APP and autism: Additionally, levels of several targets of FMRP including ras-related C3 botulinum toxin substrate 1 (RAC1), homer 1, striatal-enriched protein tyrosine phosphatase (STEP), and amyloid beta A4 precursor protein (APP) are also altered significantly in subjects with autism [7] pointing to involvement of mGluR5-FMRP signaling abnormalities in autism.