The following information may help to address your question:
What is trimethylaminuria?
is a metabolic disorder
that occurs when the body is unable to break down certain nitrogen-containing compounds such as trimethylamine. Trimethylamine, which has a fishy odor, is produced in the intestines when certain types of food (i.e. eggs, liver, legumes, fish and some vegetables) are digested. As trimethylamine begins to accumulate in the body, it is released in the sweat, urine, reproductive fluids, and breath. This leads to the characteristic odor of trimethylaminuria. Affected individuals are normal and healthy; however, the unpleasant odor often results in social and psychological problems. This condition is caused by changes (mutations
) in the FMO3
gene and is inherited in an autosomal recessive
manner. Although there is no cure, trimethylaminuria can often be managed by reducing the amount of trimethylamine in the body. For example, affected people can modify their diet to avoid foods with high levels of trimethylamine.
Last updated: 9/6/2016
What are the signs and 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. For example, the odor may be more severe just before and during menstruation in women. 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.
Last updated: 3/25/2015
What causes trimethylaminuria?
Most cases of trimethylaminuria are caused by changes (mutations
) in the FMO3
gene. This gene encodes an enzyme
that is responsible for breaking down certain nitrogen-containing compounds such as trimethylamine. Trimethylamine is produced in the intestines when certain types of food (i.e. eggs, liver, legumes, fish and some vegetables) are digested. A 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. Because trimethylamine has a fishy odor, this leads to the characteristic features of trimethylaminuria.
Last updated: 9/6/2016
How is trimethylaminuria inherited?
Trimethylaminuria is usually inherited in an autosomal recessive
This means that to be affected, a person must have a mutation
in both copies of the responsible gene
in each cell. The parents of an affected person usually each carry one mutated copy of the gene and are referred to as carriers. Carriers typically do not show signs or symptoms of the condition, although carriers of trimethylaminuria may experience mild symptoms or have temporary episodes of fish-like odor.
When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) risk to have the condition, a 50% (1 in 2) risk to be a carrier like each of the parents, and a 25% chance to not have the condition and
not be a carrier.
Last updated: 9/6/2016
How is trimethylaminuria diagnosed?
A diagnosis of trimethylaminuria is often suspected based on the presence of characteristic signs and symptoms. A urine test and/or genetic testing can then be ordered to confirm the diagnosis. The urine test measures the level of trimethylamine in the urine when the person is on a non-restricted diet or following a choline challenge (a person is given a dose of choline by mouth prior to the test). People with trimethylaminuria have elevated levels of trimethylamine in the urine.
Genetic testing is available for FMO3
, the gene known to cause trimethylaminuria.
Carrier testing for at-risk relatives and prenatal testing are possible if the disease-causing mutations in the family are known.
GeneReviews offers more specific information about the diagnosis of trimethylaminuria. To access this resource, please click here
Last updated: 10/4/2016
How might trimethylaminuria be treated?
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. This decreases the amount of trimethylamine that is made by bacteria in the intestines
- Laxatives can decrease the amount of time food remains in the intestines and 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
- 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
People with trimethylaminuria may also find the following to be helpful:
- Behavioral counseling to help with depression and other psychological symptoms
- Genetic counseling to better understand how they developed trimethylaminuria and the risks of passing the condition on to their children
: People should follow the treatment advice of their healthcare provider and should not attempt to self-administer these treatment approaches. Medications and supplements can have unintended interactions, and dietary restrictions can result in nutritional deficits.
Last updated: 3/26/2015
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