Developmental toxicity

Developmental toxicity is any structural or functional alteration, reversible or irreversible, which interferes with homeostasis, normal growth, differentiation, development or behavior, and which is caused by environmental insult (including drugs, lifestyle factors such as alcohol, diet, and environmental toxic chemicals or physical factors). It is the study of adverse effects on the development of the organism resulting from exposure to toxic agents before conception (either parent), during prenatal development, or post-natally until puberty. The substance that causes developmental toxicity from embryonic stage to birth is called teratogens. The effect of the developmental toxicants depends on the type of substance, dose and duration and time of exposure. Developmental toxicity is any structural or functional alteration, reversible or irreversible, which interferes with homeostasis, normal growth, differentiation, development or behavior, and which is caused by environmental insult (including drugs, lifestyle factors such as alcohol, diet, and environmental toxic chemicals or physical factors). It is the study of adverse effects on the development of the organism resulting from exposure to toxic agents before conception (either parent), during prenatal development, or post-natally until puberty. The substance that causes developmental toxicity from embryonic stage to birth is called teratogens. The effect of the developmental toxicants depends on the type of substance, dose and duration and time of exposure. Certain Pathogens are also included since the toxins they secrete are known to cause adverse effects on the development of the organism when the mother or fetus is infected. Developmental toxicology is a science studying adverse developmental outcomes. This term has widely replaced the early term for the study of primarily structural congenital abnormalities, teratology, to enable inclusion of a more diverse spectrum of congenital disorders. Typical factors causing developmental toxicity are radiation, infections (e.g. rubella), maternal metabolic imbalances (e.g. alcoholism, diabetes, folic acid deficiency), drugs (e.g. anticancer drugs, tetracyclines, many hormones, thalidomide), and environmental chemicals (e.g. mercury, lead, dioxins, PBDEs, HBCD, tobacco smoke). The first-trimester exposure is considered the most potential for developmental toxicity. Once fertilization has taken place, the toxicants in the environment can pass through the mother to the developing embryo or fetus across the placental barrier. The fetus is at greatest risk during the first 14th to 60th day of the pregnancy when the major organs are being formed. However, depending on the type of toxicant and amount of exposure, a fetus can be exposed toxicant at any time during pregnancy. For example, exposure to a particular toxicant at one time in the pregnancy may result in organ damage and at another time in the pregnancy could cause death of the fetus and miscarriage. There are a number of chemicals, biological agents (such as bacteria and viruses), and physical agents (such as radiation) used in a variety of workplaces that are known to cause developmental disorders. Developmental disorders can include a wide range of physical abnormalities, such as bone or organ deformities, or behavioral and learning problems, such as a mental retardation. Exposures to some chemicals during pregnancy can lead to the development of cancer later in the life of the child and are called transgenerational carcinogens. Exposure to toxicants during the second and the third trimester of a pregnancy can lead to slow fetal grown and result in low birth weight. Researchers have been able to ascertain toxicity associated with abnormal development with new breakthrough in developmental biology. Recognition of the developmental toxic effects of various molecules is recent development. Terato means monster in Greek. Until the 18th century, the preformism theory was accepted by which abnormal growth was considered as deformations. The 19th century saw developmental in descriptive embryology where abnormalities were now considered as malformations or errors during a developmental process giving rise to the concept of teratogenesis. By the 20th century, the concept of epigenesis the interaction between a genetic program and environment was established and in the second half of the 20th century researchers had evidence that environmental factors can cause malformations and even trans-generational effects. One of the first environmentally induced congenital malformations in humans were recognized as a result of maternal irradiation. Hiroshima (’53), and Nagasaki (’55), had ascertained this fact for the first time based on the records of births occurring before May 31, 1946, but after the atomic bombing (August 6, 1945, in Hiroshima; August 9th, 1945 in Nagasaki). A 20% increase in microcephaly frequency was seen in children with in-utero radiation exposure during the first trimester of the pregnancy (Miller 1956, 1968). Sensitivity to these radiations was seen to be predominantly high during the 7-15th week of gestation.