|The ovary and eggs of the female fetus are susceptible to damage by abnormal exposures. In both genders, gamete development begins in the mid first trimester. A female baby is born with all of her eggs.|
It is well established that drug and other chemical exposures can impair germ cell development (see Research page for some of the studies), particularly during certain sensitive periods of development when the DNA is relatively exposed. For example, prenatal exposure to the synthetic estrogen drug DES is known to affect the Third Generation's risk for cancer. Prenatal exposure to the synthetic endocrine disruptor BPA has been shown to disrupt both male and female germ cells in animal studies. And prenatal exposure to synthetic endocrine disrupting herbicides such as vinclozolin and dioxin (Agent Orange) are shown to have germline effects.
How do germ cells develop? Why are they vulnerable?
During the process of sexual differentiation of the embryo, at about 6 weeks gestation, primordial germ cells migrate to the embryonic genital ridge and then undergo a process called germline reprogramming over roughly weeks 6-18 of gestation. During this period, the DNA is stripped of most of the parental epigenetic markers and reprogrammed to achieve what is called totipotency. Totipotency basically refers to the ability of this single cell, in combination with another gamete encountered at fertilization, to differentiate into a complex organism of trillions of functionally different cells.
Germline development differs between males and females. In males, spermatogenesis begins in early gestation, but continues throughout the male's lifetime. In females, the eggs largely develop by about five months of gestation--a baby girl is born with all her eggs. Beginning in puberty, the eggs begin to undergo an additional process of division and ripening.
|Comparison of oogenesis and spermatogenesis. (|
Based on a survey of autism parents, we have found severity of neurodevelopmental symptoms to generally be more severe when the mother was exposed than if the father was exposed. That may be due to the fact that maternal germ cell development remains relatively arrested as compared to the male germ line after birth.
Although germ cells are the most important group of cells in the fetus, as they will give rise to the next and all succeeding generations, and even though their vulnerabilities are by now well documented, the FDA has never examined or required testing of germline impacts of pharmaceutical drugs. This is colloquially known as "The Oversight of the Century" or perhaps "The Mother of All Recklessness."