PPIB and lissencephaly spectrum disorders: Consistently with this hypothesis, suppression of the early activation of Wnt/β-catenin signaling by electroporating Wnt inhibitor Dkk1 into the cerebral cortex, reduced the number of cortical APs, bRG and IPs and restored lissencephaly in Lmx1a−/−;b−/− mice, revealing a critical role of Wnt signaling in the development of cortical gyrification in this mutant (Fig. 4).