Testosterone and Male Gender Bias 9the Shikimate pathway is absent from human cells. However, human gut bac
teria do contain this pathway [34]. Inhibition of the Shikimate pathway by
glyphosate can have an adverse effect on gut bacteria and the gut microbiome
can change, and this has been associated with autism [35–37]. The Shikimate
pathway is essential in the synthesis of aromatic amino acids in both plants and
microbes. These amino acids are the precursors to all the monoamine neuro
transmitters, including serotonin, dopamine, and melatonin. Seneff claims that
this disruption of the Shikimate pathway in human gut microbes poses signifi
cant threats to health. Seneff further argues that glyphosate may be a key con
tributor to the autism epidemic in the USA [29–31].
She explains that glyphosate kills beneficial forms of bacteria in the gut and
causes an overgrowth of pathogenic bacteria, including Bacteroides fragilis
and Clostridium difficile [35]. This bacterium induces leaky gut syndrome and
produces p‐cresol, which is a phenolic compound and a known biomarker for
autism. A higher level of p‐cresol in urine is associated with autism [38].
Glyphosate exposure also disrupts sulfate synthesis, as well as sulfate trans
port from the gut to the liver and pancreas. Serum sulfate deficiency is another
known biomarker for autism. Defects in serotonin supply have been associ
ated with various mood disorders. Seneff argues that glyphosate’s disruption
in the synthesis of serotonin can lead to a defective serotonin transporter
gene, which would decrease the bioavailability of serotonin for neuronal sign
aling. This decreased supply of serotonin in the brain is a major feature of
autism [38]. The absence of the Shikimate pathway in human cells and the
presence of the pathway in beneficial forms of bacteria in the gut (Bacteroides
fragilis) should not be taken lightly, since the total number of these bacteria in
our gut is 10 times higher than the total number of cells in an adult human
body. The vital questions are how does this mechanism cause autism and do
various herbicides cause other adverse effects? The answers to these ques
tions have been the center of numerous investigations and many respectable
investigators are looking at these questions. In brief, we can state that glypho
sate causes profound alteration of the gut microbial environment and studies
have confirmed that this herbicide may be associated with ASD [36,37].
However, it should be noted that Seneff ’s hypothesis does not explain the
gender bias in ASD [29,39,40].
Testosterone and Male Gender Bias
The third element that could help explain male gender predominance in
autism is still a hypothesis. There is a commonly recognized, but inexplica
ble, bias toward males in classical autism, with a ratio of ~5:1 in ASD [1–3,41],
and in Asperger syndrome, the ratio is ~10:1 [1–3]. Aside from the familiar
dogma that genetic components form the basis of ASD, not a single gene has