Syndromes associated with simple calvarial and complex craniofacial anomalies.

Central nervous system (CNS) development is a complex process of predetermined events that must occur in an ordered sequence to ensure normal ontogenesis. Various critical steps take place in a relatively short time (from the first few days to the first months of gestation). Both genetic and environmental insults may produce morphological defects. Early defects often result in nonviable embryos; later, complex craniofacial anomalies, mainly associated with brain damage, may be observed. The pathogenesis of congenital malformations is heterogeneous; sporadic cases are reported as well as recessive or dominant inheritance and chromosomal aberrations. Some of these syndromes have been identified as contiguous gene syndromes; the role of critical chromosomal regions and homeobox genes is discussed. Furthermore, these conditions present difficulties in regard to early diagnosis, surgical repair, and social impact.