Why Is There a “Spectrum” in Autism? 21
When describing a teratogen, one may think of three basic characteristics:
- A given teratogen may be organ specific or cell receptor specific (i.e., like
EDCs or synthetic chemicals) [63,64]. - It may be species specific meaning only certain species may express recep
tors for those teratogens. - It can be dose specific meaning a very tiny dose may kill certain specific cells
at a certain stage of gestation but may require much higher dose at a differ
ent stage of gestation (many synthetic chemicals fall into this group).
Figure 1.11 illustrates the concept.
The last point is where we think the “spectrum” manifests in ASD. The syn
thetic chemicals (i.e., fragrances, herbicides/pesticides and EDCs) hit specific
brain progenitor cells in a developing fetus. For example, if a given chemicals
enters a fetus brain and only binds to oxytocin receptors or olfactory neurons
and kills those cells in the very early stages of gestation, it will result in total or
almost complete deletion of those progenitor cells that are involved in social
communication or olfaction (smell). In the early stage of gestation (i.e., 8 weeks
of gestation), there may be only a few progenitor neurons that would ultimately
represent the faculties of communication or olfaction. However, if the same
chemical enters the fetal brain in the later stages of development (i.e., 24 weeks
of gestation) at the same dose, then we would expect that there would be mil
lions of partially differentiated second or third progenitor neurons for oxytocin
receptors or olfaction receptors, so they may only be partially damaged – layers
of creating a “spectrum” of deficit (see Chapters 3 and 4). One can think of this
in terms of how an oak tree grows. If one kills the seed, it will be akin to a
miscarriage; if one cuts off a large branch when the tree is just 30 cm tall
(equivalent to 15 weeks of fetal gestation), then the tree will be a lopsided oak
(equivalent to showing some degree of neurologic deficit). However, if one cuts
off multiple branches when the tree is 1 year old (32 weeks of gestation), the
tree may grow almost normally and those branches will regrow (equivalent toa
relatively small adverse effect being observed).
Presented in a simplistic fashion, Figure 1.12 represents the changes just
described.
Extreme disability Autism Asperger syndrome
Figure 1.11 A metaphoric illusion of ASD to colors of light.