The smallest region of deletion overlap affects only two coding genes, RALGPS1 and GARNL3 and is localized in close proximity to the known ID / epilepsy gene STXBP1. The seizure, ID, and DD phenotype in the deletions described here is at least partly independent from STXBP1, as shown by microdeletion sizes and expression studies. Here, RALGPS1 is linked to dentin dysplasia.