after 5 experts, 3 in the uk and 2 in the US, this is the closest I can can get;
""Thank you for your mail and my regards to Dr. Mitchell. Unfortunately we don't have any statistics to answer the question you pose. As you know trimethylaminuria (TMAU) is an odor-producing disorder that may be caused by a spectrum of changes within the Flavin-containing monooxygenase 3 (FMO3) gene. Some of the more common (found in up to 10% or more of the population) polymorphic changes in the gene are also reported to cause diminutions in the ability to oxidize trimethylamine (TMA), particularly when two of them exist in the same individual. Consequently while I don't know an exact number one could use the definition of a "rare disease" and say up to 1 in 200,000 may have the disorder. However, I think this refers to severe cases caused by rare mutations in FMO3. To further confuse the situation, we have a manuscript about to appear which used an exome analysis of 10 TMAU-positive individuals which shows the involvement of other genes, in addition to FMO3, in TMAU.""
George Preti, Ph.D.
Member, Monell Chemical Senses Center
3500 Market Street
Philadelphia, PA 19104