We previously reported mutations in NSD1, EZH2, DNMT3A (MIM: 602769), and PPP2R5D (MIM: 601646) in 198 case subjects. The relevant references are in Table S1. Intragenic mutations in these genes were detected with Sanger sequencing. NSD1 is unusual among the 14 OGID genes included in this study in being prone to deletion by a 2 Mb 5q35 microdeletion, mediated by flanking low-copy repeats.16 We used MLPA to identify 5q35 microdeletions encompassing NSD1.17 NSD1 MLPA is also capable of detecting exon CNVs that account for ∼5% of NSD1 mutations.17 Microdeletions and exon CNVs in the other genes were not sought, but are unlikely to be a major contributor because the surrounding sequence architecture and/or mechanism of pathogenicity make it much less likely that such events will cause OGID.