Teratogenesis

Encyclopedia : T : TE : TER : Teratogenesis

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Teratogenesis is a medical term from the Greek, literally meaning monster-making, which derives from teratology, the study of the frequency, causation, and development of congenital malformations—misleadingly called birth defects. These include gross morphological abnormalities, such as cleft lip and/or palate, anencephaly, or ventricular septal defect, but may also include phenomenae such as increased risk of cervical cancer or discoloration of tooth enamel. These malformations can arise from genetic abnormalities of the fetus, from adverse environmental circumstances (termed teratogens or tetragens), or, frequently, from an unlucky combination of these factors. Teratogenesis has gained a more specific usage for the development of abnormal cell masses during fetal growth (see pregnancy), causing physical defects in the fetus. The study of teratogenesis is called teratology.

Known teratogens

The American College of Occupational and Environmental Medicine recognizes the following teratogens.[link]

• Ionizing radiation: atomic weapons, radioiodine, radiation therapy

• Infections: cytomegalovirus, herpes virus hominis I and II, parvovirus B-19, rubella virus (German measles), syphilis, toxoplasmosis, Venezuelan equine encephalitis virus

• Metabolic imbalance: alcoholism, endemic cretinism, diabetes, folic acid deficiency, hyperthermia, phenylketonuria, rheumatic disease and congenital heart block, virilizing tumors

• Drugs and environmental chemicals: 13-cis-retinoic acid (isotretinoin, Accutane), aminopterin and methylaminopterin, androgenic hormones, busulfan, captopril and enalapril (ACE inhibitors), chlorobiphenyls (PCBs), cocaine, coumarin anticoagulants, cyclophosphamide, diethylstilbestrol, diphenylhydantoin (Phenytoin, Dilantin, Epanutin) and trimethadione, etretinate, lithium, methimazole, organic mercury compounds, penicillamine, tetracyclines, thalidomide, trimethadione, valproic acid.

The status of some of the above substances (e.g. diphenylhydantoin) is subject to debate, and many other compounds are under varying degrees of suspicion. These include Agent Orange Note: Agent Orange contains 2,4-D, nicotine, aspirin and other NSAIDs, and birth control pills. Other compounds are known as severe teratogens based on veterinary work and animal studies, but aren't listed above because they have not been studied in humans, e.g. cyclopamine. Teratogenic effects also help to determine the pregnancy category assigned by regulatory authorities; in the United States, a pregnancy category of X, D, or C may be assigned if teratogenic effects (or other risks in pregnancy) are documented or cannot be excluded.

Isotretinoin (13-cis-retinoic-acid; brand name Accutane), often used to treat severe acne, is such a strong teratogen that just a single dose taken by a pregnant woman may result in serious birth defects. Because of this effect, most countries have systems in place to ensure that it is not given to pregnant women, and that the patient is aware of how important it is to prevent pregnancy during and at least one month after treatment. Medical guidelines also suggest that pregnant women should limit vitamin A intake to about 700 μg/day, as it has teratogenic potential when consumed in excess.

See also

• Carcinogen
• Mutagen
• Teratology

References

External links

• [The Teratology Society]
• [USPharmacist.com] summarizes the effect and time of susceptibility for several teratogens.
• An expansive [list of potential teratogens] from the Seventh Edition of "Dangerous Properties of Industrial Materials", Ed. Sax & Lewis, hosted by Purdue University.

 

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