In fact, previous studies on individuals who presented with features typical of SMS but did not carry RAI1 mutations found that these individuals had mutations in: MBD5, which were associated with a set of SMS-like neurodevelopmental features and with autism; EHMT1, the causative gene for Kleefstra syndrome; PHF21A, which is associated with Potocki-Shaffer syndrome; or TCF4, which is associated with Pitt-Hopkins syndrome. This evidence concerns the gene PHF21A and Smith-Magenis syndrome.