[Environment and genetics in the etiology of cleft lip and cleft palate with reference to the role of folic acid].

The combined birth prevalence of cleft palate [CP] and cleft lip with or without cleft palate [CL(P)] in Europe is approximately one in 700 with characteristic regional variations. Orofacial clefting (OC) is therefore now one of the most frequent congenital anomalies, with a higher birth prevalence that Down's Syndrome or Neural Tube defects, but still lower than cardiovascular malformation. Babies with OC require a multidisciplinary medical approach, surgery and rehabilitative treatments over time. This means an important effort in terms of social organization as well as economical costs for the health care system. In Italy, the health care costs for approximately 800 children born with orofacial clefting per year has been estimated at around 150 billion Lire (80 million Euros). The etiology of OC is complex and heterogeneous both for isolated and associated defects; causes linked to environment, genetics and gene-environment interaction are known, although there is still a lot to do, especially in clarifying the role of genetics in producing susceptibility to the environment. Four categories of genes for which there are results suggestive of a genetic susceptibility to OCs are: 1) genes expressed in a particular area of the embryo or in a particular period of the palatine arch development, such as the transforming growth factors alpha and beta (TGF alpha, TGF beta 2, TGF beta 3); 2) genes having biological activities linked to the OC's pathogenesis without direct involvement (e.g. the retinoic acid receptor (RARA), the methylenetetrahydrofolate reductase receptor (MTHFR) and the folic acid receptor (FOLR1); 3) genes or locus identified in experimental animals as the homeotic genes MSX-1 and MSX-2; 4) genes involved in the interaction with the xenobiotics metabolism as those in P-450 cytochrome system. Several environmental factors have been implicated in the OC etiology; among those, the folic acid supplementation during the periconceptional period that was found effective in the prevention of neural tube defects. In fact, folic acid deficiency may be responsible for different malformations through a common mechanism that interferes with the embryonic development, depending on the maternal or embryo genotype. Further investigation is required to study in depth how the genotype would modify the role of environmental factors like folic acid. Well-designed and conducted epidemiological studies seem to be able to give worthwhile information. Studies carried out in Europe on these issues are a few, particularly those on gene-environment interaction. Recent results obtained in molecular biology and the availability of wealth of data can allow to perform ad hoc investigations, being important not only for the basic research but also for their public health implications. For this objective a specific scientific network at the European level has been set by the European Science Foundation (ESF), whose first step will be to establish consistent case ascertainment and data collection across Europe and to develop standardized protocols and methods of analysis. It is hoped that in the longer term such multicentre collaborative research will enable combined analysis and lead to the identification of genetic susceptibility to certain environmental factors, including nutrition. Such studies would inform the current debate about the efficacy of folic acid and other nutritional factors in prevention of disease in the developing embryo. Subsequent public health measures targeted according to risk might reduce the prevalence of disorders such as orofacial clefting.