Trimethylaminuria

Trimethylaminuria is a disorder in which the body is unable to break down trimethylamine, a compound derived from the diet that has a strong odor of rotting fish. As trimethylamine builds up in the body, it causes affected people to give off a fish-like odor in their sweat, urine, and breath. The intensity of this odor may vary over time. In many cases, the strong body odor interferes with an affected person's relationships, social life, and career. People with trimethylaminuria may experience depression and social isolation as a result of this condition. more...

Diagnosis

The only test for trimethylaminuria at this time is a urine test for elevated levels of trimethylamine.

A similar test can be used to identify carriers of this condition - those individuals who carry one copy of a mutated gene but do not have symptoms. In this case, the person would be given a high dose of choline (one of the precursors of trimethylamine) and then have their urine tested for elevated levels of trimethylamine.

Treatment

Although there is no cure for trimethylaminuria, it is possible for people with this condition to live normal, healthy lives without the fear of being shunned because they smell like rotten fish. Ways of reducing the odor include:

• Avoiding foods containing choline and trimethylamine-oxide, the precursors of trimethylamine.
• Taking low doses of antibiotics to reduce the amount of bacteria in the gut.
• Using soaps with a moderate pH, between 5.5 and 6.5.

Also helpful are:

• Behavioral counseling to help with depression and other psychological symptoms.
• Genetic counseling to better understand how they developed the condition and to be aware of the risks of passing it on to the next generation.

Genetics

Most cases of trimethylaminuria appear to be inherited in an autosomal recessive pattern, which means two copies of the gene in each cell are altered. Most often, the parents of an individual with an autosomal recessive disorder are carriers of one copy of the altered gene. Carriers may have mild symptoms of trimethylaminuria or experience temporary episodes of fish-like body odor.

Mutations in the FMO3 gene cause trimethylaminuria. The FMO3 gene makes an enzyme that breaks down nitrogen-containing compounds from the diet, including trimethylamine. This compound is produced by bacteria in the intestine as they digest proteins from eggs, meat, soy, and other foods. Normally, the FMO3 enzyme converts fishy-smelling trimethylamine into another molecule that has no odor. If the enzyme is missing or its activity is reduced because of a mutation in the FMO3 gene, trimethylamine is not broken down and instead builds up in the body. As the compound is released in a person's sweat, urine, and breath, it causes the strong odor characteristic of trimethylaminuria. Researchers believe that stress and diet also play a role in triggering symptoms.

Although FMO3 mutations account for most known cases of trimethylaminuria, some cases are caused by other factors. A fish-like body odor could result from an excess of certain proteins in the diet or from an increase in bacteria that normally break down trimethylamine in the digestive system. A few cases of the disorder have been identified in adults with liver damage caused by hepatitis. Temporary symptoms of trimethylaminuria have also been reported in a small number of premature infants and in some healthy women at the start of menstruation.

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