Molecular genetics of holoprosencephaly.

Holoprosencephaly (HPE) is a common developmental defect of the human forebrain and midface. Pathological studies have identified different categories of severity of the brain and craniofacial malformations observed in HPE, although the variable clinical spectrum of HPE extends in unbroken sequence from alobar HPE and cyclopia to clinically unaffected carriers in familial HPE. The etiology of HPE is extremely heterogeneous including both environmental and genetic causes. Here we focus on molecular aspects of HPE in light of the recent identification of some of the genes causing human HPE and other candidate genes involved in forebrain development, through different approaches, such as positional cloning and functional cloning, based on animal models. These approaches will aid in the identification of additional genes involved in HPE and in a better understanding of the molecular genetics of brain development.