Trimethylaminuria: Definition, Causes, Symptoms, Diagnosis and Treatment

Also known as fish odor syndrome, it is a rare genetic disorder in which the body cannot process a compound called trimethylamine.

This chemical is found in many food products and is normally absorbed by the body and eliminated, but in some people this ability to process or absorb trimethylamine is absent, causing the chemical to be eliminated from the body through sweat, breath, and urine giving a pungent odor that is similar to that of a rotten fish or garbage.

Fish smell syndrome or trimethylaminuria can become quite embarrassing for people, especially those who go out to work and other social activities.

Trimethylaminuria tends to be worse in women at the time of their menstrual periods. Trimethylamine is abundant in choline-rich foods such as eggs, wheat, and certain meats. The best way to prevent fish odor syndrome or trimethylaminuria is to eat less of foods high in choline and foods that are low in calories.

Causes of trimethylaminuria

The cause of trimethylaminuria syndrome can be better understood if we understand a little about the body’s digestive system. There are quite a few bacteria present in the stomach that help digest foods like eggs, beans, and other shellfish that are rich in choline. During this digestion process, they release a chemical called trimethylamine.

Under normal circumstances, this trimethylamine is converted to odorless trimethylamine oxide by an enzyme found in the liver called FMO3.

Most people have the gene called FMO3 that helps in the production of the enzyme FMO3, but in some cases this gene is completely absent or defective and unable to function properly, allowing a gradual accumulation of trimethylamine in the body.

This results in trimethylamine being released from the body through urine, sweat, and breathing, resulting in fishy odor syndrome or trimethylaminuria. In most cases of trimethylaminuria, the faulty FMO3 gene is inherited from both parents.

There are also other causes of trimethylaminuria. These causes are the presence of certain proteins in excess or an increase in the bacteria in the stomach that produces trimethylamine. Some cases of fish odor syndrome or trimethylaminuria have been linked to kidney or liver dysfunction that results in the FMO3 enzyme not working properly.

Women are more likely to have trimethylaminuria than men since women’s sex hormones tend to aggravate symptoms.

Fish smell syndrome or trimethylaminuria in women is usually worse around menstrual periods, when taking a birth control pill, or around menopause. Furthermore, stress and unhealthy diet have also been a cause for the development of fish smell syndrome or trimethylaminuria.


Besides having a strong pungent odor in sweat, urine, saliva, and certain vaginal fluids, there are no additional symptoms caused by fish odor syndrome or trimethylaminuria. The intensity of the odor can vary and at times the affected person may have a very strong odor, but at other times they tend to have a much milder odor.

The smell of fish odor syndrome or trimethylaminuria usually begins in childhood and begins to manifest slowly, although in some cases it has also started in adulthood. In some children, trimethylaminuria may be temporary and gradually as the child grows, the odor slowly disappears.

Diagnosis of trimethylaminuria

Trimethylaminuria is usually diagnosed through a urinalysis that measures the amount of trimethylamine and trimethylamine oxide in the body. If the level of trimethylamine is higher than trimethylamine oxide, the diagnosis of fish odor syndrome or trimethylaminuria is confirmed.

This test is usually done after giving the patient foods rich in choline for the best result to diagnose fishy odor syndrome or trimethylaminuria. In some cases, genetic testing may also be done to see if there are abnormalities in the FMO3 gene that cause trimethylaminuria.


There is currently no definitive treatment for trimethylaminuria except for certain lifestyle and diet changes. There are also certain medications that can be prescribed to reduce the amount of trimethylamine in the body.

Some of the diet and lifestyle changes that can be made for fish odor syndrome or trimethylaminuria are:

Avoid foods rich in choline such as cow’s milk, eggs, liver, peas, beans, peanuts, broccoli, cabbage, cauliflower, and shellfish. Consultation with a nutritionist or dietitian who can formulate a diet plan for the patient with less choline-containing foods is recommended for women who are pregnant or planning to become pregnant.

Taking low doses of antibiotics can help kill the bacteria that make up trimethylamine from the stomach, resulting in less build-up of trimethylamine in the body and thus reducing the symptoms of fish odor syndrome or trimethylaminuria.

It should be noted here that antibiotics should be taken in small doses and for a short period of time to avoid antibiotic resistance. Also, one can use laxatives to speed up bowel movements so that there is less trimethylamine in the body to help with trimethylaminuria.

There are also certain lifestyle measures that one can incorporate into the daily routine, such as exercising with less weight, so that there is less amount of sweat produced to help with the symptoms of trimethylaminuria.

Fish smell syndrome or trimethylaminuria can be an embarrassing condition for many people and can lead to depression and social isolation. This is where counseling from a psychologist can go a long way in helping patients cope with the symptoms of fish odor syndrome.