For some people with troublesome, unexplained body odor, an uncommon genetic disorder once known as "fish-odor syndrome" may be to blame, a new study finds.
The condition, known clinically as trimethylaminuria, is caused by emitting excessive amounts of the compound trimethylamine (TMA). TMA is produced when we digest foods rich in a substance called choline -- including saltwater fish, eggs, liver and certain legumes, like soy and kidney beans.
Trimethylaminuria is caused by defects in a gene known as FMO3. Those flaws hinder the body's ability to metabolize TMA and turn it into odor-free compounds.
TMA itself has a strong fishy smell, but only about 10 to 15 percent of people with trimethylaminuria have that specific malodor. And that may make it tougher for affected individuals to get a diagnosis.
No one is sure how prevalent trimethylaminuria is, though it is uncommon, according to Paul M. Wise, a researcher at the Monell Chemical Senses Center in Philadelphia.
For someone to have the disorder, he or she must inherit a defective copy of the FMO3 gene from both parents (who themselves would be unaffected "carriers"). Of course, if either of your parents has the disorder -- i.e. two copies of the affected gene -- they would also pass it on.
Studies in the UK have estimated that up to 1 percent of white people carry a flawed copy of FMO3, with some ethnic groups, including people from Ecuador and New Guinea having a higher rate.
But that doesn't tell you how many people have actual trimethylaminuria, Wise noted.
For the current study, Wise and his colleagues looked at how often trimethylaminuria was diagnosed in patients who came to Monell seeking help for unexplained, persistent body odor.
They found that about one-third of the 353 patients tested positive for trimethylaminuria. Testing involves measuring the level of TMA in the urine after a person drinks a beverage with added choline.
Of the 118 patients who tested positive, just 3.5 percent had complained of a "fishy" odor. Far more often, they reported general body odor, bad breath and a bad taste in the mouth.
Many of the patients in the study had seen several doctors and dentists (since bad breath is a common symptom) before being referred to Monell for testing. Some contacted the center on their own.
"That," Wise told Reuters Health, "is the major limitation of the study."
These were all people who had the motivation and the resources to dig for a diagnosis, Wise explained.
So it's unlikely that they are actually representative of all people with unexplained body odor problems, he said. And that means the researchers cannot conclude that one-third of all such individuals have trimethylaminuria.
George Preti, a Monell researcher who also worked on the study, said that in their experience, the second-most common culprit in unexplained body odor is chronic halitosis -- better known as bad breath.
"It can be mistakenly perceived as body odor," Preti explained, "because the odor is projected around your body when you speak or exhale."
Only a few labs in the U.S. perform testing for trimethylaminuria -- though your doctor can send samples to them, or you may be able to contact the center directly and receive a test kit.
The test typically costs a few hundred dollars, and insurance may not cover it or be accepted.
A less high-tech way to gauge on your own whether you might have trimethylaminuria would be to make diet changes. There is no cure for the disorder, but, Wise pointed out, the major way to manage it long-term is to avoid choline-rich foods.
If cutting out those foods improves your odor problem, that's a strong clue as to the underlying cause, he said.