NEET PG Medical – 2018 – Question – 24
Fish odor syndrome is caused by deficiency of which enzyme?
a) Fumarylacetoacetate hydrolase
b) Methane monooxygenase
c) Monooxygenase 3 (FMO3)
d) D-amino acid oxidase
Correct Answer – C
Answer: C. Monooxygenase 3 (FMO3)
Trimethylaminuria, or fish odor syndrome (FOS), is a condition characterized by the presence of trimethylamine (TMA)—a tertiary amine whose odor is described as resembling that of rotting fish—in the urine, sweat, and expired air. The cause of the syndrome is rooted in the dysfunctional metabolism of TMA, which is normally oxidized by flavin monooxygenase 3 (FMO3) into non-odorous trimethylamine-N-oxide (TMAO).
Most patients with FOS are eventually diagnosed with primary trimethylaminuria, which is caused by a deficiency in FMO3 that is inherited in an autosomal recessive fashion.
The diagnosis is made on the basis of the clinical presentation and urinalysis. Urine can be analyzed for the concentration of both TMA and TMAO, and the results may be given as an oxidizing ratio based on the formula- TMAO/(TMAO+TMA) x 100%.
Short courses of oral neomycin, metronidazole, and amoxicillin have been reported to be useful in some cases.
