All SMARCA4 germline alterations that have been reported until now in CSS patients are non‐truncating (either missense or small in‐frame deletions) clustered within the highly conserved ATPase/helicase domain, thus suggesting dominant‐negative or gain‐of‐function effects 1, 2, 3, 4, 5, 6. This evidence concerns the gene SMARCA4 and Coffin-Siris syndrome.