Moreover, the release of insulin-like growth factor-binding protein 2 (Igfbp2), an inhibitor of insulin-like growth factor secretion, has been shown to reverse neurite growth inhibition by blocking bone morphogenetic protein (BMP) signaling in astrocytes associated with fragile X syndrome and RTT (Zehnder et al., 2021). Here, IGFBP2 is linked to Rett syndrome.