What is the cause?

The bacteria in our bowel help us to digest foods such as eggs, beans and seafood. In the process, they produce a strong-smelling chemical called trimethylamine.

Normally, an enzyme (protein) called flavin-containing monooxygenase 3 (FMO3) is produced by the liver toturn trimethylamine into the odourlessmolecule trimethylamine N-oxide.Most people havean FMO3gene, which provides instructions for making this enzyme.

Faulty gene

In most people with trimethylaminuria, the FMO3 enzyme is missing or their FMO3 gene doesn't work as well as other people's.This allows trimethylamine to build up in the body.

Usually,those with trimethylaminuria haveinherited the faulty FMO3 gene from both their parents. In other words, each parent will carry one copy of the faulty gene and be a "carrier" of the condition.

Carrier parents may not have symptoms themselves, or may only have mild or temporary episodes of body odour.

It's estimated that 1% of the UK population are carriers of the faulty gene that causestrimethylaminuria.

Other causes

Noteveryone with trimethylaminuriahas the faulty FMO3 gene.Some cases may be caused by an excess of certain proteins in the diet, or an abnormal increase in the gut bacteria that produce trimethylamine.

A few cases oftrimethylaminuria have been linked with liver or kidney disease, where theFMO3 enzyme is underactive.

Women are more likely than men to have the condition possibly because female sex hormones such as progesterone and oestrogen aggravate the symptoms. Some cases appear to be worse around puberty and, in women, at the following times:

• just before or after periods
• after taking the contraceptive pill
• around the menopause

Temporary symptoms of this condition have also been identified in a small number of premature infants.

Stress and diet may also play a role in triggering the odour.