How does autism affect the brain? This is a question that’s motivated researchers in pursuit of understanding the autism spectrum disorder (ASD) for years. We already know that ASD is a neurodevelopmental disorder that impairs an individual’s ability to communicate, interact socially, comprehend, and behave the way neurotypical individuals do. However, pinpointing ASD’s root cause may be aided by an exploration into the neurodegeneration hypothesis. This hypothesis, which suggests that ASD can be regressive, stems from reports that some autistic children acquired neurological impairments after certain skills were developed. In other words, rather than being born with the inability to communicate, interact, and comprehend in a typical fashion, children can acquire these skills and then lose them. This regression suggests that development is somehow interrupted, rather than impaired from birth. ASD regression is said to affect anywhere between 15% and 65% of individuals on the autism spectrum. Whether autism can be officially considered a neurodegenerative disorder has remained under debate.
Recent research from David Geier, Mark Geier, Janet Kern, and Lisa Sykes probes deeper into the neurodegeneration hypothesis in their 2013 paper, “Evidence of Neurodegeneration in the Autism Spectrum Disorder.” According to the researchers, when synthesizing an array of related research, it can be determined that there is enough credible evidence to conclude ASD can be a neurodegenerative disorder.
To start, widespread post-mortem evaluations of individuals with ASD demonstrate that these individuals experienced a loss of neuron cells (a defining characteristic of neurodegeneration). It’s also been found that individuals with ASD have fewer neuron cells and pyramidal cells in their amygdala than control subjects. Further, the role of microglia, non-neuron cells that maintain homeostasis in the body and can contribute to the development of other neurological disorders, may also point to neurodegeneration in ASD individuals. Studies have found that these microglia can be responsible for the dissolution of neurons, and can also produce toxic cytokines that can damage neurons and lead to neurodegeneration. Findings from a number of recent studies support the hypothesis that microglia activation could be evidence of degeneration, given that many regions of the brain with activated microglia, most prominently the cerebellum, were found to be inflamed in those with ASD.
The toxins that can be released by microglia activation, which include nitric oxide, reactive oxygen species, and a number of proinflammatory cytokines, also point to neurodegeneration. These inflammatory cytokines have been found to be present in other neurodegenerative disorders, including Alzheimer’s disease, Parkinson’s disease and Multiple Sclerosis, yet have in appeared in the spinal cords and brains of those with ASD, too. An increase in the production of ROS (reactive oxygen species), is also prominent in neurodegenerative diseases like ALS, Parkinson’s disease and Alzheimer’s disease, as ROS ultimately results in the loss of neuron cells. As with individuals of these neurodegenerative disorders, those with ASD also maintain high levels of cell death as a result of oxidative stress.
Studies have also revealed that an oxidative stress damage marker that appears in the brains of those with neurodegenerative disorders, 8oHdG, appears at 63% higher levels in those with ASD than in control subjects.
While “Evidence of Neurodegeneration in Autism Spectrum Disorder” presents compelling evidence that ASD can in fact be considered a neurodegenerative disorder, as the researchers assert, its link to toxic exposures must also become more widely studied and accepted. Prolific research has suggested toxins can trigger the onset of ASD, yet this research has been largely dismissed by institutions like the World Health Organization because ASD is not currently classified as a neurodegenerative disorder. With additional research and awareness, this may soon change.