Trimethylaminuria (TMAU), sometimes known as “Fish-Odor Syndrome,” is a genetically transmitted metabolic disorder. The main symptom of TMAU is a foul-smelling body odor. The odor can smell like fish in some patients and like garbage in others.
Some people with TMAU have a strong odor all the time. However, others can have a more moderate smell that is not always present, which can make TMAU hard to diagnose.
People with TMAU are unable to completely break down trimethylamine (TMA), a chemical found naturally in many foods, especially those containing the essential nutrient choline.
As a result, their bodies build up high levels of trimethylamine. The foul-smelling trimethylamine is then excreted in urine, sweat, saliva, and breath.
An enzyme called flavin-containing monooxygenase enzyme 3 (FMO3) normally metabolizes – breaks down — dietary trimethylamine into a non-odorous byproduct. People with TMAU are born with a defective version of the gene that codes for FMO3 and the resulting faulty FMO3 enzyme is unable to completely break down trimethylamine.
Depending on the type of mutation in the FMO3 gene, the amount of unmetabolized trimethylamine (and related odor) varies from person to person. Only about 10 to 15 percent of patients with TMAU have an odor that can be characterized as “fishy.”
TMAU is diagnosed using a biochemical laboratory test that measures the amount of trimethylamine in a patient’s urine after they drink juice containing added choline.
All TMAU testing is handled directly through the Biochemical Genetics Laboratory at Children’s Hospital Colorado in Aurora, CO.
For information about TMAU testing, please contact Lab Client Services at Children’s Hospital Colorado at firstname.lastname@example.org (preferred) or at 720-777-6711.
Please note that the lab will need to work directly with your primary care provider (PCP) to arrange for the test. You should use the resources on this page to help you discuss TMAU with your PCP.
Because of the biochemical nature of the excessive production of TMA, TMAU is linked to the intake of choline-rich foods, including eggs; broccoli; certain legumes such as soy, kidney beans; wheat germ; saltwater fish; and organ meats, including liver.
Currently there is no cure for TMAU, but treatment options, including avoidance of choline-containing foods, may help reduce odor production. However, choline is an essential nutrient that is needed by your body for many functions. This means that restricting your choline intake without having definitive biochemical TMAU testing and diagnosis could be detrimental to your health. Always consult your physician before trying to restrict dietary choline.
Experts who have tackled the choline question to better understand TMAU recommend consulting a registered dietitian and/or a licensed nutritionist before making major changes in your diet. In 2008, a group of nutrition scientists published a US Department of Agriculture Report called the Database for the Choline Content of Common Foods, inspired by a 1999 conference on TMAU and sponsored by the National Institutes of Health. It contains a table of hundreds of everyday foods and the amount of choline in each, which could be used in supervised meal planning.
A 2004 article by some of the same scientists on the 2008 USDA report includes a table of choline-rich foods. However, individuals should work with a registered dietitian to create a plan that is tailored to their food preferences, culture, and other factors to make sure they are meeting all their individual requirements for vitamins and minerals.