MYCBP2 (also called Phr1 in rodents) is an evolutionarily conserved regulator of axon development [31,32], and genetic variants in MYCBP2 were recently shown to cause a neurodevelopmental spectrum disorder called MYCBP2-related developmental delay with corpus callosum defects (MDCD) [33]. This evidence concerns the gene MYCBP2 and MYCBP2-related developmental delay with corpus callosum defects.