CSS was first described in 19701 and in 2004 three unrelated Finnish patients were reported.2 Approximately 7% to 12% of CSS patients have pathogenic SMARCB1 variants and 7% have pathogenic ARID1A variants.3,4 CSS classifies further into twelve subgroups defined by the genetic etiology. This evidence concerns the gene ARID1A and Coffin-Siris syndrome.