[Developmental abnormalities in humans]

Recently, tremendous advances have been made in our understanding of pre- and perinatal death and congenital anomaly, but many aspects of the field remain unknown and require the continued collaboration of workers in many clinical and basic science disciplines. Most of mankind dies before, not after birth, mostly due to chromosome abnormalities arising during pregenesis. A few trisomy 13 and 18 cases survive till birth by virtue of placental mosaicism; even trisomy 21 is an 80% prenatally lethal and a postnatally sublethal syndrome. Most aneuploid individuals surviving postnatally have sex chromosomes abnormalities (47,XXY, 47,XYY, 47,XXX). Until recently the term "monsters" was applied to many abnormalities of blastogenesis--i.e. the disruptions and malformations arising during the first 4 weeks of embyronic development (till the end of mesoderm formation). This includes not only acardia/acephaly, but also holoprosencephaly, sirenomelia, gross defects of cord, body wall and -stalk formation and conjoined twins, but also non-conjoined monozygotic twins with apparent high prenatal mortality and a high incidence of midline anomalies. One of the most important recent insights has been that associations, e.g. the VACTERAL association, and the relatively characteristic combination of anomalies seen in infants of diabetic mothers, represent disruptions of blastogenesis. The latter represent a particularly satisfying development in the field since it has been shown that control of the woman's blood sugar levels before, during and after conception helps to reduce the high incidence of defects of blastogenesis in infants of diabetic mothers. Most malformations arise during organogenesis in secondary or epimorphic fields and mostly represent anomalies of incomplete, less commonly of abnormal differentiation. An important distinction must be made between mild malformations (all-or-none defects of organogenesis) which are relatively innocuous and common in the population but never normal, and minor anomalies which are graded defects of phenogenogenesis (i.e. of the developmental processes during the fetal period (weeks 8-10 p.c.), and the most frequent anomalies in aneuploidy syndromes with resulting loss of family resemblance.(ABSTRACT TRUNCATED AT 400 WORDS)