Developmental Biology and Morphogenesis of the Face, Lip and Palate

1.1 Summary

The understanding of the natural history, clinical delineation, and clinical management of birth defects involving the face, lip, and palate has progressed significantly over the last 20 years and continues to do as we move further into the 21st century. Although human craniofacial morphogenesis is clearly the culmination of a very complex series of diverse and overlapping developmental events, all of these events can be categorized into four fundamental processes which span mammalian development and are evident in the earliest beginnings of the face and palate - normal and abnormal: (1) cell differentiation - the process through which the myriad of “building block” cell types invoked in facial morphogenesis are generated from the single-celled zygote; (2) morphogenesis - the process or set of processes through which the complex form of the face and its constituent cells, tissues, and organs will emerge in a timely fashion along patternable individual and population lines; (3) growth - the collective results of differentiation and morphogenesis; and (4) dysmorphogenesis and abnormal growth - this is the most exciting of the challenges we face today as we strive to understand how environmental influences interact with and cause changes in the expression of the genetic factors governing the behavior of those cells which will give rise to the entire human body, and especially the face and palatal regions. The treatment of defective genes is very much a part of the current clinical agenda dealing with craniofacial defects. The basic scientist, the dysmorphologist, the clinician, and, importantly, those with natural or acquired craniofacial defects have gained significant advantage from the critical use of available information coming from classical and experimental studies of human morphogenesis. These advantages will continue to increase as laboratory scientists and clinician scholars move rapidly together into the world of molecular and gene biology. These approaches should and will increase our knowledge base on the patterns and underlying causes of normal and abnormal craniofacial morphogenesis - and our patients will be all the better for it. However, most researchers and treatment providers well realize that the practical transfer of new biological information on normal and abnormal development flowing from the laboratory bench to the clinical bedside may be neither easy nor timely to achieve in the effective treatment and management of craniofacial abnormalities.