Apart from KMT2C, mutations in additional components of the well-defined COMPASS protein complex, including the KMT2C paralog KMT2D, and the histone demethylase KDM6A, are causative for Kabuki syndrome, another ID disorder which shares autistic behavior and developmental delay with Kleefstra syndrome and the patients described here [8]. This evidence concerns the gene KMT2C and Global developmental delay.