Primary midline developmental field. I. Clinical and epidemiological characteristics

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Abstract
Opitz [BD: OAS XXIX(1): 3-37, 1993] has postulated that during early blastogenesis the entire embryo represents a single morphogenetic unit, the primary field. During this period, beginning gastrulation, the most important events are the formation of the midline and the mesoderm. Consequently, one could expect that dysmorphogenetic reactions of the primary field are likely to disturb more than one of the essential events of blastogenesis, such as fusion, lateralization, decussation, segmentation, morphogenetic movements, asymmetry formation, etc. I have used the 20,891 liveborn malformed infants identified by the Spanish Collaborative Study of Congenital Malformations (ECEMC) to analyze the concept of the primary field defect (DFD). The malformed children were separated into 4,679 children with only midline defects, 1,592 children with midline plus other non-midline anomalies, and 14,620 babies without midline defects. Sex, twinning, neonatal death, parental consanguinity, and other malformed first degree relatives in the family were analyzed in each group. Different defects were selected as indicators of specific morphogenetic events of blastogenesis. Cardiac and neural tube defect were selected as indicators of fusion anomalies; agenesis/hypoplasia of the corpus callosum were included as example of decussation defect; cyclopia as representation of the alteration of lateralization; vertebral defects as indicators of anomalies of segmentation; intestinal malrotation and omphalocele as representatives of the alteration of the morphogenetic movement; and, finally, infants with asplenia, polysplenia, dextrocardias, transposition of great vessels, visceral transposition, and situs inversus totalis were grouped to allow an analysis of alteration of the normal body asymmetry. The results of this analysis demonstrate, from an epidemiological standpoint, that the infants with midline anomalies have alteration of the normal body asymmetry more frequently than infants without midline defects. Children with midline anomalies have more severe malformations with high lethality, associated with twinning, without sex differences in occurrence, and with low recurrence risk, than do infants without midline defects, as was suggested by Opitz [BD: OAS XXIX(1): 3–37, 1993].