Teratology
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Teratology (from the Greek teratos, meaning monster and logos meaning study) is the medical study of teratogenesis or grossly deformed individuals. Monster is a pejorative term for a grossly deformed individual.
Understanding Birth Defects and Deformity
Severely deformed humans rarely survive, although there have been some celebrated examples such as Joseph Merrick, known as "The Elephant Man". Some cases, such as conjoined twins, were formerly regarded as monsters, but are now candidates for surgery.
With greater understanding of the origins of these phenomena, this field now overlaps other fields of medicine, particularly developmental biology and embryology.
The birth of malformed fetuses has been well documented and the attitudes toward the infants and their parents varied according to the cultural state of the people and ranged from admiration to rejection and hostility.
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.
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.
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.