Given the normal routine blood workup and the presence of dysmorphic features, hypertrichosis, along with GDD, a whole-exome sequencing (WES) study was conducted (Table 2), which identified the pathogenic heterozygous novel variant c.1314del p.(Glu439Serfs*63) in the ARID1B gene, confirming a diagnosis of Coffin-Siris syndrome. This evidence concerns the gene ARID1B and Coffin-Siris syndrome.