DLL1 and cerebral cortical dysplasia: The third distally located HI-gene of interest for the common 6q terminal deletion phenotype is DLL1. Recently, Fischer-Zirnsak et al. [29] described 14 patients with pathogenic heterozygous variants of DLL1 and one patient with a deletion including DLL1. These patients presented with hypotonia, scoliosis and a neurodevelopmental phenotype including variable brain abnormalities (ventriculomegaly/hydrocephaly, corpus callosum abnormality and cortical dysplasia), seizures and autism spectrum disorder.