During embryonic development, the different cell types that make our bodies activate distinct gene expression programs. But what happens when the mechanisms that regulate cell-specific gene expression fail and the cells start to express genes that should be silenced? This is a typical feature of cancer cells often associated with genomic instability. Our article proposes that these errors, referred to as illegitimate or spurious transcription, are also a hallmark of some neurodevelopmental disorders associated with intellectual disability.  We hypothesize that this form of dysregulation of gene expression in neurons may importantly contribute to the pathoetiology of these disorders. (By Dr. Angel Barco, https://jmg.bmj.com/content/early/2019/02/11/jmedgenet-2018-105668 )