Case Study 3: Trimethylamine and Fish Odor Syndrome

We humans naturally avert the smell of decay. If the smell of rotting fish (or for that matter, even raw fish) turns you off, imagine someone have an illness with a “fishy” smell as one of its symptoms.

Here is another case from Richard Ludueña’s Learning More Biochemistry: 100 New Case-Oriented Problems (1997):

Your patient exudes a strong smell of rotting fish. This is evident in his breath and sweat. This causes a great deal of stress for him; he has had to change jobs several jobs several times because of complaints from co-workers. He has elevated levels of trimethylamine in his urine. You are successfully treating him with metronidazole.

The compound trimethylamine, with the formula N(CH3)3, is known for its foul smell that resembles rotting fish and bad breath. From the case, it could be seen that trimethylamine could be the compound causing the awful smell. The smell is propagated by its volatility, and by outlets in which it could be released from the body (urine, sweat, breath, and reproductive fluids).

The disorder in question is the aptly named Fish Odor Syndrome, or trimethylaminuria. The defect lies in the failure for trimethylamine to be metabolized properly and completely, causing a buildup of this odorous compound.  There might be mutations in the enzyme trimethylamine oxidase, which converts trimethylamine into trimethylamine-N-oxide, which is non-volatile and thus not smell. The reaction attaches an oxygen to the amine. The more specific name of the enzyme is flavin-containing monooxygenase 3 (FMO3). More technical information on the enzyme and its relation with trimethyaminuria here and here.

Trimethylamine has the smell of rotting fish.

Trimethylamine-N-oxide is non-odorous. It is a derivative of trimethylamine by the work of the enzyme trimethylamine oxidase.

A common diagnostic procedure for trimethylaminuria is urine test. As indicated in this case study, there might be higher than normal levels of trimethylamine in the patient’s urine.

Trimethylamine is not commonly found in food. However, bacteria in the intestine metabolize choline to trimethylamine. Choline-rich food trigger the production of trimethylamine and might worsen the effects of the condition. Thus, choline-rich food should be avoided.  Examples include egg yolk, kidney, legumes, soy beans and legumes. These bacteria also do the reverse of the trimethylamine oxidase reaction, thereby producing trimethylamine. Thus, foods rich in trimethylamine-N-oxide, such as saltwater fish, should not be taken. In other words, choline and trimethylamine-N-oxide, by bacterial work, transform into trimethylamine. A study have shown that an aerobic bacterium named Streptococcus sanguis I is able to get trimethylamine from choline (abstract here).

Simple pathway connecting choline, trimethylamine and trimethylamine-N-oxide

Nevertheless, trimethylaminuria is inherited (but rare). Like in Case Study 1 (Blue Diaper Syndrome), Fish Odor Syndrome is acquired in an autosomal recessive fashion. As with the previous case, we will skip a discussion on the genetics of such diseases. According to a 2003 BBC News article, there have been only 200 cases worldwide since the discovery of the disorder in the 70s.

The case mentions Metronidazole. The antiobiotic (Metronidazole being antibacterial and antiprotozoal) acts against Bacteroides and Clostridium, bacteria which release the odorous trimethylamine.  Thus, antiobiotic treatment might alleviate the condition. However, this is just one of the possible cures for Fish Odor Syndrome. Many more are proposed, aside from dietary restrictions and antiobiotics, as indicated by the National Human Genome Research Institute (link is provided below).

Metronidazole could be a treatment for fish odor syndrome.

Main References

1. Ludueña, R. F. Learning More Biochemistry: 100 New Case-Oriented Problems, Problem 6, Wiley-Liss, Inc. (1997)

2. Trimethylaminuria

• Wikipedia
• National Genome Research Institute

3. Trimethylamine in Wikipedia: http://en.wikipedia.org/wiki/Trimethylamine

Image Sources

https://scientiaetarte151.files.wordpress.com/2012/10/rotten2bfish.jpg?w=200

http://jeb.biologists.org/content/205/3/297/F1.large.jpg

[post by Ajep Perez]