Fish Odor Syndrome (Trimethylaminuria)

What is Fish Odor Syndrome?

Fish odor syndrome is also known as Trimethylaminuria and fish malodor syndrome and is a rare metabolic disorder that causes a flaw in the normal production of an enzyme known as flavin-containing monooxygenase 3 (FMO3).

When FMO3 isn’t working properly or not enough of the enzyme is being produced the body cannot properly convert Trimethylamine from compounds in food digestion into Trimethylamine oxide via a process known as N-oxidation. The buildup of Trimethylamine is released from the body via urine, sweat, and breath and produces a pungent fishy body odor.

The condition is more common in women than men and can adversely affect a person’s career, relationships, and social life. Trimethylaminuria is inherited as an autosomal recessive genetic trait. A proper diagnosis can be made by measuring the ratio of Trimethylamine to Trimethylamine oxide.

What are the Symptoms of Fish Odor Syndrome?

Symptoms include stale fish syndrome and usually present with a strong fishy body odor. Most people affected with fish odor syndrome appear normal and healthy.

Fish Odor Syndrome Causes

Fish odor syndrome, or trimethylaminuria, is a genetic disease characterized by overpowering body odor and the scent of rotting fish. It is caused by excessive production of trimethylaminuria, or TMA, a component in sweat. The FMO3 gene is responsible for the production of TMA, and this condition occurs when the gene becomes corrupted. With a corrupted gene, the body is not able to properly break down certain nitrogen-containing compounds; as a result, the body excretes excessive TMA, causing a foul odor.

Fish odor syndrome is typically inherited in an autosomal recessive pattern, meaning that both parents are carriers of a corrupted FMO3 gene. When both copies of the corrupted FMO3 gene are passed on to a child, that child may develop fish odor syndrome. Many carriers may experience temporary or mild fish odor syndrome, although they may be unaware that they are a carrier of the gene unless it becomes present in their child.

How is Fish Odor Syndrome Treated?

In mild cases symptoms go away when foods containing lecithin or choline are removed from the diet. In severe cases a gut-sterilizing antibiotic such as Metronidazole may be given. The use of body lotions and slightly acidic soaps can convert Trimethylamine on the skin into a form that can be removed by washing.

Dietary supplements such as copper chlorophyllin and activated charcoal can bind Trimethylamine in the gut and reduce the amount available for absorption.

Fish Odor Syndrome Prevention

Symptoms are often present from birth. Fish odor syndrome can also occur temporarily in premature babies and in healthy menstruating people at the beginning of their period.

Despite the fact that fish odor syndrome is not preventable, it is treatable. Treatments often include dietary restrictions; frequent foods eliminated include marine fish, Brussels sprouts, chicken and beef liver, eggs, mustard seeds, and raw soybeans, as these foods stimulate the production of TMA. Additionally, certain acidic lotions can remove excessive TMA from the skin. Activated charcoal, copper chlorophyllin, antibiotics, laxatives, and riboflavin supplements are all additional ways of treating some part of fish odor syndrome. Another simple method of moderating the effect of the disease involves washing clothes frequently to remove excess TMA from the fabric.

While no one method seems to be entirely effective, people who suffer from fish odor syndrome may be able to mitigate its effects by using a combination of treatments.

Last Reviewed:
October 06, 2016
Last Updated:
December 22, 2017
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