Some good background reading on the TMAO/FMO3/FXR story. FMO3 catalyzes the conversion of TMA to TMAO, FMO3 levels are significantly correlated with TMAO levels, and TMAO levels explains 11% of the variation in atherosclerosis among common inbred strains of mice.
Trimethylamine-N-oxide, a metabolite associated with atherosclerosis, exhibits complex genetic and dietary regulation
https://www.ncbi.nlm.nih.gov/pubmed/23312283