Given the role of hevin in the establishment and maintainance of excitatory thalamocortical synapses (Risher et al., 2014; Singh et al., 2016), the increased density of thalamocortical synapses in cultures of Fmr1 KO astrocytes vs. WT astrocytes found here supports the importance of hevin during this developmental window and the development of aberrant connections in the FXS cortex. This evidence concerns the gene FMR1 and fragile X syndrome.