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Trimethylaminuria (TMAU), also known as fish odor syndrome or fish malodor syndrome[1], is a rare metabolic disorder that causes a defect in the normal production of the enzyme Flavin containing monooxygenase 3 (FMO3).[2][3] When FMO3 is not working correctly or if not enough enzyme is produced, the body loses the ability to properly breakdown trimethylamine (TMA) from precursor compounds in food 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.
The first clinical case of TMAU was described in 1970 in the medical journal The Lancet,[4] but literary references go back more than a thousand years. Shakespeare’s Tempest describes the outcast Caliban, “He smells like a fish; a very ancient and fish-like smell…”. Hindu folklore mentions in the epic Mahabharata (compiled around 400 AD) a maiden who “grew to be comely and fair, but a fishy odor ever clung to her.”
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 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.[5]
The condition seems to be more common in women than men, but scientists don’t know why. 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.[5]
This odor varies depending on many known factors, including diet, hormonal changes, other odors in the space, and individual sense of smell.
TMAU is a life-disruptive disorder caused by both genetic and environmental factors. Living with TMAU is challenging, and it can adversely affect the livelihood of adults who have it and their families. Children with the condition could face rejection or a lack of understanding from peers during school or at play. There are various online support groups that have been created to help those in with malodor issues such as TMAU. The Yahoo TMAU support group [1] is listed in the National Institute of Healths publication “Learning About Trimethylaminuria” [2].
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