Among the most prominent and most studied BAFopathies are the clinically overlapping syndromes CSS and Nicolaides-Baraitser (NCBRS) (MIM: 601358), caused by variants in BAF complex proteins: ARID1B in CSS1, SMARCB1 in CSS2, and SMARCA4 in CSS4; and SMARCA2 in NCBRS. The gene discussed is ARID1B; the disease is BAFopathy.