Trimethylaminuria

Trimethylaminuria is a disorder in which the body is unable to break down trimethylamine, a compound derived from the diet that has a strong odor of rotting fish. As trimethylamine builds up in the body, it causes affected people to give off a fish-like odor in their sweat, urine, and breath. The intensity of this odor may vary over time. The strong body 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.

Although gene mutations account for most cases of trimethylaminuria, the condition can also be caused by other factors. A fish-like body odor may result from an excess of certain proteins in the diet or from an increase in bacteria that normally 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.

How common is trimethylaminuria?

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

What genes are related to trimethylaminuria?

Mutations in the FMO3 gene cause trimethylaminuria.

The FMO3 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 as they help digest proteins from eggs, liver, legumes (such as soybeans and peas), certain kinds of fish, and other foods. Normally, the FMO3 enzyme converts fishy-smelling trimethylamine into another molecule that has no odor. If the enzyme is missing or its activity is reduced because of a mutation 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 strong odor characteristic of trimethylaminuria. Researchers believe that stress and diet also play a role in triggering symptoms.

Read more about the FMO3 gene.

How do people inherit trimethylaminuria?

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

Where can I find information about treatment for trimethylaminuria?

These resources address the management of trimethylaminuria and may include treatment providers.

• Gene Review: Trimethylaminuria

You might also find information on treatment of trimethylaminuria in Educational resources and Patient support.

Where can I find additional information about trimethylaminuria?

You may find the following resources about trimethylaminuria helpful. These materials are written for the general public.

• MedlinePlus - Health informationHealth Topic: Metabolic Disorders
• Additional NIH Resources - National Institutes of HealthNational Human Genome Research Institute
• Educational resources - Information pages (5 links)
• Patient support - For patients and families (3 links)

You may also be interested in these resources, which are designed for healthcare professionals and researchers.

• Gene Reviews - Clinical summary
• Gene Tests - DNA tests ordered by healthcare professionals
• PubMed - Recent literature
• OMIM - Genetic disorder catalog

What other names do people use for trimethylaminuria?

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

See How are genetic conditions and genes named? in the Handbook.

What if I still have specific questions about trimethylaminuria?

• See How can I find a genetics professional in my area? in the Handbook.
• Ask the Genetic and Rare Diseases Information Center.
• Submit your question to Ask the Geneticist.

Where can I find general information about genetic conditions?

The Handbook provides basic information about genetics in clear language.

• What does it mean if a disorder seems to run in my family?
• What are the different ways in which a genetic condition can be inherited?
• If a genetic disorder runs in my family, what are the chances that my children will have the condition?
• Why are some genetic conditions more common in particular ethnic groups?

These links provide additional genetics resources that may be useful.

• Genetics and health
• Resources for Patients and Families
• Resources for Health Professionals

What glossary definitions help with understanding trimethylaminuria?

autosomal ; autosomal recessive ; bacteria ; carrier ; cell ; compound ; depression ; digestive ; digestive system ; egg ; enzyme ; gene ; incidence ; intestine ; kidney ; menstruation ; molecule ; mutation ; protein ; recessive ; sign ; stress ; symptom ; syndrome ; trimethylamine

You may find definitions for these and many other terms in the Genetics Home Reference Glossary.