Teratology
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Teratology (from the Greek τέρᾰς (genitive τέρᾰτος), meaning monster, or marvel and λόγος, meaning word, speech) as early as 17th century referred to a discourse on prodigies and marvels, of anything so extraordinary as to seem abnormal. In 19th century, it acquired a meaning closer related to biological deformities, mostly in the field of botany. Currently, its most instrumental meaning is that of the medical study of teratogenesis, congenital malformations or grossly deformed individuals. Monster is a pejorative term for a grossly deformed individual, although it is intersting to note, that etymologicaly this word is related to demonstration, and used to simply mean something worth looking at, for being unusual, without necessarily being pejorative. Another term for this is dysmorphology, which literally means "the study of abnormal form".
Teratology as a medical term was popularized in the 1960s by Dr. David W. Smith (1926–1981) of the University of Washington Medical School, one of the researchers who became known in 1973 for the discovery of Fetal alcohol syndrome. With greater understanding of the origins of birth defects, the field of teratology now overlaps with other fields of medicine, including developmental biology, embryology and genetics.
[edit] Understanding birth defects and teratology
Birth defects are known to occur in 3-5% of all newborns. They are the leading cause of infant mortality in the United States, accounting for more than 20% of all infant deaths (CDC 2003). Seven to ten percent of all children will require extensive medical care to diagnose or treat a birth defect (Dicke 1989). Although significant progress has been made in identifying etiologic causes of some birth defects, approximately 65% have no known or identifiable cause (O'Rahilly 1996).
It was previously believed that the mammalian embryo developed in the impervious uterus of the mother, protected from all extrinsic factors. However, after the thalidomide disaster of the 1960's, it became apparent and more accepted that the developing embryo could be highly vulnerable to certain environmental agents that have negligible or non-toxic effects to adult individuals.
Along with this new awareness of the in utero vulnerability of the developing mammalian embryo came the development and refinement of The Six Principles of Teratology which are still applied today. These principles were developed by James G. Wilson and are as follows:
- Susceptibility to teratogenesis depends on the genotype of the conceptus and the manner in which this interacts with environmental factors;
- Susceptibility to teratogenic agents varies with the developmental stage at the time of exposure;
- Teratogenic agents act in specific ways (mechanisms) on developing cells and tissues to initiate abnormal embryogenesis (pathogenesis);
- The final manifestations of abnormal development are death, malformation, growth retardation, and functional disorder;
- The access of adverse environmental influences to developing tissue depends on the nature of the influences (agent);
- Manifestations of deviant development increase in degree as dosage increases from the no-effect to the totally lethal level.
Studies designed to test the teratogenic potential of environmental agents use animal model systems (e.g., rat, mouse, rabbit, dog, and monkey). Early teratologists exposed pregnant animals to environmental agents and observed the fetuses for gross visceral and skeletal abnormalities. While this is still part of the teratological evaluation procedures today, the field of Teratology is moving to a more molecular level, seeking the mechanism(s) of action by which these agents act. In addition, pregnancy registries are large, prospective studies that monitor exposures women receive during their pregnancies and record the outcome of their births. These studies provide information about possible risks of medications or other exposures in human pregnancies.
Understanding how a teratogen causes its effect is not only important in preventing congenital abnormalities but also has the potential for developing new therapeutic drugs safe for use with pregnant women.
[edit] Teratology education
It is estimated that 10% of all birth defects are caused by a prenatal exposure or teratogen (O'Rahilly 1996). These exposures include, but are not limited to, medication or drug exposures, maternal infections and diseases, and environmental and occupational exposures. Teratogen-caused birth defects are potentially preventable. Studies have shown that nearly 50% of pregnant women have been exposed to at least one medication during gestation (Bracken 1981). An additional study found that of 200 individuals referred for genetic counseling for a teratogenic exposure, 52% were exposed to more than one potential teratogen (King 1986).
Despite scientific advances in clinical teratology, exposures prior to and during pregnancy still cause great anxiety and misunderstanding among both the public and health care professionals. Teratology Information Services (TIS) are comprehensive and multi-disciplinary resources for medical consultation on prenatal exposures. Pregnant women, health care providers, and the general public may call the toll-free number of their local TIS to receive up-to-date, evidence-based information about exposures during pregnancy.
Teratogens come from many sources and exposure to these agents while pregnant may cause congenital abnormalities. Therefore, the best way to prevent birth defects is through education and research. Researchers are currently investigating the possible causes of many teratogenic agents to determine their mechanism(s) and site(s) of action. This field is still in its infancy and continuously growing in importance.
[edit] See also
- Summa izbu - a set of Mesopotamian omen texts about Teratology.
- Congenital abnormalities
[edit] External links
- http://www.teratology.org/
- http://www.etsoc.com/
- http://www.otispregnancy.org/ Organization of Teratology Information Specialists
[edit] References
- Aase, J.M. (1990), Diagnostic Dysmorphology. Plenum: New York.
- Bracken, M. and Holford, T. (1981). Exposure to prescribed drugs in pregnancy and association with congenital malformations. Obstet Gynecol. 58:336.
- CDC, Birth Defects. Retrieved April 1, 2003, from http://www.cdc.gov/ncbddd/bd/
- Dicke, JM. (1989). Teratology: principles and practice. Medical Clinics of North America. 73(3):567-82.
- King, C. 1986. Genetic counseling for teratogen exposure. Obstet Gynecol. 67:843.
- O'Rahilly, R. and Muller, F. (1996). Human Embryology and Teratology, 2nd ed. John Wiley and Sons, Publications, New York.
