Congenital malformations make up an increasingly larger proportion of the causes of morbidity and mortality in newborns in developed countries. While there are many etiologies for these malformations, advances in epidemiologic approaches and reprotoxicology demonstrate that several common disorders such as cleft lip and/or palate (CLP), neural tube defects and congenital heart defects have a significant proportion of their causes due to complex gene-environment interactions. In parallel with this evolving knowledge of etiologies, advances in molecular genetics technologies and analytic approaches provide unique opportunities to identify both genetic and environmental contributions to these common disorders. In the 1930s Fogh-Andersen in Denmark first identified the genetic background of CLP. Through the following half century the ethnically homogeneous population of Denmark has been the platform for numerous comprehensive studies of the epidemiology and genetics of CLP. The large potential for doing molecular studies has, however, not been exploited to date. Dr. Murray at the University of Iowa has been involved in the gene mapping of several single gene craniofacial disorders and his group was the first to identify genetic associations in humans between clefting malformations and transforming growth factor alpha. This association has been confirmed in other settings but not all, and concern has been raised about the impact of ethnic distributions in the populations studied. More recently, new associations with TGFB3 have been identified and interactive effects of smoking with TGFA suggesting new windows into studies of gene- environment interaction. This proposal is based on several CLP ascertainment sources in Denmark. A nationwide case-control study of CLP was conducted in Denmark from 1991 to 1994 to collect information on environmental factors. Biological samples on 88 percent of the participating 322 CLP cases and 606 controls have been obtained through a PKU-bank which has been in operation since 1981. The PKU-bank will be the source of genetic information on an additional 1,000 CLP cases and 4,000 controls. Finally, a case-control study of approximately 200 CLP cases and 800 controls, including both genetic and environmental exposure information can be nested within a prospective study of 100,000 pregnancies to be conducted in Denmark in the period from 1995-1997. Based on Danish data-resources, American molecular expertise and joint analytic strengths, a Danish-American collaboration will characterize environmental, genetic and gene-environment interactions using association, linkage and logistic regression. This presents a unique opportunity to conduct a study with substantial power to detect new etiologies and confirm/refute current hypotheses of CLP. This will be of particular interest because the study is conducted in a relatively homogeneous population, which has constituted the basis of an important proportion of international CLP research.