Holoprosencephaly with cerebellar vermis hypoplasia in 13q deletion syndrome: Critical region for cerebellar dysgenesis within 13q32.2q34.

We describe two unrelated patients with terminal deletions in the long arm of chromosome 13 showing brain malformation consisting of holoprosencephaly and cerebellar vermis hypoplasia. Array comparative genomic hybridization analysis revealed a pure terminal deletion of 13q31.3q34 in one patient and a mosaic ring chromosome with 13q32.2q34 deletion in the other. Mutations in ZIC2, located within region 13q32, cause holoprosencephaly, whereas the 13q32.2q32.3 region is associated with cerebellar vermis hypoplasia (Dandy-Walker syndrome). The rare concurrence of these major brain malformations in our patients provides further evidence that 13q32.2q32.3 deletion, harboring ZIC2 and ZIC5, leads to cerebellar dysgenesis.