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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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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 pattern, which means that which means that both copies of the gene in each cell have mutations in order for a person to have symptoms. The parents of an individual with an autosomal recessive condition each carry one copy of the mutated gene and are referred to as "carriers" of the condition. .[1]

Since trimethylaminuria usually requires two mutations to cause symptoms, typically neither parent of an individual with trimethylaminuria has any symptoms.   Occasionally, however, carriers of one copy of an FMO3 mutation may experience mild symptoms of trimethylaminuria or have temporary episodes of fish-like odor.[1]

When two people who are carriers of an autosomal recessive condition have a child, there is a 25% (1 in 4) chance that the child will have the condition, a 50% (1 in 2) chance that the child will be a carrier like each of the parents, and a 25% (1 in 4) chance that the child will not have the condition and not be a carrier.
Last updated: 1/27/2014

What is the risk to be a carrier of a trimethylaminuria mutation?

The risk for a specific individual to be a carrier of trimethylaminuria depends on several factors, including family history and ethic background. Genetic carrier testing is available for trimethylaminuria and may help provide answers for individuals needing this information. The available data on the incidence of carriers is limited to the specific populations studied. For example, studies have reported that the incidence of heterozygous carriers in the white British population is 5/1000 to 10/1000. It has been found to be higher in other ethnic groups studied, such as 17/1000 in Jordanian, 38/1000 in Ecuadorian, and 110/1000 in New Guinean populations.[2][3]  Individuals interested in learning more about the specific risk to be a carrier for themselves or family members should speak with a genetics professional.
Last updated: 10/16/2012

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

There is typically only a risk to have a child affected with trimethylaminuria if both parents are carriers.  If a couple wants to know the chance that they are both carriers they should speak with a genetics professional.
Last updated: 10/16/2012

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: 10/18/2013