Role of Environment in Maternal Twins revealed by Numerous Methods under Many Conditions 149damage due to inadequate oxygen and blood flow. This can occur because the
shared blood circulation increases the chance of the blood flowing in the oppo-
site direction. Pumping blood back to the deceased twin deprives the surviving
twin of oxygen, fluids, and nutrients. The surviving twin may also be at risk of
restricted growth and other complications while in the womb. Most TTTS
twins, whether they receive treatment or not, will be born prematurely. TTTS is
an extreme form of unequal blood flow in maternal twins. There are four other
conditions that are generally ignored but present subtle situations of unequal
blood flows.
There are four types of twins in Figure 6.4 showing that in all cases – maternal
or fraternal – the blood supply is slightly uneven, making the exposure to
nutritional and environmental factors unequal with differential outcomes.
A comprehensive literature search has implicated several environmental factors
associated with the development of ASD. These include pesticides, phthalates,
polychlorinated biphenyls (PCBs), solvents, air pollutants, synthetic fragrances,
glyphosate (herbicide) and heavy metals, especially aluminum and organomer-
cury used in vaccines as adjuvant or preservative, respectively. Importantly, the
majority of these toxicants are some of the most common ingredients in cosmet-
ics and herbicides to which almost all of us are regularly exposed to in the form of
synthetic fragrances, face makeup, cologne, air fresheners, food flavors, deter-
gents, insecticides, herbicides, and vaccines, to name just a few. In this chapter we
describe various scientific data to show the role of environmental factors in ASD.
Role of Environment in Maternal Twins revealed by
Numerous Methods under Many Conditions
Monozygotic twin pairs provide a valuable opportunity to control for genetic
and shared environmental influences while studying the effects of non‐shared
or partially shared environmental influences, such as unequal blood supply to
each of the maternal twins. This unequal sharing or exposure to an environ-
mental chemical can result in unequal manifestation of numerous types in
genetically identical twins. There are literarily hundreds of reports in peer‐
reviewed scientific journals that show discordant monozygotic twins with
different phenotypes. In the following we describe only a few examples.
What Types of Discordance are Observed in Maternal Twins?
There are numerous dissimilarities that have been observed in identical twins.
One of the most interesting studies in the literature is that of right‐ or left‐
handedness. This right‐ and left‐handedness plays a great role in language and
learning. Häberling and colleagues [18] have examined the hemispherical
asymmetry and callosal morphology in monozygotic twins. Some 20–25% of