Table of Contents

Trimethylaminuria (TMAU) a.k.a. Fish Odor Syndrome

What is trimethylaminuria?

Trimethylaminuria is a rare metabolic disorder that occurs when the body is unable to break down certain nitrogen-containing compounds such as trimethylamine; trimethylamine has a fishy odor and is produced in the intestines when certain types of food (i.e. eggs, liver, fish and some vegetables) are digested. Affected individuals do not have other health problems related to the condition, but the unpleasant odor can result in social and psychological problems. Trimethylaminuria seems to be more common in women.

What are the symptoms of trimethylaminuria?

Trimethylaminuria is characterized primarily by a fishy odor that occurs when excess trimethylamine is released in the person’s sweat, urine, reproductive fluids, and breath. Although some affected people may have a constant strong odor, most have a moderate odor that can vary in intensity. Factors that promote sweating, such as exercise, stress, and emotional upsets, may also worsen the odor. Affected people typically do not have any additional signs and symptoms and appear healthy. However, the odor can interfere with many aspects of daily life, leading to social and psychological problems.

What causes trimethylaminuria?

Most cases of trimethylaminuria are caused by mutations in the FMO3 gene. This gene provides the body with instructions to make an enzyme that is responsible for breaking down certain nitrogen-containing compounds such as trimethylamine. This mutation in this gene prevents the enzyme from working properly, so it is unable to break down compounds like trimethylamine. As trimethylamine begins to build up in the body, it is released in a person’s sweat, urine, and breath. Trimethylamine has that fishy odor.

How is trimethylaminuria diagnosed?

A diagnosis of trimethylaminuria is often suspected based on the presence of characteristic signs and symptoms (odor). A urine test and genetic testing can then be ordered to confirm the diagnosis.

What are the treatments for trimethylaminuria?

Although there is no cure for trimethylaminuria, the following are some ways to reduce symptoms of odor:
  • Avoidance of foods that contain trimethylamine and its precursors (choline, lecithin, and trimethylamine N-oxide).
    • Trimethylamine is present in high levels in milk obtained from wheat-fed cows.
    • Choline is present in high amounts in: eggs, liver, kidney, peas, beans, peanuts, soy products, brussels sprouts, broccoli, cabbage, and cauliflower.
    • Trimethylamine N-oxide is present in seafood
  • Low doses of antibiotics
  • Laxatives can decrease the amount of time food remains in the intestines and therefore reduce the amount of trimethylamine made
  • Nutritional supplements (activated charcoal and copper chlorophyllin) can decrease the concentration of trimethylamine in the urine
  • Soaps with a moderate pH (between 5.5 and 6.5) can help remove the secreted trimethylamine from the skin
  • Riboflavin (vitamin B2) supplements can enhance any existing FMO3 enzyme activity (which breaks down trimethylamine)
  • Avoidance of exercise, stress, emotional upsets, and other factors that can promote sweating

Where can I find out more about trimethylaminuria?

Trimethylaminuria (TMAU) a.k.a. Fish Odor Syndrome Articles