RAI1 and Smith-Magenis syndrome: Whereas SMS is classically associated with a deletion within cytogenetic G-band 17p11.2 that includes the RAI1 gene (about 90 % of individuals) or a nucleotide variant in that gene (about 5 %) [1, 9–12], some reports suggested genetic heterogeneity as SMS-like individuals were found to recurrently harbor deletions of the 2q37.3 or 2q23.1 cytobands encompassing HDAC4 and MBD5, respectively [13–15].