Epistatic interactions between Chd7 and Fgf8 during cerebellar development: Implications for CHARGE syndrome.

CHARGE syndrome is a rare, autosomal dominant condition caused by mutations in the CHD7 gene. Although central nervous system defects have been reported, the detailed description and analysis of these anomalies in CHARGE syndrome patients lag far behind the description of other, more easily observed defects. We recently described cerebellar abnormalities in CHARGE syndrome patients and used mouse models to identify the underlying causes. Our studies identified altered expression of the homeobox genes Otx2 and Gbx2 in the developing neural tube of Chd7(-/-) embryos. Furthermore, we showed that the expression of Fgf8 is sensitive to Chd7 gene dosage and demonstrated an epistatic relationship between these genes during cerebellar vermis development. These findings provided, for the first time, an example of cerebellar vermis hypoplasia in a human syndrome that can be linked to deregulated FGF signaling. I discuss some of these observations and their implications for CHARGE syndrome.