PPP2R5D and Neurodevelopmental delay: Whether PPP2R5D-related NDD results from PPP2R5D gain of function or LoF is unclear, and we found that neuronal overgrowth phenotypes are not observed in neural progenitors and neurons lacking PPP2R5D. Furthermore, we have developed ASOs that selectively and efficiently reduce the E198K pathogenic transcript and rescue neurite outgrowth defects observed in patient iPSC-derived neurons.