Fish odor syndrome (trimethylaminuria) facts*
*Fish odor syndrome (trimethylaminuria) facts Medically Edited by:
Charles P. Davis, MD, PhD
- Fish odor syndrome (trimethylaminuria) is a genetic disease; symptoms are
often present from birth.
- Fish odor syndrome is characterized by an offensive body odor and the smell
of rotting fish due to the excessive excretion of trimethylaminuria (TMA) in the
urine, sweat, and breath of affected individuals.
- Fish odor syndrome is caused by mutations in the FMO3 gene.
- Other causes of odor body can occur as a result from an excess of proteins
in the diet, or from an increase in bacteria that normally produce
trimethylamine in the GI tract (also may make fish odor syndrome worse);
disease, kidney disease, poor hygiene,
gingivitis, and cases of blood-borne
halitosis. Diagnostic tests that help differentiate fish odor syndrome
(trimethylaminuria) from other causes of body odor are available at specialized
- Fish odor syndrome symptoms have been seen temporarily in a small number of
premature infants and in healthy women at the start of menstruation, usually in
individuals that are heterozygous for the mutant FMO3 gene or due to immaturity
of the faulty FMO3 gene expression (FMO3 expression increases with age).
- Fish odor syndrome treatment includes certain dietary restrictions, use of
acid lotions and soaps to remove secreted trimethylamine on the skin, use of
activated charcoal and copper chlorophyllin, certain antibiotics, laxatives, and
What is fish odor syndrome (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
What are the signs and symptoms of fish odor syndrome (trimethylaminuria)?
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.
What causes fish odor syndrome (trimethylaminuria)?
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
How common is fish odor syndrome (trimethylaminuria)?
Trimethylaminuria is an uncommon genetic disorder; its incidence is unknown.
What genes are related to fish odor syndrome (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.
How do people inherit fish odor syndrome (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.
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Where can I find information about diagnosis, management, or treatment of
These resources address the diagnosis or management of trimethylaminuria and
may include treatment providers.
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 –
Genetic and Rare Diseases Information Center
– Information about genetic conditions and rare
- Additional NIH Resources – National Human Genome Research Institute
You may also be interested in these resources, which are designed for
healthcare professionals and researchers.
- Gene Reviews
Gene Tests – DNA
tests ordered by healthcare professionals
- OMIM – Genetic
What other names do people use for trimethylaminuria?
- Fish malodor syndrome
- Fish odor syndrome
- Stale fish syndrome