SRRM4 and autism spectrum disorder: In particular, this microexon, which functions in transcriptional activation, is highly conserved in vertebrates, regulated by changes in neuronal activity, frequently partially skipped in individuals with autism spectrum disorder (ASD), and controlled by trans-acting regulators that have genetic and functional links to ASD, including the ‘master activator’ of microexons, the Ser/Arg-repeat matrix protein 4 (SRRM4; also known as nSR100), and the neural enriched splicing regulator RBFOX123,25–27.