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 usually absorbed by the body and eliminated. Still, 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 embarrassing for people, especially those who go out to work and other social activities.

Trimethylaminuria tends to be worse in women during 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 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 produce the enzyme FMO3. Still, in some cases, this gene is absent or defective and unable to function correctly, 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 specific proteins in excess or an increase in the stomach bacteria that produce 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 correctly.

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, taking a birth control pill, or around menopause. Furthermore, stress and an unhealthy diet have also been a cause of 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 powerful smell, but at other times they tend to have a much milder aroma.

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 body’s amount of trimethylamine and trimethylamine oxide. 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 no definitive treatment for trimethylaminuria except for particular lifestyle and diet changes. Certain medications 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 choline-rich foods 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 pregnant women or planning to become pregnant.

Taking low doses of antibiotics can help kill the bacteria that makeup 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 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 specific lifestyle measures that one can incorporate into the daily routine, such as exercising with less weight so that less amount of sweat is produced to help with the symptoms of trimethylaminuria.

Fish smell syndrome or trimethylaminuria can be an embarrassing condition for many people and 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.