EVALUATION OF GENETIC AND ENVIRONMENTAL COMPONENTS OF ORODENTAL ANOMALIES IN BIRTH DEFECTS

Abstract

Birth defects can be defined as any deviation from normal development present since birth which may be manifested at any stage of development, prenatal, at birth, neonatal, or later in life. (Temtamy et al., 1993). Congenital malformations are developmental defects apparent on inspection at the time of birth or in the neonatal period. They can be genetically determined due to gene mutations or chromosomal aberrations or due to environmental factors or the combination of both.(Chaturvedi and Banerjee, 1993) The frequency of birth defects in any population is one of the most important parameters which need to be assessed periodically for early monitoring of teratogenic and mutagenic exposure and investigate the relative burden of genetic versus environmental etiology (Temtamy et al., 1993). About 3% of human newborns have a congenital anomaly. They may present as microscopic change or as gross alterations recognizable by clinical examination of the body. (Emery and Rimoin,1990) Teratogenesis is environmental interference with normal prenatal development between conception and birth in contrast to genetic interference which is predetermined before the time the sperm and the ovum unite to form the zygote. Our knowledge about the causes of congenital defects are quite limited (Shepard, 1988). To distinguish between genetic and environmental interference: A careful prenatal history, detailed pedigree, population studies biochemical studies should be carried out. One of the primary considerations in medical genetics is evaluation of the recurrence risk - that is the risk that a genetic disorder in a patient will also affect other family members. (Hanson, 1990) Among disorders caused wholly or partly by genetic factors four types are recognized: 1. Single-gene disorders. 2. Chromosomal disorders. 3. Multifactorial disorders. 4. Somatic cell disorders. About 20% of birth defects are associated with gene mutation and another 5% with chromosomal aberrations. Less than 10% of the remaining anomalies are known to be due to teratogenic agents (Hanson, 1990). Since birth defects caused by teratogenic agents are preventable, it is of utmost importance to recognize prevalent agents in our country and to avoid exposure of the mother to them during critical periods of fetal development (Shepard, 1988). Normal growth and development are finally regulated by a complex interaction of hormonal influence, tissue responsiveness and nutrition. Metabolic and genetic signals can modulate these responses. Thus normal growth depends upon adequate administration and absorption of food, a series of genetic and environmental circumstances, good health, emotional well-being and an intact endocrine system including normal neurohormonal regulation (Syllabus, 1990). So, the main values of our knowledge of the genetics of orodental anomalies are for proper genetic counseling and for diagnosis. In a patient presenting with an orodental anomaly it is important to know whether the anomaly is genetically determined or not and whether it is associated with other malformations in different parts of the body. These are the main points that will affect the management and prognosis of the patient.