Short answer · Medically reviewed summary · Last updated: 2026-05-08

Trimethylaminuria is a rare metabolic disorder characterized by an impaired ability to break down the compound trimethylamine, leading to the excretion of a strong, fishy body odor in sweat, urine, and breath. This condition is primarily caused by mutations in the FMO3 gene, which prevents the body from converting volatile trimethylamine into odorless trimethylamine N-oxide. What is the underlying mechanism of Trimethylaminuria? In a healthy individual, the liver produces an enzyme called flavin-containing monooxygenase 3 (FMO3) that breaks down trimethylamine.

What is Trimethylaminuria

Name: What is Trimethylaminuria
Creator: DiseaseMaps Editorial Team
Published: 2016-05-26UTC06:32:09.0000000

What is Trimethylaminuria? Plain-language, medically reviewed definition plus the lived reality told by patients.

Trimethylaminuria is a rare metabolic disorder characterized by an impaired ability to break down the compound trimethylamine, leading to the excretion of a strong, fishy body odor in sweat, urine, and breath. This condition is primarily caused by mutations in the FMO3 gene, which prevents the body from converting volatile trimethylamine into odorless trimethylamine N-oxide.

What is the underlying mechanism of Trimethylaminuria?

In a healthy individual, the liver produces an enzyme called flavin-containing monooxygenase 3 (FMO3) that breaks down trimethylamine. People living with Trimethylaminuria possess a deficiency or dysfunction in this enzyme. As a result, trimethylamine accumulates in the body and is released through bodily fluids. While 34 members of the DiseaseMaps.org community have shared their experiences, it is important to note that the condition is often underdiagnosed due to the subjective nature of odor reporting.

Is Trimethylaminuria hereditary?

Yes, Trimethylaminuria is typically inherited in an autosomal recessive pattern. This means an individual must inherit two copies of the mutated FMO3 gene—one from each parent—to manifest the primary form of the condition. Carriers of a single mutation are generally asymptomatic.

What are the primary classifications and symptoms?

Trimethylaminuria is generally classified into two categories based on its origin:

Primary Trimethylaminuria: Caused by genetic mutations in the FMO3 gene.

Secondary Trimethylaminuria: Triggered by excessive intake of dietary precursors (like choline or carnitine) or liver/kidney dysfunction that overwhelms normal enzyme capacity.

Who is typically affected by Trimethylaminuria?

The prevalence of Trimethylaminuria remains unknown, though it is considered a very rare metabolic disorder. Symptoms may be present from birth or emerge after puberty, often fluctuating in intensity. Hormonal changes, stress, and dietary choices are known to influence the severity of the odor associated with Trimethylaminuria. Unlike many other metabolic disorders, it does not typically cause physical organ damage, though the psychological impact can be significant.