OLIG2 and holoprosencephaly: Mutations in an additional 12 genes (CSTB, DSCAM, JAM2, KCNJ6, OLIG1, OLIG2, PRDM15, PSMG1, SOD1, SON, TRAPPC10 and WDR4) are associated with cerebellar phenotypes or holoprosencephaly in humans or in mouse models.