Fishy Odor Syndrome (Trimethylaminuria): Causes, Symptoms, Diagnosis, and Treatment

Trimethylaminuria, also known as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder characterized by a strong, unpleasant body odor reminiscent of rotting fish. 

A person with this condition may emit a strong, unpleasant fishy odor from their body fluids, including breath, urine, and sweat. 

The smell is often so potent that others may find it difficult to remain in the same room as the affected person, who is usually unaware of their own odor.

This condition can significantly impact quality of life, causing social and psychological distress. 

What are the causes, symptoms, diagnosis and management of trimethylaminuria?

Understanding the Causes of Fishy Odor Syndrome

Inherited defect in the FMO3 gene

The primary cause of fish odor syndrome is an inherited defect in the FMO3 gene, which codes for the enzyme flavin-containing monooxygenase 3 (FMO3).

This enzyme is responsible for converting odorous trimethylamine, produced by gut bacteria from dietary sources like choline and carnitine, into non-odorous trimethylamine N-oxide. 

When FMO3 is deficient or nonfunctional, trimethylamine accumulates in the body and is excreted in sweat, breath, urine and other bodily secretions, resulting in the characteristic fishy smell.

Acquired trimethylaminuria: Medications, vitamin deficiencies, and other factors

In some cases, trimethylaminuria can be acquired due to certain medications (like antidepressants and chemotherapy drugs), vitamin B2 deficiency, liver or kidney disease, and gut dysbiosis. 

Dietary factors, such as high intake of marine fish, eggs, offal and legumes, may also exacerbate symptoms by increasing trimethylamine precursor load.

Recognizing the Symptoms of Trimethylaminuria

The hallmark symptom of trimethylaminuria is a strong body odor resembling rotting fish, which can be constant or episodic.

Other signs and symptoms may include:

  • Foul-smelling breath, sweat and urine
  • Unpleasant taste in the mouth
  • Gastrointestinal issues like nausea, vomiting and abdominal pain
  • Social isolation, low self-esteem and depression due to embarrassment and stigma

Interestingly, affected individuals often cannot detect their own odor, relying on family and friends to alert them. 

Symptoms may worsen during puberty, menstruation, stress, exercise, and after consuming trigger foods. 

Infants with trimethylaminuria may exhibit a “sweaty feet” smell and failure to thrive.

Diagnosing Trimethylaminuria: Tests and Challenges

Prompt diagnosis is crucial for initiating appropriate management and support. However, trimethylaminuria is frequently misdiagnosed or underdiagnosed due to lack of awareness among healthcare providers.

The gold standard diagnostic test involves a urine trimethylamine/trimethylamine N-oxide ratio, which is elevated in affected individuals. 

This specialized assay is currently available only at select biochemical genetics laboratories like the Research Centre for Medical Genetics in Moscow

Genetic testing for FMO3 mutations can provide a definitive diagnosis in suspected cases.

Effective Management Strategies for Trimethylaminuria

While there is no cure for primary trimethylaminuria, dietary modifications and lifestyle changes can significantly reduce fishy odor and improve symptoms. 

The mainstay of management includes:

  • Low-choline, low-trimethylamine diet: Avoiding or limiting high-choline foods like eggs, liver, beans, peanuts, soy, seafood, and cruciferous vegetables. Working with a knowledgeable dietitian to ensure nutritional adequacy is recommended.
  • Supplementation: Taking activated charcoal or copper chlorophyllin supplements with meals may help neutralize trimethylamine in the gut. Riboflavin (vitamin B2) supplements can enhance residual FMO3 activity in some patients.
  • Odor-reducing strategies: Using pH-balanced soaps and antiperspirants, washing clothes frequently, and maintaining good oral hygiene. Avoiding stress, heat and humidity when possible.
  • Gut health optimization: Promoting a balanced gut microbiome through probiotic foods and supplements. Addressing any underlying gastrointestinal issues.
  • Medications: In severe cases, short-term use of antibiotics like metronidazole to suppress trimethylamine-producing bacteria, or sequestering agents like cholestyramine, may be considered under medical supervision.

Coping with Trimethylaminuria: Support, Resources, and Advocacy

Coping with the physical, emotional and social challenges of trimethylaminuria can be overwhelming.

Online support groups and resources for patients and families

Fortunately, there are resources and support networks available for affected individuals and their families:

Specialized care and support in Russia

Specialized care and support in Ukraine

Empowering Patients to Live Well with Trimethylaminuria

By empowering patients with knowledge, strategies and support, living well with trimethylaminuria is possible.

If you suspect that you or a loved one may have symptoms consistent with this condition, seek evaluation from a healthcare provider specializing in metabolic disorders. 

With prompt diagnosis, personalized management and a strong support system, the fishy odor of trimethylaminuria need not define one’s identity or limit one’s potential.

About the Author

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Tetiana Melnyk is a healthcare journalist at Mister Blister specializing in legal and regulatory analysis of Ukraine's healthcare sector. A medical graduate of Vinnitsa National University, Tetiana leverages her background as a practicing physician to provide insightful, critically-examined coverage. Her expertise stems from hands-on clinical work across Kyiv and medical research experience.

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