Overview
Severe primary trimethylaminuria, also known as "fish odor syndrome" or "fish malodor syndrome," is a rare metabolic condition where the body cannot properly break down a chemical called trimethylamine (TMA). TMA is produced in the gut when you digest certain foods, especially those rich in choline, carnitine, and lecithin — such as eggs, fish, liver, and some legumes. Normally, an enzyme in the liver called flavin-containing monooxygenase 3 (FMO3) converts TMA into an odorless form. In people with severe primary trimethylaminuria, this enzyme is missing or works very poorly due to genetic mutations, so TMA builds up in the body and is released through sweat, breath, urine, and other body fluids. This causes a strong, unpleasant body odor often described as smelling like rotting fish. The condition itself does not cause physical pain or organ damage, but the persistent odor can have a devastating impact on a person's emotional well-being, social life, relationships, and mental health. Many people with this condition experience depression, anxiety, social isolation, and low self-esteem. There is currently no cure for severe primary trimethylaminuria. Treatment focuses on managing the odor through strict dietary changes — mainly avoiding foods high in choline and TMA precursors — along with other strategies such as using low-pH soaps, taking certain supplements like activated charcoal or riboflavin (vitamin B2), and sometimes short courses of antibiotics to reduce gut bacteria that produce TMA.
Also known as:
Key symptoms:
Strong fish-like body odorUnpleasant smell in sweatBad-smelling breathFoul-smelling urineOdor that worsens after eating certain foodsOdor that worsens during exercise or stressOdor that may worsen during menstruation in womenDepressionAnxietySocial withdrawal and isolationLow self-esteemDifficulty maintaining relationshipsProblems at school or work due to odor
Clinical phenotype terms (10)— hover any for plain English
Autosomal recessive
Passed on when both parents carry the same gene change; often skips generations
Variable
Can begin at different ages, from infancy through adulthood
Treatments
No FDA-approved treatments are currently listed for Severe primary trimethylaminuria.
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Specialists
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Treatment Centers
8 centersBaylor College of Medicine Rare Disease Center ↗
Baylor College of Medicine
📍 Houston, TX
🏥 NORDStanford Medicine Rare Disease Center ↗
Stanford Medicine
📍 Stanford, CA
🔬 UDNNIH Clinical Center Undiagnosed Diseases Program ↗
National Institutes of Health
📍 Bethesda, MD
🔬 UDNUCLA UDN Clinical Site ↗
UCLA Health
📍 Los Angeles, CA
🔬 UDNBaylor College of Medicine UDN Clinical Site ↗
Baylor College of Medicine
📍 Houston, TX
🔬 UDNHarvard/MGH UDN Clinical Site ↗
Massachusetts General Hospital
📍 Boston, MA
🏥 NORDMayo Clinic Center for Individualized Medicine ↗
Mayo Clinic
📍 Rochester, MN
👤 Mayo Clinic Center for Individualized Medicine
🏥 NORDUCLA Rare Disease Day Program ↗
UCLA Health
📍 Los Angeles, CA
Travel Grants
No travel grants are currently matched to Severe primary trimethylaminuria.
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Caregiver Resources
NORD Caregiver Resources
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Family & Caregiver Grants
Financial assistance programs specifically for caregivers of rare disease patients.
Social Security Disability
Learn how rare disease patients may qualify for SSDI/SSI benefits.
Questions for your doctor
Bring these to your next appointment
- Q1.How severe is my (or my child's) FMO3 enzyme deficiency based on genetic testing results?,Can you refer me to a dietitian who has experience with trimethylaminuria?,What specific foods should I avoid, and how can I make sure I still get proper nutrition?,Are there any supplements like riboflavin or activated charcoal that might help reduce the odor?,Would a short course of antibiotics be appropriate to help manage the odor?,Can you recommend mental health support or a counselor familiar with chronic odor conditions?,Are there any clinical trials or new treatments being studied for this condition?
Common questions about Severe primary trimethylaminuria
What is Severe primary trimethylaminuria?
Severe primary trimethylaminuria, also known as "fish odor syndrome" or "fish malodor syndrome," is a rare metabolic condition where the body cannot properly break down a chemical called trimethylamine (TMA). TMA is produced in the gut when you digest certain foods, especially those rich in choline, carnitine, and lecithin — such as eggs, fish, liver, and some legumes. Normally, an enzyme in the liver called flavin-containing monooxygenase 3 (FMO3) converts TMA into an odorless form. In people with severe primary trimethylaminuria, this enzyme is missing or works very poorly due to genetic mut
How is Severe primary trimethylaminuria inherited?
Severe primary trimethylaminuria follows a autosomal recessive inheritance pattern. Genetic counseling can help families understand recurrence risk and testing options.