Deletion of the entire Rncr3 locus in mouse manifests as postnatal microcephaly and neurological phenotypes35, whereas our data show that null mutation of Rncr3 exons 2/3 is lethal before E8.5, and haploinsufficiency causes severe phenotypes during embryogenesis including microcephaly, loss of NEPCs/NPCs and premature neuronal differentiation. The gene discussed is MIR124-1HG; the disease is microcephaly.