14 Introduction to Autism Spectrum Disorders
Musk ambrette, a fragrance ingredient that was banned in the European
Union although allowed in the USA, causes myelin sheath production in addi
tion to distal axonal degeneration [18,70,72,73].
Even if one considers the high fetal testosterone levels present during the
early stages of gestation, this still does not explain the rapid rise of ASD in
recent decades; one must also consider the impact of synthetic chemicals that
behave like hormones, particularly like fetal testosterone or that bind to andro
gen receptors in the fetal brain and can enter the blood circulation of the devel
oping fetus [63,64]. We maintain that numerous synthetic fragrances contain
testosterone‐like hormones [63,64]. Chlordane was widely used in termite
prevention in buildings in the USA starting in the 1960s. In 1979 its use inside
homes was banned, and then in 1983 it was also banned as a soil treatment for
areas underneath homes [78]. Then, in 1988, citing concerns about environ
mental degradation and harm to human wellbeing, the United States
Environmental Protection Agency (US EPA) proclaimed a complete ban on
chlordane [78].
At this point it is pertinent to ask why the three factors mentioned in the
preceding sections (synthetic fragrances, glyphosate, and fetal testoster
one‐like chemicals or EDCs) may be contributing to ASD development in
children while they do not seem to have any apparent adverse effects in
adult brains. An adult body has a minuscule degree of cell differentiation
taking place in the brain compared with the degree of differentiation in a
rapidly developing fetal body, especially during weeks 4–24 of gestation.
The majority of adult brain cells are already differentiated and only very
few types of cells are still regenerating but no longer differentiating. These
include olfactory neurons and a few cell types in the amygdala that are
involved in solidifying our permanent memories (we will return to this
later in Chapter 7 explaining why Alzheimer’s patients lose their olfaction
ability and lose their memory); at birth our muscle cells are already dif
ferentiated. The major cell types that are still regenerating are neutrophils,
immune cells, glandular and other epithelial cells. Our immune cells are
already built, and B and T lymphocytes are regenerating and differentiat
ing from pre‐terminal to terminal phases constantly. These differentia
tions are not the same as with the primordial and progenitor cells that
differentiate in the early stages of human fetus development and especially
in the fetal brain neurons. Therefore, any environmental agents that inter
fere with fetal brain development can cause major adverse effects even
after birth. The most vulnerable period is during weeks 4–24 of gestation.
There are many external agents that can inflict damage to the DNA of dif
ferentiating and rapidly replicating cells in an adult immune system but
adult muscle cells have already completed their differentiation during the
late fetal period. Thus, they are in no real danger, but glandular and epi
thelial cells are vulnerable. There is little surprise that the incidence of