Trimethylaminuria (Fish Odor Syndrome or TMAU)

What are the symptoms of trimethylaminuria?

People with TMAU give off an unpleasant nauseating odor that people describe as smelling like rotten fish. The odor may be body odor, bad breath (halitosis) or strong-smelling pee.

Sometimes, people only notice TMAU symptoms when the person who has the condition sweats or is experiencing stress. But some people with trimethylaminuria carry such a strong scent that others notice the scent just from being in the same room, standing across a counter or sitting in the same section of a bus or train.

What causes TMAU?

Trimethylaminuria happens when something affects the FMO3 enzyme so it doesn’t work like it should. FMO3 stands for flavin-containing monooxygenase 3. This enzyme manages the impact that trimethylamine has on your body. Trimethylamine is a smelly chemical your body produces when you eat certain foods like fish, beans and eggs.

Normally, there’s a check-and-balance relationship between trimethylamine and FMO3: when your body produces trimethylamine, FMO3 enzymes break it down. That way, the chemical doesn’t smell bad when it moves from your digestive system into your bloodstream. When that doesn’t happen, trimethylamine builds up in your body, eventually seeping into your system so that your breath, sweat, saliva and pee smell like rotten fish.

People with primary trimethylaminuria develop the condition because they inherit abnormal FMO3 genes from both of their biological parents. In secondary TMAU, something keeps your FMO3 enzyme from breaking down trimethylamine. This can happen if:

• You have an illness, like liver failure or viral hepatitis, that keeps the enzyme from breaking down the trimethylamine.
• There’s an imbalance in your gut microbiome so there’s more trimethylamine in your system than the FMO3 enzymes can change into the non-smelly version of the chemical.
• You take choline or carnitine supplements. These nutrients play a role in producing trimethylamine.

What are complications of this condition?

Trimethylaminuria can damage your quality of life. Research shows people with the condition often avoid relationships, jobs and activities where others may notice the unpleasant smell that TMAU causes. People with this condition may develop mental health issues, including:

Rarely, people with TMAU have suicidal behavior, where they consider suicide.