Trimethylaminuria (TMAU), also known as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder that causes a defect in the normal production of the enzyme Flavin containing monooxygenase 3 (FMO3). When FMO3 is not working correctly or if not enough enzyme is produced, the body loses the ability to properly break down trimethylamine (TMA) from precursor compounds in food digestion into trimethylamine oxide (TMAO) through a process called N-oxygenation. Trimethylamine then builds up and is released in the person's sweat, urine, and breath, giving off a strong fishy odor or strong body odor.

Symptoms

Trimethylamine builds up in the body of patients with trimethylaminuria. The trimethylamine gets released in the person's sweat, urine, reproductive fluids, and breath, giving off a strong fishy or body odor. Some people with trimethylaminuria have a strong odor all the time, but most have a moderate smell that varies in intensity over time. Individuals with this condition do not have any physical symptoms, and typically appear healthy.

The condition seems to be more common in women than men, for unknown reasons. Scientists suspect that female sex hormones, such as progesterone and/or estrogen, aggravate symptoms. There are several reports that the condition worsens around puberty. In women, symptoms can worsen just before and during menstrual periods, after taking oral contraceptives, and around menopause.

This odor varies depending on many known factors, including diet, hormonal changes, stress level, amount of sweat, other odors in the space, and individual sense of smell.

Treatment

Currently, there is no known cure or treatment for the disorder. However, some people affected by the disorder live relatively normal lives by managing their symptoms and with counseling. When the condition is suspected or known to occur in a family, genetic testing can be helpful in identifying the specific individuals who have or carry the disorder.

Ways of reducing the fishy odor may include:

Avoiding foods such as egg yolks, legumes, red meats, fish, beans and other foods that contain choline, carnitine, nitrogen, sulfur and lecithin
Taking low doses of antibiotics such as neomycin and metronidazole in order to reduce the amount of bacteria in the gut
Using slightly acidic detergent with a pH between 5.5 and 6.5
Additionally, at least one study has suggested that daily intake of the supplements activated charcoal and/or copper chlorophyllin may improve the quality of life of individuals afflicted with TMAU by helping their bodies to oxidize and convert TMA to the odorless N-oxide (TMAO) metabolite. Study participants experienced subjective reduction in odor as well as objective reduction in TMA and increase in TMAO concentration measured in their urine. The study's success rates varied:
85% of test participants experienced complete loss of detectable "fishy" odor
10% experienced some reduction in detectable odor
5% did not experience any detectable odor reduction