FISH is considered the gold standard method for chromosome microdeletion syndromes diagnosis.4,6,38,39 The WBS diagnosis rate of FISH is over 90% of the cases.39 WBS molecular etiology was described in the 1990s, the same decade that FISH was implemented as a diagnostic tool for WBS individuals.40,41,42 In 1993, Ewart et al.1 found that the molecular cause of WBS was a microdeletion at chromosome 7q11.23 after observing a elastin gene (ELN) hemizygosity by FISH. This evidence concerns the gene ELN and Williams syndrome.