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Trimethylaminuria (TMAU) is a rare disorder of metabolism in which the affected individual is unable to properly break down certain chemicals in the body. The result is the build-up of a chemical called trimethylamine, which is released in the sweat, urine, and breath of people with TMAU. Trimethylamine is the same chemical responsible for the distinctness of fish odor, and so these individuals emit a similar fishy odor. This odor may be constant or may come and go depending on diet and stress. This disease has also been called Fish Odor Syndrome, FMO, or Stale Fish Syndrome.
TMAU is a rare disease, with only about a hundred reported cases in the world. However, not all cases may be correctly diagnosed, and it may be more common than previously thought. Genetic testing has demonstrated 1% of the general population may unknowingly carry one copy of the mutated gene. These people may experience symptoms only when under stress or after eating foods that contain large amounts of trimethylamine or other related substances.
Individuals with TMAU appear normal and healthy. However, they will have an intermittent or constant fishy odor from their sweat, breath, and urine. This smell is poorly concealed by washing or application of perfumes and deodorants. Their symptoms may worsen during times of stress, diet changes, around menstruation or menopause, or while taking oral contraceptives. Children and their parents may be reported for poor hygiene by schools or workplaces. Affected individuals often experience a large amount of social ostracizing or isolation as a result of this odor. Some researches believe that high amounts of trimethylamine can also cause psychiatric symptoms (such as depression) and seizures.
The majority of TMAU cases are caused by a genetic mutation in a gene called mono-oxygenase 3 (FMO3). This gene is responsible for the break down of trimethylamine into other compounds which have no odor. People missing FMO3 cannot break down trimethylamine and as a result generate the odor that comes from an excessive amount of this substance. This gene is inherited in an autosomal recessive fashion, meaning that both parents have one mutated gene and one normal gene, and as a result they experience mild to no symptoms. Their child, however, has a 25% chance of inheriting two mutated genes and therefore experience more severe symptoms. It is important to note that the parents did not cause this mutation to occur.
The majority of reported cases have been genetic in nature. However, there are some reported cases of TMAU developing in patients with liver or kidney disease, or in patients being treated with a large amount of a substance called L-carnitine (levocarnitine). In these cases, the affected individual may not have enough enzyme to fully breakdown the high amounts of trimethylamine in their blood.
Because this disease is not well known, it often takes many years before it is diagnosed. The only way to diagnose TMAU is by measuring the levels of trimethylamine in the urine. This test can also be used to identify carriers of TMAU-someone who carries one copy of the mutated gene but does not have the symptoms. Parents of children with TMAU may wish to speak with a genetic counselor to consider testing to determine the risk of having another child with TMAU.
Unfortunately, there is currently no cure for TMAU. Evidence suggests that following a special diet may decrease the severity of the odor produced. By limiting the amount of choline (high in fish, eggs, beans, and organ meats) and lecithin (high in eggs, soybean, and corn), individuals may experience decreased symptoms. Some individuals have found that increasing greens, like parsley, may also help decrease the odor. Low doses of antibiotics to kill bacteria in the digestive system may temporarily reduce odor, but is not an effective long-term treatment. Symptoms of TMAU also seem to worsen with stress and excessive sweating, so taking measures to stay cool and relaxed may also alleviate the odor. Perfumes, soaps, shampoos, deodorants, and other products designed to decrease body odor seem to have little lasting effect on individuals with TMAU. Children with TMAU may experience emotional problems like depression and may even become suicidal, so it is important to connect with a therapist or psychiatrist if these symptoms develop.
Some children with TMAU will have improvement in symptoms as they get older, but the reasons why are not well understood. For most of people with TMAU, their symptoms are life-long. No other organ systems are involved, and there is no limitation on their physical activity. People with TMAU are able to live to a normal lifespan. The most profound obstacle in their lives is dealing with the social and psychological aspects of the disease.
Connect with other parents
In the spirit of community and support, Madisons Foundation offers the unique service of connecting parents of children with rare diseases. If you would like to be connected to other
parents of children with this disease, please fill out this brief form.
WAPD knowledge base
The personal testimony of an individual with TMAU with tips for dealing with the symptoms and the social pressures.
Online Mendelian Inheritance in Man
An electronic catalog of human genes and genetic disorders, developed by the National Center for Biotechnology Information. The language on this page about Trimethylaminuria is technical, but is considered to be a very comprehensive source of information.
What's That Smell?
Modern science puts its mark on a rare but ancient body-odor disease. This in an article about Trimethylaminuria, written by Damaris Christensen and published by ScienceNewsOnline, Volume 155, number 20 (May 15, 1999).
This site is dedicated to providing information, aid and support for persons afflicted with TMAU.
Online support group for individuals with TMAU
An excellent online resource for people with TMAU
NIH Patient Support
Information specifically designed for patients and families
CLIMB (Children Living with Inherited Metabolic Diseases)
A good source of resources for patients with metabolic disease
Genetic and Rare Diseases (GARD) Information Center
A website with contact information for genetic specialists.
References and Sources
Medline: www.ncbi.nlm.nih.gov/entrez/dispomim.cgi?id=602079, keyword "trimethylaminuria"
OMIM: www.ncbi.nlm.nih.gov, disease #602079 National Human Genome Research Institute: www.genome.gov/11508983