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Trimethylaminuria is a disorder in which the body is unable to break down trimethylamine, a chemical compound that has a pungent odor. Trimethylamine has been described as smelling like rotten or decaying fish. As this compound builds up in the body, it causes affected people to give off a strong fishy odor in their sweat, urine, and breath. The intensity of the odor may vary over time. The odor can interfere with many aspects of daily life, affecting a person's relationships, social life, and career. Some people with trimethylaminuria experience depression and social isolation as a result of this condition.


Trimethylaminuria is an uncommon genetic disorder; its incidence is unknown.


Variants (also known as mutations) in the FMO3 gene cause trimethylaminuria. This gene provides instructions for making an enzyme that breaks down nitrogen-containing compounds from the diet, including trimethylamine. This compound is produced by bacteria in the intestine during the digestion of eggs, liver, legumes (such as soybeans and peas), certain kinds of fish, and other foods. Normally, the FMO3 enzyme converts strong-smelling trimethylamine into another molecule that has no odor. If the enzyme is missing or its activity is reduced because of a variant in the FMO3 gene, trimethylamine is not processed properly and can build up in the body. As excess trimethylamine is released in a person's sweat, urine, and breath, it causes the odor characteristic of trimethylaminuria. Researchers believe that stress and diet also play a role in triggering symptoms.

Although FMO3 gene variants account for most cases of trimethylaminuria, the condition can also be caused by other factors. The strong body odor may result from an excess of certain chemical compounds in the diet or from an abnormal increase in bacteria that produce trimethylamine in the digestive system. A few cases of the disorder have been identified in adults with liver or kidney disease. Temporary symptoms of this condition have been reported in a small number of premature infants and in some healthy women at the start of menstruation.


Most cases of trimethylaminuria appear to be inherited in an autosomal recessive pattern, which means both copies of the gene in each cell have variants. Most often, the parents of an individual with an autosomal recessive condition each carry one copy of the altered gene, but typically do not show signs and symptoms of the condition. Carriers of an FMO3 variant, however, may have mild symptoms of trimethylaminuria or experience temporary episodes of strong body odor.

Other Names for This Condition

  • Fish malodor syndrome
  • Fish odor syndrome
  • Stale fish syndrome
  • TMAU
  • TMAuria

Additional Information & Resources

Genetic Testing Information

Genetic and Rare Diseases Information Center

Patient Support and Advocacy Resources

Clinical Trials

Catalog of Genes and Diseases from OMIM

Scientific Articles on PubMed


  • Chalmers RA, Bain MD, Michelakakis H, Zschocke J, Iles RA. Diagnosis and management of trimethylaminuria (FMO3 deficiency) in children. J Inherit Metab Dis. 2006 Feb;29(1):162-72. doi: 10.1007/s10545-006-0158-6. Citation on PubMed
  • Christodoulou J. Trimethylaminuria: an under-recognised and socially debilitating metabolic disorder. J Paediatr Child Health. 2012 Mar;48(3):E153-5. doi: 10.1111/j.1440-1754.2010.01978.x. Epub 2011 Jan 31. Citation on PubMed
  • Hernandez D, Addou S, Lee D, Orengo C, Shephard EA, Phillips IR. Trimethylaminuria and a human FMO3 mutation database. Hum Mutat. 2003 Sep;22(3):209-13. doi: 10.1002/humu.10252. Citation on PubMed
  • Mitchell SC, Smith RL. Trimethylaminuria: the fish malodor syndrome. Drug Metab Dispos. 2001 Apr;29(4 Pt 2):517-21. Citation on PubMed
  • Mitchell SC. Trimethylaminuria: susceptibility of heterozygotes. Lancet. 1999 Dec 18-25;354(9196):2164-5. doi: 10.1016/s0140-6736(05)77067-7. No abstract available. Citation on PubMed
  • Phillips IR, Shephard EA. Primary Trimethylaminuria. 2007 Oct 8 [updated 2020 Nov 5]. In: Adam MP, Feldman J, Mirzaa GM, Pagon RA, Wallace SE, Bean LJH, Gripp KW, Amemiya A, editors. GeneReviews(R) [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2024. Available from Citation on PubMed
  • Shephard EA, Treacy EP, Phillips IR. Clinical utility gene card for: trimethylaminuria. Eur J Hum Genet. 2012 Mar;20(3). doi: 10.1038/ejhg.2011.214. Epub 2011 Nov 30. No abstract available. Citation on PubMed or Free article on PubMed Central
  • Shimizu M, Cashman JR, Yamazaki H. Transient trimethylaminuria related to menstruation. BMC Med Genet. 2007 Jan 27;8:2. doi: 10.1186/1471-2350-8-2. Citation on PubMed or Free article on PubMed Central
  • Wise PM, Eades J, Tjoa S, Fennessey PV, Preti G. Individuals reporting idiopathic malodor production: demographics and incidence of trimethylaminuria. Am J Med. 2011 Nov;124(11):1058-63. doi: 10.1016/j.amjmed.2011.05.030. Epub 2011 Aug 16. Citation on PubMed
  • Yamazaki H, Fujieda M, Cashman JR, Kamataki T. Mild trimethylaminuria observed in a Japanese cohort with liver damage. Am J Med. 2005 Jul;118(7):803-5. doi: 10.1016/j.amjmed.2004.08.015. No abstract available. Citation on PubMed
  • Zschocke J, Kohlmueller D, Quak E, Meissner T, Hoffmann GF, Mayatepek E. Mild trimethylaminuria caused by common variants in FMO3 gene. Lancet. 1999 Sep 4;354(9181):834-5. doi: 10.1016/s0140-6736(99)80019-1. Citation on PubMed

The information on this site should not be used as a substitute for professional medical care or advice. Contact a health care provider if you have questions about your health.