FMR1 and fragile X syndrome: This means that, in human FXS embryos, early neurodevelopmental events such as the formation of the neural tube take place in the presence of FMRP; while FMRP absence probably affects late developmental stages, such as rapid neurogenesis from progenitors, migration and synaptogenesis, during the late phases of cortical and neo-cortical development (i.e., second and third trimesters).