FMO3 gene: MedlinePlus Genetics (2024)

FAQs

What is the function of the FMO3 gene? ›

Normal Function

The FMO3 gene provides instructions for making an enzyme that is part of a larger enzyme family called flavin-containing dimethylaniline monooxygenases (FMOs). These enzymes break down compounds that contain nitrogen, sulfur, or phosphorus.

Riboflavin, or vitamin B2, may help increase any existing FMO3 enzyme activity in the body. People can take the recommended dosage of 30–40 mg between three and five times a day with meals. People can also avoid using alkaline soaps and body lotions with a high pH level.

FMO3 stands for flavin-containing monooxygenase 3. This enzyme manages the impact that trimethylamine has on your body. Trimethylamine is a smelly chemical your body produces when you eat certain foods like fish, beans and eggs.

Genetic deficiencies of the FMO3 enzyme cause primary trimethylaminuria, also known as "fish odor syndrome". FMO3 is also involved in the metabolism of many xenobiotics (i.e., exogenous compounds which are not normally present in the body), such as the oxidative deamination of amphetamine.

Trimethylaminuria, or fish odor syndrome (FOS), is a condition characterized by the presence of trimethylamine (TMA)—a tertiary amine whose odor is described as resembling that of rotting fish—in the urine, sweat, and expired air.

The primary genetic form of trimethylaminuria (TMAU) is caused by inherited defects in the flavin-containing monooxygenase 3 (FMO3) gene. Defective FMO3 has a decreased ability to catalyze the N-oxygenation of the dietary-derived malodourous amine, trimethylamine.

Things that can make it worse include: sweating. stress. certain foods – such as fish, eggs and beans.

People with TMAU can receive an appropriate dietary treatment by excluding TMA precursors. Alternatively, dietary supplementation with riboflavin (vitamin B2, a cofactor required for the activity of acyl-CoA dehydrogenases [40]) reduces TMA excretion and body odor in some patients with TMAU [29].

B2 vitamin treatment dramatically improved the unpleasant body odor and the ratio of TMA/Cr vs TMAO/Cr in the urine in the children. Other patients presented a particular psychological or psychiatric phenotype.

When citric acid reacts with Trimethylamine, a weak base, they undergo a neutralization reaction, forming a salt that does not have the fishy odor. This reaction helps to neutralize the smell by breaking down the basic compound that causes the odor, effectively masking the fishiness.

How rare is TMAU? ›

Trimethylaminuria is a rare metabolic disorder. Several hundred cases have been reported in the medical literature. Some clinicians believe that the disorder is under-diagnosed since many people with mild symptoms do not seek help.

How does an acid like lemon juice remove the fishy odor? Citric acid neutralizes the amines in fish by converting them into healthy salts that will not be airborne like the amines.

FMO3 converts the odorous TMA to nonodorous TMA N-oxide (TMAO), which is excreted in urine. Impaired FMO3 activity gives rise to the inherited disorder primary trimethylaminuria (TMAU). Affected individuals cannot produce TMAO and, consequently, excrete large amounts of TMA.

The symptoms of trimethylaminuria can be improved by changes in the diet to avoid precursors, in particular TMAO which is found in high concentrations in marine fish. Treatment with antibiotics to control bacteria in the gut, or activated charcoal to sequester TMA, may also be beneficial.

As excess trimethylamine is released in a person's sweat, urine, and breath, it causes the odor characteristic of trimethylaminuria. Researchers believe that stress and diet also play a role in triggering symptoms.

TMAO shows an important role in cholesterol metabolism and metabolic stress under cholesterol overload. Intracellular cholesterol is stored with endoplasmic reticulum (ER). Disruption of cholesterol homeostasis influences the functioning of ER, which is leading to ER stress.

Trimethylamine is a colorless gas or liquid below 37oF (3oC), with a strong fishy odor. It is used as a warning (smell) agent in natural gas, as an insect attractant, and in chemical manufacturing.

Primary trimethylaminuria is a rare metabolic disorder caused by changes (variants) in the FMO3 gene. Humans have several FMO genes, but only variants in FMO3 cause trimethylaminuria. For reasons that are unclear, many different variants of the FMO3 gene exist.

The FMO3 enzyme normally converts fishy-smelling trimethylamine into another compound, trimethylamine-N-oxide, which has no odor. Trimethylamine-N-oxide is then excreted from the body in urine. Researchers believe that the FMO3 enzyme also plays a role in processing some types of drugs.