Holoprosencephaly: new concepts.

Holoprosencephaly represents a broad spectrum of malformations resulting from a lack of separation of the structures of the forebrain. Recent discoveries in the fields of genetics and developmental neurobiology have advanced our knowledge of this complex disorder. By combining this basic-science knowledge with observations of brain morphology, we can better understand the embryology and genetic factors that influence brain development and, ultimately, form more accurate classification systems and stratification measures for predicting patient outcome.