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Diseases

Genetic and Rare Diseases Information Center (GARD)

Trimethylaminuria


Other Names for this Disease
  • Fish malodor syndrome
  • Fish odor syndrome
  • Stale fish syndrome
  • TMAU
  • TMAuria
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.

Your Question

After questioning our doctor as to why our son occasionally had a fishy smell, our son was diagnosed as a carrier of trimethylaminuria.  Through genetic testing, it was identified that he has a heterozygous mutation. This obviously means that at least either myself or my husband is a carrier also.  What are the carrier incidence rates?  I am currently pregnant and am wondering what the chances are that future children could have the full syndrome.  In other words, what are the chances that the both my husband and I are carriers?

Our Answer

We have identified the following information that we hope you find helpful. If you still have questions, please contact us.

How is trimethylaminuria inherited?

Trimethylaminuria is usually inherited in an autosomal recessive manner.[1] This means that to be affected, a person must have a mutation in both copies of the responsible gene in each cell. The parents of an affected person usually each carry one mutated copy of the gene and are referred to as carriers. Carriers typically do not show signs or symptoms of the condition, although carriers of trimethylaminuria may experience mild symptoms or have temporary episodes of fish-like odor.[2] When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% chance to not have the condition and not be a carrier.
Last updated: 3/27/2015

What is the risk of being a trimethylaminuria carrier?

The risk of being a trimethylaminuria carrier depends on several factors, including family history and ethic background. Because trimethylaminuria is a rare condition, the available information on carrier risk is limited to specific populations. For example, studies have shown that 5-10 out of every 1,000 people in the white British population carry trimethylaminuria. Other reported carrier frequencies include:[3]
  • 17 out of every 1,000 people carry trimethylaminuria in Jordan
  • 38 out of every 1,000 people carry trimethylaminuria in Ecuador
  • 11 out of every 100 people carry trimethylaminuria in New Guinea

People who are interested in learning more about their specific risk of carrying trimethylaminuria should speak with a genetics professional.
Last updated: 3/26/2015

If one of my children is a carrier of trimethylaminuria, what are the chances of having an affected child?

If a child is a carrier of trimethylaminuria and has two parents without any signs or symptoms of the condition, this means that at least one of the parents is also a carrier of the condition. A carrier of trimethylaminuria has a single change (mutation) in the FMO3 gene and has a 50% chance of passing the mutation on with each pregnancy.

A couple is only at risk of having a child with trimethylaminuria if they are both carriers of the condition. The risk of being a carrier of trimethylaminuria depends on many factors, including family history and ethnic background. People who are interested in learning more about their specific risk of carrying trimethylaminuria should speak with a genetics professional.
Last updated: 3/26/2015

How can I find a genetics professional in my area?

Genetics clinics are a source of information for individuals and families regarding genetic conditions, treatment, inheritance, and genetic risks to other family members. More information about genetic consultations is available from Genetics Home Reference. To find a genetics clinic, we recommend that you contact your primary healthcare provider for a referral.

The following online resources can help you find a genetics professional in your community:
Last updated: 6/5/2014

References
Other Names for this Disease
  • Fish malodor syndrome
  • Fish odor syndrome
  • Stale fish syndrome
  • TMAU
  • TMAuria
See Disclaimer regarding information on this site. Some links on this page may take you to organizations outside of the National Institutes of Health.