Question

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

Answer 1

The Correct Option is C

Fish odor syndrome, also known as Trimethylaminuria, is a metabolic disorder caused by a deficiency of the enzyme Monooxygenase 3 (FMO3). This enzyme is responsible for the oxidation of trimethylamine (TMA), a compound with a strong fishy odor, into trimethylamine N-oxide (TMAO), which is odorless. When FMO3 is deficient, TMA accumulates in the body and is excreted in sweat, urine, and breath, leading to the characteristic odor associated with the syndrome.

Enzyme	Function
Fumarylacetoacetate hydrolase	Involved in tyrosine metabolism
Methane monooxygenase	Oxidizes methane to methanol
Monooxygenase 3 (FMO3)	Oxidizes trimethylamine to trimethylamine N-oxide
D-amino acid oxidase	Degrades D-amino acids

In summary, the deficiency of Monooxygenase 3 (FMO3) leads to the symptoms of Fish odor syndrome due to its role in processing trimethylamine.