While microdeletion and mutation of NSD1 causes Sotos syndrome, duplications of this region, and specifically of NSD1, have been identified in individuals presenting with growth retardation, developmental delay, microcephaly, and CHDs such as ASD and aortic stenosis.10,31–33 In the patient with duplication of the longer region, it is not possible to ascribe the phenotype specifically to NSD1 or FLT4. Our study thus identified CNVs in known regions likely to cause disease in five probands by American College of Medical Genetics and Genomics criteria. Here, FLT4 is linked to Global developmental delay.