Is Trimethylaminuria hereditary?

Trimethylaminuria is a genetic metabolic condition typically inherited in an autosomal recessive pattern, meaning both parents must carry a variant in the FMO3 gene for a child to be affected. While it is hereditary, the clinical expression of trimethylaminuria can vary significantly between individuals, even within the same family, due to environmental and dietary factors.

Is trimethylaminuria considered hereditary?

Yes, trimethylaminuria is a hereditary condition caused by mutations in the FMO3 (flavin-containing monooxygenase 3) gene. Being "hereditary" means the genetic instructions for the enzyme responsible for breaking down trimethylamine are passed from parents to children. It is not contagious and cannot be acquired through environmental exposure alone, though diet plays a massive role in symptom severity.

What is the inheritance pattern of trimethylaminuria?

Trimethylaminuria follows an autosomal recessive inheritance pattern. This means that a person with the condition has inherited two copies of the non-functional gene—one from each parent. Parents of an individual with trimethylaminuria are typically "carriers," meaning they have one functional copy of the gene and one variant, and they usually do not exhibit symptoms themselves.

What are the risks for family members?

If both parents are carriers of a pathogenic FMO3 variant, the risk profile for each pregnancy is as follows:

• 25% chance the child will have trimethylaminuria.


• 50% chance the child will be an asymptomatic carrier.


• 25% chance the child will inherit two functional copies of the gene.

Is genetic testing available for this condition?

Yes, molecular genetic testing via sequencing of the FMO3 gene is available to confirm a diagnosis of trimethylaminuria. Testing is recommended for individuals presenting with persistent body odor resembling rotting fish, particularly if dietary management has been ineffective. Genetic counseling is highly recommended for families planning a pregnancy to discuss carrier testing and the potential for recurrence in future children. De novo (spontaneous) mutations are not the primary cause of trimethylaminuria; the condition is overwhelmingly familial.

Next steps

• Consult with a metabolic specialist or a clinical geneticist to discuss diagnostic sequencing.


• Connect with the 34 members of the trimethylaminuria community on DiseaseMaps.org to share experiences.


• Work with a registered dietitian to identify food triggers that exacerbate symptoms.


• Request a referral to a genetic counselor to map family history and discuss reproductive risks.

Medical disclaimer: This information is for educational purposes only and should not replace professional medical advice, diagnosis, or treatment.

References

• NIH Genetic and Rare Diseases Information Center (GARD): Trimethylaminuria


• Orphanet: Trimethylaminuria (ORPHA:93963)


• OMIM (Online Mendelian Inheritance in Man): FMO3 Gene (#603995)


• National Library of Medicine: GeneReviews for FMO3-related disorders