies its cofactor.

Answer 1

The Correct Option is C

Step 1: The fishy body odour described here is trimethylaminuria (fish-odour syndrome), a metabolic disorder in which trimethylamine accumulates and is excreted in sweat, saliva and urine, giving a rotten-fish smell.
Step 2: Trimethylamine is normally produced by gut bacteria from dietary choline and trimethylamine oxide, then oxidised in the liver to odourless trimethylamine N-oxide by the enzyme flavin-containing monooxygenase 3 (FMO3). FMO3 is a flavin-dependent enzyme, so it needs the flavin cofactors FAD and FMN, both derived from riboflavin (vitamin B2).
Step 3: When riboflavin is deficient, residual FMO3 activity falls, trimethylamine is not converted, and the fishy odour appears. Riboflavin supplementation is given to enhance residual FMO3 activity, confirming the link. Hence the answer is Riboflavin.
Step 4: The distractors are wrong because biotin deficiency causes dermatitis and alopecia, thiamine deficiency causes beriberi and Wernicke encephalopathy, and vitamin A deficiency causes night blindness and xerophthalmia - none produce a fishy odour.