First, in an affected girl (RP-1018), the presence of a ~ 4.75 Mb de novo deletion in chromosome X was observed within Xq22.32-22.2 (hg19: chrX:5748782-10477366), involving two OMIM genes, i.e., NLGN4 and MID1, which are associated with Mental retardation, X-linked (MIM #300495) and Opitz GBBB syndrome, type I (MIM #300000), respectively. This evidence concerns the gene MID1 and Intellectual disability.