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Genetic and Rare Diseases Information Center (GARD)

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Other Names for this Disease
  • Fish malodor syndrome
  • Fish odor syndrome
  • Stale fish syndrome
  • TMAU
  • TMAuria
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What causes trimethylaminuria?

People with trimethylaminuria lack the enzyme called flavin-containing monooxygenase 3 (FMO3), which is produced in the liver.[1] FMO3 is responsible for breaking down compounds that contain nitrogen, sulfur, or phosphorous.[1] This enzyme is produced by the FMO3 gene. A mutation in this gene prevents the enzyme from working properly, so it is unable to break down compounds like trimethylamine.  Because trimethylamine has a fish-like odor, as it builds up in a person’s body the odor becomes noticeable. Not all of the functions of the FMO3 enzyme are known, so physicians don't know what other symptoms may be associated with trimethylaminuria.[2][3]


There are several mutations, or alterations in the gene, that are associated with trimethylaminuria.  Researchers believe that a variety of genetic mutations (not yet discovered) can lead to the variability of the time of onset of symptoms and the strength of the odor. They also suspect that stress and diet play a role in triggering symptoms.[2][3][1]

Last updated: 1/27/2014

  1. Phillips IR, Shephard EA. Trimethylaminuria. GeneReviews. April 19, 2011; Accessed 1/27/2014.
  2. Learning about Trimethylaminuria. National Human Genome Research Institute Web site. July 20, 2011; Accessed 1/27/2014.
  3. Trimethylaminuria. Genetics Home Reference Web site. January 2013; Accessed 1/27/2014.