The analysis of PSD-93 loss and gain of function in different brain regions has uncovered partly conflicting results that so far prevented a clear understanding of the physiological function of the paralogs PSD-93 and PSD-95 in the regulation of glutamatergic synapses, and what might go awry in neurodevelopmental disorders [19,23–25]. Here, DLG4 is linked to neurodevelopmental disorder.