Primary trimethylaminuria (TMAU), also known as fish odor syndrome, is a condition where a person has a strong body odor that smells like fish.
This happens because the body lacks an enzyme needed to break down certain compounds, like trimethylamine (TMA). TMA is found in foods like seafood, eggs, cabbage, and beans and has a strong odor. The main symptom of TMAU is a strong fishy smell that comes from sweat, urine, and breath. This odor usually starts in infancy or early childhood and can get worse during puberty. Most people with TMAU have the odor only sometimes, but some might have it all the time. The smell can become stronger during physical activity, stress, or after eating foods rich in choline and lecithin. Hormonal changes, like those during menstruation, menopause, or when taking oral contraceptives, can also make the odor worse.
There is no cure for TMAU, but there are ways to manage the condition. Treatment focuses on reducing the odor and its impact on daily life. This often involves avoiding foods that contain TMA and its precursors, such as milk, eggs, liver, beans, peanuts, soy products, cabbage, broccoli, cauliflower, fish, and shellfish. Other treatments include using odor-neutralizing acidic soaps and lotions, taking vitamin B2 (riboflavin) to boost enzyme activity, and using activated charcoal and copper chlorophyllin supplements to lower TMA levels. Sometimes, low doses of antibiotics may be prescribed to reduce the amount of gut bacteria that produce TMA. Certain medications, such as clozapine, deprenyl, ranitidine, tamoxifen, benzydamine, and sulindac, can make the condition worse, so individuals with TMAU might need to avoid these.
TMAU is caused by pathogenic (disease-causing) variants in the FMO3 gene and exhibits autosomal recessive inheritance. This means that both parents must be carriers to have a 25% chance of having a child with the condition. The risk of being a carrier is based on a person’s ancestry or ethnic background.
Resources:
National Organization for Rare Disorders
Written August 2024
