PCDH15 and Usher syndrome type 1: By further differentiating SMS NPCs into a relatively homogenous population of 2D cortical excitatory neurons, we found that SMS cortical neurons showed overexpression of SCZ-associated PCDHA3 and PCDHA5,89,90 neurodevelopmental disorder-associated PCDHGA5,91 and underexpression of PCDH15, which is associated with Usher syndrome type I (MIM: 602083)92 and bipolar affective disorder.93