The reduction in neurite length and dendritic arborization identified in FXS- hiDFP-derived neurons is consistent with phenotypes observed in both neonatal and adult FMR1 KO or knock-down mouse models of FXS (Castren et al., 2005; Shen et al., 2019; Yau et al., 2019; Lannom et al., 2021) and human FXS patient derived iPSCs (Sheridan et al., 2011; Doers et al., 2014; Achuta et al., 2018; Utami et al., 2020). Here, FMR1 is linked to fragile X syndrome.