TERATOLOGY

Definition

   Teratology is the study of birth defects (structural, functional, and physiological). Wikipedia defines it as the study of abnormalities of physiological development. These abnormalities are caused by teratogens, which are  substances that may cause birth defects via a toxic effect on an embryo or foetus.

Origin of the word

   The term teratology originates from the Greek τέρας teras (genitive τέρατος teratos), meaning "monster" or "marvel", and λόγος logos, meaning "the study of".

Principles of teratology

   These principles were put forth by Jim Wilson in 1959, in his monograph 'Environment and Birth Defects'. They guide the study and understanding of teratogenic agents and their effects on developing organisms. They include:

(i) Susceptibility to teratogenesis depends on the genotype of the conceptus and the manner in which this interacts with adverse environmental factors.

(ii) Susceptibility to teratogenesis varies with the developmental stage at the time of exposure to an adverse influence. There are critical periods of susceptibility to agents and organ systems affected by these agents.

(iii) Teratogenic agents act in specific ways on developing cells and tissues to initiate sequences of abnormal developmental events.

(iv) The access of adverse influences to developing tissues depends on the nature of the influence. Several factors affect the ability of a teratogen to contact a developing conceptus, such as the nature of the agent itself, route and degree of maternal exposure, rate of placental transfer and systemic absorption, and composition of the maternal and embryonic/fetal genotypes.

(v) There are four manifestations of deviant development (Death, Malformation, Growth Retardation and Functional Defect).

(vi) Manifestations of deviant development increase in frequency and degree as dosage increases from the No Observable Adverse Effect Level (NOAEL) to a dose producing 100% Lethality (LD100).

Conclusion

   Teratology is moving to a more molecular level, seeking the mechanism 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. The study of teratogens and how they act is therefore of great importance in the medical field.