To investigate the function of ARID1B in craniofacial development, we obtained skin fibroblasts from two unrelated ARID1B+/− Coffin-Siris Syndrome patients (hereafter, Patient 19 and Patient 26; Fig. 1a, b), one male and one female, both carrying previously identified de novo ARID1B mutations. This evidence concerns the gene ARID1B and Coffin-Siris syndrome.