Because the Zic2 knockdown mouse is the first mutant with HPE and spina bifida to survive to the perinatal period, the mouse will promote analyses of not only the neurulation but also the pathogenesis of human HPE.
Furthermore, the studies confirm the extent of ZIC2 allelic heterogeneity and that pathogenic variants of ZIC2 are associated with both classic and middle interhemispheric variant (MIHV) HPE which arise from defective ventral and dorsal forebrain patterning, respectively.
Hemizygosity for ZIC2, which is located in the 13q32 critical deletion region, results in holoprosencephaly (HPE) in humans, and diminished expression of ZIC2 results in HPE as well as lumbosacral NTDs in mice.
In order to improve the molecular characterization of 13q monosomy, 12 new patients (9 foetuses and 3 children) were collected based on a cohort of holoprosencephaly (HPE) linked to ZIC2 gene deletion and/or patients with 13q deletion diagnosed by standard karyotype.
Molecular screening of SHH, ZIC2, SIX3, and TGIF genes in patients with features of holoprosencephaly spectrum: Mutation review and genotype-phenotype correlations.
Mutation of Zic2 causes HPE via a transient defect in the function of the organizer region at mid-gastrulation which causes an arrest in the development of the prechordal plate (PCP), a structure required for forebrain midline morphogenesis.
Mutations in ZIC2, located within region 13q32, cause holoprosencephaly, whereas the 13q32.2q32.3 region is associated with cerebellar vermis hypoplasia (Dandy-Walker syndrome).
No mutations in ZIC2 or in other genes that cause HPE were identified, suggesting that mutation of ZIC2 is a rare cause of, or contributor to, RES associated with HPE.
Since human ZIC2 haploinsufficiency is a cause of holoprosencephaly, the Zic2kd/kd mice are regarded as an animal model for holoprosencephaly in humans.
The central nervous system malformations seen in patients with ZIC2 mutations ranged from alobar HPE (most common) to middle interhemispheric fusion defect (one case).