ARF1 and periventricular nodular heterotopia: Activating mutations affecting ARF1 result in a complex neurodevelopmental condition called “periventricular nodular heterotopia.” This neuronal migration disorder is characterized by microcephaly with brain malformations and progressive cerebral atrophy and spasticity (Ge et al., 2016), and invertebrate and vertebrate embryo models expressing dominant ARF1 exist, which show typical non-canonical Wnt-dependent PCP defects (Carvajal-Gonzalez et al., 2015).