Dp10Yey mice were generated to carry an internal duplication spanning the 39 Hsa21 protein-coding orthologs mapping to Mmu10, and several of these genes—such as ADAR2, S100B, CSTB, PRMT2, and TRPM2—have been shown to play a role in brain development and function, such that aberrant gene dosage may be related to intellectual disability in DS (Block et al., 2015, Gupta et al., 2016). The gene discussed is S100B; the disease is Dravet syndrome.