Scientific Frontiers in Developmental Toxicology and Risk Assessment (2000) / Chapter Skim
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2 Developmental Defects and Their Causes
2 Developmental Defects and Their Causes
Pages 17-25
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From page 17... ...
1997~. A1though infant mortality in the United States has declined by approximately 40% from 1968 to 1995, infant mortality attributable to major developmental defects has declined slightly less, by 34%, and, thus, the overall proportion of infant mortality due to developmental defects has increased from 14% to 22% from 1968 to 1995 (Ventura et al.
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From page 18... ...
1987~. The lessrecognized defects are of lesser clinical and cosmetic importance, and the estimate of their birth prevalence varies considerably because of substantial differences in definition and detection and the lack of a national systematic database for this information.
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From page 19... ...
Chromosomal aberrations in spontaneous abortions (8-12 weeks) Late fetal deaths after 20 weeks and stillbirths Major congenital anomalies at birth Minor developmental defects at birth Major developmental defects leading to infant death (before age 15 months)
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From page 20... ...
As noted before, developmental defects comprise all structural and functional deficits detected in the implanted embryo, fetus, neonate, infant, or child. The committee was asked to consider environmental agents that might cause developmental defects.
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From page 21... ...
It should be noted that much of the developmental toxicity testing on experimental animals was conducted at up to maternally toxic doses and, therefore, observed effects at those doses might not be the same as effects observed after exposure to environmentally relevant doses. It is not known how many of the 1,200 agents actually produce developmental defects in humans, and the figure is not obtainable by direct testing in humans.
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From page 22... ...
. In conclusion, although it is recognized that environmental agents can, and some do, act as developmental toxicants, it is still unclear how large a role these agents play in producing human congenital anomalies relative to other sources of developmental toxicants such as pharmaceuticals and food additives, and relative to intrinsic causes such as genetic differences.
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From page 23... ...
respiratory distress Cyclophosphamide Antineoplastic 4 mg/kg/d Limb and facial defects Diethylstilbestrol Synthetic estrogen 0.1-3 mg/kg/d Reproductive tract malformations and vaginal cancer Diphenylhydantoin Anticonvulsant 8 mg/kg/d Craniofacial defects, growth retardation, fetal loss, and intellectual deficit Treatment of .
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From page 24... ...
For example, EPA (1998a) conducted a study assessing data availability on close to 3,000 chemicals that the United States produces or imports at more than 1 million pounds per year and concluded that only 23% of those chemicals had been tested for reproductive and developmental toxicity.
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From page 25... ...
but not for others, making risk assessment a process requiring information about human diversity as well as toxicant action. A few percent (approximately 3%)
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