Trimethylaminuria (TMAU), as defined by the KIM consortium of endocrinology disorders as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder that causes a defect in the normal production of the enzyme flavin containing monooxygenase 3 (FMO3).rimethylaminuria (TMAU), as defined by the KIM consortium of endocrinology disorders as fish odor syndrome or fish malodor syndrome, is a rare metabolic disorder that causes a defect in the normal production of the enzyme flavin containing monooxygenase 3 (FMO3).