Autism is defined by a set of symptoms which includes impaired social interactions, repetitive or restrictive behaviors, and language abnormalities. According to the CDC, in 2014 1 in 59 children was identified as having autism spectrum disorder (ASD), a 250% increase from a similar survey done in 2000.
ASD poses an issue for society, “The total costs per year for children with ASD in the United States were estimated to be between $11.5 billion – $60.9 billion (2011 US dollars). This significant economic burden represents a variety of direct and in-direct costs, from medical care to special education to lost parental productivity” (cdc.gov). The total cost per year is projected to increase as cases of ASD increases.
Autism Spectrum Disorder: The Basics
ASD is very complicated (for further details, check out other blog posts on this site!) and has many moving parts already, and scientists do not even know the entire story yet. But here are some factors that are linked to autism:
Connectivity of Neurons
The brain is commonly likened to a circuit: neurons are wires and the chemicals are like electricity flowing through the wires. But a neuron is a wire that makes connections to more than one output. In autism, many neurons are not making good connections to their target outputs. Individuals with autism have too many possible outputs on the neuron which gets in the way of sending a clear message; this is a result of improper synaptic pruning. This essentially causes noise in the circuit by allocating the signal to the incorrect neurons thereby dampening the signal to the target output.
Immunity
The immune system is extremely important in keeping us healthy by fighting off germs and diseases. However, when the immune system is active when we are not sick, that poses problems for our bodies. Our immune system releases chemicals that tell our bodies there is something off about the environment, and those messages trigger a larger response. A common characterization of that response is inflammation, which in turn causes an entire cascade of biological responses.
During or before fetal development, a mother can contract an infection and the immune response of the mother can have an impact on the developing fetus. The mother’s immune can trigger a subsequent inflammatory response in the fetus, initiating a cascade of biological responses as a result.
Due to the complexity and prevalence of ASD, much more research should be done to better characterize it and to find possible treatments. Unfortunately, this is easier said than done, largely as a result of the complexity and unknown factors of ASD.
Animal Models
Current rodent models are models of autism, not for autism, meaning current models mimic symptoms of autism, but do not contain the entire picture of the disorder. Therefore, there are several animal models to attempt to cover as much of the disorder as possible. Typically, the models can be grouped into several categories:
Environmentally Induced
This mirrors maternal infection that leads to immune dysregulation. This can be done using chemicals found in the body (such as chemicals used in immune response), or other chemicals known to induce ASD-like symptoms.
Physical Damage
Physical damage or lesions seek to target a specific area of the brain to learn more about which structures in the brain are most vital for the development of ASD. However, when the brain is damaged, it takes measures to heal itself, notably neurons moving to fill the space of the damaged area. This makes it difficult to say for-certain damage to one area caused a specific behavior as presented in autism.
Genetic Modifications
Studying ASD with genetic modifications is very difficult because ASD is not caused by a single gene, but rather many genes functioning and influencing each other. However, by studying other diseases that share ASD pathology and that are impacted by a single gene; scientists can better study the complicated behavioral factors of autism through different diseases. Genetic modifications do not supply a model that presents with the same physical issues present in individuals with ASD, such as neuronal wiring discussed earlier.
There are limitations to any model, but there are large limitations with the available models for autism. State of the art behavioral software recently has been developed to a level that would prove useful for disorders as complicated as ASD, which will aid in the validity of studies, but as mentioned there is not a single model we can rely on to study autism. We must take a holistic approach and try to piece information learned from various models together to get a more complete picture of autism spectrum disorder.
Sources:
https://www.cdc.gov/ncbddd/autism/data.html
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5137861/pdf/fso-01-63.pdf
https://www.ncbi.nlm.nih.gov/pubmed/28499914
