Mutations in the "FMO3" gene, which is found on the long arm of chromosome 1, cause trimethylaminuria. The "FMO3" gene makes an enzyme that breaks down nitrogen-containing compounds from the diet, including trimethylamine. These compounds are produced by bacteria in the intestine as they digest proteins from eggs, meat, soy, and other foods. Normally, the "FMO3" enzyme converts fishy-smelling trimethylamine into trimethylamine "N"-oxide which has no odor. If the enzyme is missing or its activity is reduced because of a mutation in the "FMO3" gene, trimethylamine is not broken down and instead builds up in the body. As the compound is released in a person's sweat, urine, and breath, it causes the strong odor characteristic of trimethylaminuria. Researchers believe that stress and diet also play a role in triggering symptoms.