What is Trimethylaminuria?

Trimethylaminuria (TMAU) is a rare genetic condition that causes a distinctive fish-like body odor. The odor is described as smelling like rotting fish or rotting eggs. Trimethylaminuria can cause social and/or psychological problems because of the body odor. The odor sometimes can be more severe during puberty, with excessive sweating, and, in females, near the time of menstruation, oral contraceptive use, or menopause.

The odor associated with trimethylaminuria happens because unusually high levels of trimethylamine (TMA), which has a strong odor, are released in the urine, breath, and sweat. This is caused by mutations (changes or mistakes) in the gene FMO3. FMO3 normally tells the body to make an enzyme that metabolizes (breaks down) TMA into an odorless molecule. When the body cannot break down TMA, the body gets rid of it in urine, sweat, and other fluids.

Trimethylaminuria is diagnosed by measuring the amount of TMA present in the urine and/or by genetic testing of the FMO3 gene.

Trimethylaminuria is treated with a change in diet. Avoiding foods with high levels of TMA (or other compounds which are broken down into TMA by the body) will improve the body odor. Using acid soaps and body lotions, taking dietary supplements such as charcoal or copper-chlorophyllin tablets, intermittent antibiotics, and riboflavin supplements may also help to decrease the body odor.

The way trimethylaminuria is inherited is called "autosomal recessive." This means that to be affected, a person must have a mistake (mutation) in both copies of the FMO3 gene in each cell. The parents of a child with trimethylaminuria usually each carry one copy of the gene with a mutation. The parents are referred to as carriers. Carriers typically do not show signs or symptoms of the condition. When two carriers of an autosomal recessive condition have children, each child has a 25% (1 in 4) chance to have the condition, a 50% (1 in 2) chance to be a carrier like each of the parents, and a 25% chance to not have the condition and not be a carrier. Learn more about autosomal recessive inheritance from the Centre for Genetics Education.

Diagnosis of trimethylaminuria (TMAU). Sheffield Children's.

Phillips, I. & Shephard, E. (2015). Primary Trimethylaminuria.In: Pagon RA, Adam MP, Ardinger HH, et al., editors. GeneReviews® [Internet]. Seattle (WA): University of Washington, Seattle; 1993-2016.

Trimethylaminuria. (2013). Genetics Home Reference.

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