Pathogenetic analysis of certain developmental and genetic ectodermal defects.

It is postulated that, in the nevoid basal cell carcinoma syndrome, independent mosaic pleiotropic action of the mutant gene on morphogenesis and histogenesis produces primary malformations of midline and nonmidline structures and dysplasias more or less highly predisposed to cancer development. However, in focal dermal hypoplasia and the Bartsocas-Papas syndrome, it is highly tempting to postulate that embryonic dysplasias, ie, breakdown or necrosis of ectoderm, especially in the region of the Ekdodermring, are responsible for the production of many of the congenital anomalies seen in these patients, and that these anomalies more likely represent sequences rather than primary malformations. The sequences in the type 1 fetal epidermal dysplasias probably represent mucosal breakdown, producing various upper gut atresias and an epidermal "disease" with loss of epidermis and many severe secondary consequences. Polyhydramnios, micrognathia, "arthrogryposis," reduced fetal growth, and short umbilical cord are other consequences of fetal hypokinesia due to stiff skin in the type 2 fetal epidermal dysplasias, with severe muscle involvement in the Hutterite-Mennonite type possibly responsible for additional fetal hypokinesia. Thus it seems likely that embryonic and fetal dysplasias can now be held responsible, directly and indirectly, for a fascinating variety of human congenital anomalies.