We suggest that a more dramatic obliteration of U2AF2–RNAinteractions would be lethal rather than lead to NDD, since U2AF2recognizes the majority of splice sites.8−10 An intriguing analogycan be made with de novo mutations of MeCP2, whichoccur almost exclusively in Rett syndrome,18 leading to progressive loss of motor skills and speech. The gene discussed is MECP2; the disease is Neurodevelopmental delay.