What Is Fish Odor Syndrome Or Trimethylaminuria?

Imagine having to smell like rotten fish your whole life. Now imagine you smelling that foul and being unable to hide the stench with perfumes, sprays or deodorants. Most of us would probably lose our minds, right? After all, smelling like fish is probably the fastest way to get bullied at school and ostracized at work. But according to the experts, people who face these problems on a daily basis actually exist, and the disorder that causes the foul-smelling odor is called Trimethylaminuria, better known as the fish odor syndrome.

Fish Odor Syndrome

What Is The Fish Odor Syndrome?

Fish Odor Syndrome is a very rare genetic disease where the body is unable to metabolize the chemical known as trimethylamine. According to the experts, trimethylamine gives off an overpowering odor that is considered to be even worse than rotten fish. Typically, the body’s natural metabolism converts trimethylamine, getting rid of the chemical that smells.

When someone has Trimethylaminuria, the chemical builds up in the body, emitting the fishy odor from the person’s breath, sweat and urine. This smell can cause severe problems to children, teenagers, and adults with Trimethylaminuria due to the lack of information and diagnosis on the disease as well as the intolerance of other people who want to distance themselves from the smell.

What Are The Different Forms Of Trimethylaminuria?

There are two main forms of this disease:

  • The Primary Form: Is caused by an autosomal recessive trait in the gene which causes a defect in which the production of the enzyme flavin-containing monooxygenase 3 (FMO3) is prevented, leading to the failure of the metabolism of trimethylamine.
  • The Secondary Form: Is caused by a side effect when someone has large doses of choline. This form of trimethylaminuria occurs because a large amount of choline is converted into excess amounts of trimethylamine, leading to the fishy smell.

How Is Trimethylamine Normally Processed?

Usually, trimethylamine is produced when the enzyme flavin-containing monooxygenase 3 (FMO3) works as a catalyst in the liver to convert choline and/or carnitine via the biochemical process of metabolism to trimethylamine N-oxide, which is said to be odorless. Foods that contain choline include wheat germ, kidney beans, liver, soy, egg yolk and brewer’s yeast.

What Are The Symptoms Of The Fish Odor Syndrome?

As the name suggests, this disorder causes a strong fish odor to be emitted by the person’s breath, urine, and sweat. Other than this undeniable sign, the person with Trimethylaminuria is usually otherwise healthy and normal.

For those who have a secondary form of Trimethylaminuria, reducing the dosage of choline, lecithin or L-carnitine will reduce trimethylamine levels, alleviating the symptoms of the disorder.

According to experts, choline is said to be used to treat Alzheimer’s disease and Huntington disease while L-carnitine is prescribed to people suffering from carnitine deficiency. L-carnitine is also used by some bodybuilders as it’s assumed that this raises muscle mass and strength.

What Causes Fish Odor Syndrome?

The primary form of Trimethylaminuria is caused by an autosomal recessive genetic trait that prevents metabolism of trimethylamine. Most people with the fish odor syndrome have the same genetic mutation of FMO3 from both parents.


The particular gene that causes this disease has been identified and designated as FMO3 gene.

The secondary form of Trimethylaminuria is caused when high doses of L-carnitine, choline, or lecithin are taken, leading to the inhibition of the enzyme flavin-containing monooxygenase 3 (FMO3) in the liver metabolizing trimethylamine.

How Many People Have Been Affected By The Fish Odor Syndrome?

This disease is a very rare disorder with little more than 100 cases being documented till date. However, it is assumed that many more cases have been under-diagnosed or misdiagnosed by doctors.

How Is Trimethylaminuria Diagnosed?

While the odor may be a sign of someone with a severe case of Trimethylaminuria, it can be inaccurate for those with milder cases of the disorder. For the most accurate results, doctors recommend performing a urine analysis which diagnoses the concentration of trimethylamine and trimethylamine N-oxide in the body. To distinguish the primary and secondary forms of Trimethylaminuria, doctors can also recommend genetic testing.

Genetic Testing

Fish Odor Syndrome Treatment:

If you have secondary Trimethylaminuria, you can stop taking the high doses of choline and lecithin to eliminate the bad odor and Trimethylaminuria. For those with mild cases of primary Trimethylaminuria, reducing consumption of foods with lecithin and choline can help reduce the symptoms.

For those with severe cases of the fish odor syndrome, doctors can prescribe a gut-sterilizing antibiotic which reduces the bacteria that convert trimethylamine N-oxide and choline into trimethylamine. Activated charcoal or copper chlorophyllin in supplements have also shown to bind with trimethylamine, reducing the odor emitted.

Modified on
About Michelle 59 Articles