Primary developmental field. III: Clinical and epidemiological study of blastogenetic anomalies and their relationship to different MCA patterns.

Opitz [1993: BD:OAS XXIX (1):3-37] suggested that during blastogenesis the entire embryo constitutes a developmental field, i.e., the primary developmental field. Based on this principle, he postulated that a single "hit," that during late morphogenesis would cause a monotopic malformation, during blastogenesis would produce a polytopic malformation or an association. Lubinsky [1986: Am J Med Genet [Supp1]2:6-16] had stated previously that "since the embryo develops in an integrated manner, organized and differentiating spatially, temporally, and in an epimorphically hierarchical manner, disturbances result in nonrandom patterns of anomalies." He then concluded that "associations are derivatives of causally nonspecific disruptive events acting on developmental fields." These concepts, confirmed by our epidemiological observations [Martínez-Frías, 1994: Am J Med Genet 49:45-51], imply that some associations are, by definition, abnormalities of blastogenesis that is, that their component congenital anomalies are produced by events occurring during the first 4 weeks of development. We present an analysis of the characteristics of blastogenetic anom-alies and their relationship with midline abnormalities, as well as with the schisis and VACTERL associations.