Trimethylaminuria (TMAU), also known as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder that causes a defect in the normal production of an enzyme named flavin-containing monooxygenase 3 (FMO3). When FMO3 is not working correctly or if not enough enzyme is produced, the body loses the ability to properly convert trimethylamine (TMA) from precursor compounds in food digestion into trimethylamine oxide (TMAO), through a process called N-oxidation. Trimethylamine then builds up and is released in the person's sweat, urine, and breath, giving off a fishy odor. Primary trimethylaminuria is caused by genetic mutations that affect the FMO3 function of the liver. Symptoms matching TMAU can also occur when there is no genetic cause, yet excessive TMA excreted - this has been described as secondary trimethylaminuria (TMAU2). TMAU2 can be caused simply by a precursor overload (ingesting too many dietary TMA precursors), hormonal issues related to menstrual cycles, liver damage, or liver and kidney failure. As a symptom rather than a disease, TMAU2 is temporary and will resolve as the underlying cause is remedied (in the instance of menstrual related TMAU2, at menopause). From Wikipedia
