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Trimethylaminuria
Reviewed by Medicinsk Expert•Last updated: 2026-10-22•Condition

Trimethylaminuria

Trimethylaminuria is a metabolic disorder characterized by the body's inability to break down trimethylamine, resulting in a strong, fish-like body odor.

Overview

Trimethylaminuria is a disorder in which the body is unable to break down trimethylamine, a chemical compound that smells like rotten or decaying fish. As this compound builds up, it is released in sweat, urine, and breath. The odor can interfere with daily life, often affecting relationships, social life, and career, and may lead to depression or social isolation.

Causes

Variants in the FMO3 gene cause trimethylaminuria. This gene provides instructions for making an enzyme that breaks down nitrogen-containing compounds from the diet, such as trimethylamine, which is produced by intestinal bacteria during the digestion of foods like eggs, liver, legumes, and certain fish.

Normally, the FMO3 enzyme converts strong-smelling trimethylamine into an odorless molecule. If the enzyme is missing or its activity is reduced, trimethylamine builds up in the body. Other factors, such as stress, diet, an abnormal increase in trimethylamine-producing bacteria, or liver/kidney disease, can also contribute to symptoms.

Inheritance

Most cases of trimethylaminuria are inherited in an autosomal recessive pattern, meaning both copies of the gene in each cell have variants. Parents of an affected individual typically carry one copy of the altered gene but do not show symptoms. However, carriers of an FMO3 variant may experience mild symptoms or temporary episodes of strong body odor.

Management

While the condition is genetic, researchers believe that stress and diet play a role in triggering symptoms. Temporary symptoms have also been reported in premature infants and in some healthy women at the start of menstruation.

Frequently Asked Questions

Limit high‑trimethylamine precursors such as eggs, liver, kidney, certain fish (e.g., sardines, mackerel), legumes, and cruciferous vegetables (broccoli, cabbage). Emphasize low‑protein, low‑choline foods like rice, pasta, most fruits, and non‑starchy vegetables. Small, frequent meals can reduce bacterial production of trimethylamine in the gut.
Sequencing of the FMO3 gene identifies pathogenic variants and confirms the diagnosis. A homozygous or compound heterozygous result indicates classic trimethylaminuria; heterozygous carriers may have milder, intermittent odor. Family members can be offered carrier testing to understand their risk, especially if they are planning children. Genetic counseling clarifies inheritance patterns and guides reproductive decisions.
Low‑dose riboflavin (vitamin B2) and copper supplements have been reported to modestly increase residual FMO3 activity. Some clinicians prescribe activated charcoal or copper‑containing mouthwashes to bind trimethylamine in the oral cavity. Antibiotics (e.g., metronidazole) may temporarily reduce gut bacteria that produce trimethylamine, but long‑term use is discouraged due to resistance. Always discuss any regimen with a physician.
Stress and hormonal fluctuations can up‑regulate gut bacterial metabolism, increasing trimethylamine production. Practicing stress‑reduction techniques (mindfulness, yoga, regular exercise) and maintaining consistent sleep patterns can blunt spikes. Women may notice worsening odor at the start of menstruation; a short course of low‑dose oral contraceptives or a temporary increase in riboflavin may help, but individual response varies.
Source: MedlinePlus, National Library of Medicine

MedlinePlus brings together authoritative health information from the National Library of Medicine (NLM), the National Institutes of Health (NIH), and other government agencies and health-related organizations.

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