Secondary Trimethylaminuria explained

Keywords/concepts:
Primary Trimethylaminuria urine test (TMAU1)
Secondary Triethylaminuria urine test (TMAU2)
Trimethylamine-N-Oxide
Trimethylamine
Overgrowth of bacteria that produce trimethylamine
DNA test looks for known FMO3 mutants/polymorphisms. FMO3 DNA test.

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Primary Trimethylaminuria urine test with Gas Chromatography/Mass Spectrometry : This is a test of trimethylamine-n-oxide and trimethylamine levels after a (presumed) trimethylamine load of some sort (either choline or foods containing choline, relying on the gut bacteria to turn it into trimethylamine). FMO3 enzyme turns trimethylamine into non-odorous trimethylamine-n-oxide. In a normal person, about 91% or more of the TMA is expected to be oxidized to TMA-Oxide by FMO3 in the liver. There is no internationally agreed level at which abnormal levels are categorized, but as a guideline, one expert suggests :

TMAO x 100/TMA + TMAO = more than 90%
TMAO x 100/TMA + TMAO = 70% - 90% : implies 'mild' TMAU
TMAO x 100/TMA + TMAO = less than 70% : suggests 'severe' TMAU

Secondary Trimethylaminuria urine test with Gas Chromatography/Mass Spectrometry : It seems secondary TMAU (TMAU2) is supposed to be all forms of increased TMA levels not to do with a genetic FMO3 deficiency, but in practice seems to be used to  label people with excessive TMA and TMAO levels who are also converting over 90% of the TMA to TMA-oxide. It usually implies they have an overgrowth of TMA-producing bacteria. If over 90 % conversion is reached, they seem to have a normal functioning FMO3 enzyme, but are producing so much TMA that the TMA and TMAO levels are very high and there is still enough TMA unconverted to produce a smell. This is to do with TMA concentration. Most labs do not seem to take TMAU2 into consideration in their results, with Sheffield Children's Hospital being an exception. Their current acceptable level of TMA is set at under 10.8. People can have both TMAU1 and TMAU2 (i.e. genetic TMAU and TMA overgrowth). Someone with only TMAU2 due to bacterial overgrowth should in theory be totally curable (by eradicating the bacteria overgrowth)  

Example of TMAU2 result :
TMA 20
TMAO 380
% conversion :  95% (normal)
TMA is over 10.8 (Sheffield level) so TMA smell still expected

Someone with only Secondary Trimethylaminuria would likely be advised not to do the DNA test, but at this point in understanding the problem a suggestion is to do the DNA test if possible if in doubt.

More information on TMAU testing