To date, compelling evidence demonstrates that CSS is caused by heterozygous pathogenic variants in ARID1A, ARID1B, SMARCA2, SMARCA4, SMARCB1, SMARCE1, ARID2, DPF2, BICRA, PHF6, SMARCC2, SMARCD1, SOX11 and SOX4 [5–12]. Here, SMARCA4 is linked to Coffin-Siris syndrome.