Trimethylaminuria causes people to smell like rotten fish because their urine, sweat and breath contain elevated levels of a harsh chemical that is normally metabolized in the gut. (Image credit: AndreyPopov via Getty Images)
Disease name: Trimethylaminuria (TMAU), also known as “fish odor syndrome.”
Affected populations: TMAU is a rare metabolic disorder that causes a person to exude a rotten fish odor. The condition is more common in women than men, and there is evidence that hormones such as progesterone may worsen symptoms in patients.
The exact prevalence of TMAU is unknown, and estimates of the number of cases vary from 1 in a million to 1 in 200,000 people.
Causes: Patients with TMAU have a fishy odor due to a buildup of a chemical known as trimethylamine in the body. Trimethylamine is produced by bacteria in the gut as a byproduct of digesting certain foods, including eggs, liver, legumes, and some types of seafood such as fish, squid, and crab.
Normally, an enzyme in the body breaks down trimethylamine into a non-aromatic compound called trimethylamine N-oxide, which is then excreted in the urine. This enzyme is encoded by the FMO3 gene.
However, in patients with TMAU, this enzymatic process does not occur, so trimethylamine accumulates in the body and is eventually excreted in excess in urine, sweat, and breath, causing the rotten fish smell.
Most cases of TMAU are due to mutations in the FMO3 gene, which prevent the enzyme it codes from working properly. In these cases, patients inherit the disease in an autosomal recessive manner, meaning they must receive two copies of the mutated FMO3 gene — one from each parent — to develop the condition.
Less commonly, TMAU can be caused by overconsumption of foods that promote trimethylamine production. It can also be caused by liver failure and certain medical procedures, such as testosterone replacement therapy, which affect trimethylamine metabolism and production, respectively. Hormonal changes caused by the menstrual cycle can also trigger a temporary form of TMAU.
People with trimethylaminuria should avoid eating seafood, which may worsen their symptoms.
Symptoms: Signs of TMAU may be noticeable at birth or appear later in life, usually at the onset of puberty (around ages 8 to 13 in girls and 9 to 14 in boys), when
Sourse: www.livescience.com
