Trimethylaminuria: Or Fish Malodor Syndrome

Trimethylaminuria, also known as Fish Malodor or Fish Odor Syndrome, is a rare genetic disorder. It's sufferers have an excess amount of the amino acid trimethylamine in their body. It's the same compound that makes rotting fish smell, well, fishy. There is a malfunction in the enzyme that breaks down the amino acid and excess quantities are secreted in sweat, urine and breath - with a strong fishy odour.

The intensity of the smell can very over time. Sometimes it can be very strong indeed and in other situations reasonably mild, though still noticeable.

Although sufferers are healthy in every other respect, the condition can greatly affect their social lives, leading some individuals to become isolated and depressed.

This rare genetic disorder is hereditary and passed along the generations in an autosomal recessive pattern. That means that a person has two bad copies of the gene in each cell. Each parent of the affected individual is a carrier and may well experience mild and temporary effects of Fish malodor syndrome.

Defects in the FMO3 gene on chromosome 1 are responsible for the condition. In normal circumstances the FMO3 gene codes for an enzyme that breaks down nitrogen containing compounds in our food, and this includes trimethylamine. The amino acid is produced by bacteria in the intestine when they digest proteins from food. The enzyme usually converts this into another compound that has no odour. Mutated FMO3 genes can lead to the enzyme not being made at all or they can result in reduced activity of the enzyme.

There may also be some non-genetic factors that can lead to Fish malodor syndrome and those can be an excess of some proteins in the diet or an increase in the number of bacteria that usually break down trimethylamine in the digestive system.

Currently there are no cures for the genetic mutations that cause this rare disorder and the treatment options are limited. Individuals with trimethylaminuria are advised to cut out certain foods from their diet including eggs, meat and some fish. They may also be given small doses of antibiotics to reduce the number of bacteria in the gut. Genetic counselling is also sometimes offered so people can understand the condition and to help them avoid episodes of depression.