FMR1 and fragile X syndrome: To test whether the loss of one Cyfip1 allele and reduction in expression of the FMRP binding partner CYFIP1, which mimics microdeletion at locus 15q11.2 in humans, produces a similar reduction in GABAAR δ-subunit-dependent tonic inhibition as observed in FXS, we evoked currents using the δ-subunit-selective drug THIP (Gaboxadol).