Trimethylaminuria
rare metabolic disorder
Trimethylaminuria (TMAU), also known as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder that causes a defect in the normal production of an enzyme named flavin-containing monooxygenase 3 (FMO3). When FMO3 is not working correctly or if not enough enzyme is produced, the body loses the ability to properly convert the rotting fish-smelling chemical trimethylamine (TMA) from precursor compounds in food digestion into trimethylamine oxide (TMAO), through a process called N-oxidation.
Trimethylamine can temporarily build up in the bloodstream and is released in the person's urine, sweat, and breath, giving off a rotten fish odor. Primary trimethylaminuria is caused by genetic mutations that affect the FMO3 function of the liver. Symptoms matching TMAU can also occur when there is no genetic cause, yet excessive TMA is excreted - this has been described as secondary trimethylaminuria (TMAU2).
Symptoms and signs
Trimethylamine is most noticeable in urine, as it is captured, concentrated, and released in intervals. Fishy-smelling urine is a primary identifying symptom in infant children (trimethylaminuria literally meaning "trimethylamine in urine").
Trimethylamine is also released in a person's sweat, sexual fluids, and breath, and can give off a rotten fish odor when the concentration of trimethylamine is high enough to be detected. The intensity of the smell is directly correlated with the concentration of trimethylamine in the bloodstream.
People with TMAU may have an intermittent rotten fish-like body odor, depending on diet and the severity of their FM03 mutation.
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