Unusual variant of holoprosencephaly in monosomy 13q.

The clinical phenotype related to the terminal deletion of the long arm of the chromosome 13 (the so-called 13q- syndrome) includes a considerable number of malformations, especially of the brain. This report describes five cases of a cerebral midline anomaly that leads to a particular clover-shaped type of holoprosencephaly in 13q- fetuses at different stages of the second and third trimesters of gestation. Our cases are compared to those in literature reviews. This malformation has only been described by computer tomography and magnetic resonance imaging in eight children of various ages and has been called "middle interhemispheric fusion" or syntelencephaly. Recently, the human gene ZIC2, the mutation of which leads to holoprosencephaly, has been mapped to the long arm of chromosome 13. on band q32. These findings suggest that this particular type of holoprosencephaly may be related to ZIC2 gene loss of function.