Definition:

Trimethylaminuria (TMAU), also known as fish odour syndrome, is a metabolic disorder. TMAU usually presents with a body odour resembling that of rotten or decaying fish, the result of excess excretion of trimethylamine (TMA) in the breath, sweat, urine, and reproductive fluids. Primary TMAU is most often caused by a functional defect of flavin mono-oxygenase 3 (FMO3), and the genetic disorder is inherited in an autosomal recessive manner as a consequence of mutations in the FMO3 gene. Secondary TMAU has been described in patients with severe liver disease (which is the major site of activity of the FMO3 enzyme) and chronic renal disease (as a consequence of bacterial overgrowth in the gut), and in patients treated with large doses of betaine or possibly L-carnitine. In addition, transient TMAU has been reported in a preterm infant who was fed with choline-rich food supplements and has been reported in some women just at the onset of menstruation.