The inheritance pattern of SMS is autosomal dominant, but most cases are sporadic, although parental mosaicism and rare heritable chromosome rearrangements that lead to this complex contiguous gene syndrome is associated with an interstitial microdeletion at the 17p11.2 chromosome region that includes the retinoic acid-induced 1 (RAI1) gene (around 90% of cases) or by RAI1 gene point mutation (10% of cases of SMS).6–8. This evidence concerns the gene RAI1 and Smith-Magenis syndrome.