ARID1B and Wiedemann-Steiner syndrome: All patients had a confirmed molecular diagnosis: mutations in the KMT2A gene were found in all WDSTS patients (Tables 1 and 1S); among KLEFS1, four patients had a chromosomal microdeletion partially or fully involving the EHMT1 gene (80%), while one had a point mutation in EHMT1 (20%) (Tables 1 and 1S ); all patients with CSS1 had mutations in ARID1B (Tables 1 and 1S ).