Three forms of the enzyme, FMO1 found in fetal liver, FMO2 found in adult liver, and FMO3 are encoded by genes clustered in the 1q23-q25 region.
Tri forme ovog enzima, FMO1 u fetalnoj jetri, FMO2 u jetri odraslih osoba, i FMO3 su kodirani genima koji su grupisani u 1q23-q25 regionu.