Teratogenesis

Abstract

Teratology literally is the study of monsters (teras). Most workers, however, would consider the field to concern the study of abnormal development as caused by environmental agents, such as drugs, viruses, chemicals, and radiation. The overall incidence of congenital malformation in man has been reported to be 2% for major congenital malformations and 13.3% for a single minor anomaly not associated with serious problems. Wilson in 1973 categorized developmental defects according to etiology and found that 20% were due to a known genetic factor, 5% to a chromosomal aberration, and 5 to 9% to environmental causes, such as teratogens, that could be identified as the primary agents. The majority (65 to 70%) were due to unknown causes. In the group of developmental defects for which a teratogen could be identified, the teratogens were radiation (both accidental and therapeutic), viruses (such as the rubella virus), maternal diseases affecting fetal metabolism, drugs, and chemicals, drugs and chemicals comprising only 2 to 3% of the total incidence. In this presentation the scope of the problem of teratogenesis and the essentials of teratology are briefly reviewed. The teratogenicity of any compound is a reflection of a complex interaction of the compound with both the maternal and fetal tissues, the genetic background of the fetus, and the time sequence of gestational events. Under such circumstances the implication of a single compound as a teratogen is difficult, a fact reflected in the high percentage of congenital morphologic abnormalities for which no cause can be ascribed. Four compounds (thalidomide, anticonvulsants, alcohol, and folic acid antagonists) with a known teratogenetic effect on the musculoskeletal system are discussed, as is the role of the orthopedic surgeon in teratology.