Abstract
Autism Spectrum Disorder (ASD) is becoming increasingly prevalent amongst individuals today. The reason for this could be that clinicians are either substantially improving diagnostic methods or autism is becoming more common due to various contributing factors. Furthermore, in addition to the specific screenings and evaluations that are used to identify autism, researchers are developing more and more tests that serve as useful tools for diagnostics. This study compiles several different factors linked to autism, addresses some theories regarding the modern rise of autism, and explains the current ASD diagnosis process and new diagnostic methods. The contributing factors explained in this study include genetics, specific genes, the environment, biological factors, neurological factors, the gut microbiome, and more. Considering that there is a significant number of causes of autism and currently a multitude of conjectures regarding what is truly linked to autism, this paper attempts to accumulate all available data in an organised manner and present the most relevant conclusions.
Introduction
Dr. Stephen Shore, a special education professor at Adelphi University, once said, “If you’ve met one person with autism, you’ve met one person with autism.” In other words, individuals on the spectrum each have different strengths and weaknesses. Some may find it more challenging to communicate and interact with others while others may experience little difficulty when having a conversation.
According to the latest CDC report, in twenty years, autism went from being identified in one out of one hundred fifty children to being identified in one out of thirty-six children (CDC). Autism Spectrum Disorder (ASD) is a developmental disability that results in social interaction impairments, communication difficulties, repetitive behaviors, and obsessive interests. Some common social interaction impairments include the lack of communication, eye contact, body posture, and facial expressions, which can lead to individuals on the spectrum struggling to develop relationships. In addition, some communication impairments are the repetitive use of the same language and the inability to initiate conversations, which suggests a lack of speech development. Lastly, some repetitive behaviors and interests include intense focus and preoccupation with certain parts of objects, recurrent body movements, and extreme inflexibility to changes to routine (Saringer).
Levels of Autism
Essentially, there are three levels of autism, which vary from mild to severe based on their behavior, their social skills, and how much support they need. To start, ASD level 1 is the lowest classification and these individuals need some support due to their lack of social interaction and organization skills. Next, those with ASD level 2 require a considerable amount of support; these individuals struggle to communicate verbally and possess repetitive behaviors and strong interests in particular subjects. Lastly, ASD level 3 is the most severe level, where individuals require significantly more support than individuals with ASD level 1 or 2. In addition to having more extreme characteristics than those with ASD level 1 or 2, they ultimately experience more trouble communicating, displaying very limited social skills (Lane Regional Medical Center).
Main Causes of Autism
Current research shows that there are several different factors that lead to the development of autism.
Genetics
To begin, a huge contributing factor to ASD is genetics. Likewise, according to Saringer, “having a sibling with autism raises children’s odds of being diagnosed as well — likely due to similar genetic backgrounds.” Additionally, genetic disorders, including Rett syndrome, fragile X syndrome, and tuberous sclerosis are suspected to contribute to the likelihood of developing autism. In Rett syndrome, there is evidence that suggests that high brain deterioration may lead to autism (Saringer). In addition, mutations in the FMR1 gene on the X chromosomes prevent gene expression and cause fragile X syndrome. As a result, the FMR1 protein being absent during brain development excites the neurons that are associated with the syndrome (Rura). Consequently, the overexcitement of the neurons from Fragile X syndrome is another factor that researchers believe contributes to the development of autism. Lastly, according to Saringer, “the TSC gene mutation found in tuberous sclerosis can cause autism if it occurs during critical junctures in brain development.” In summary, researchers state that the genetic mutations found in these three genetic disorders often cause the development of ASD. Other genetic disorders that can increase the risk for ASD include phenylketonuria, chromosome problems, and neurofibromatosis. In addition, a genetic mutation of the MTHFR gene impeded the process of methylation. As a result, an essential antioxidant for the body called glutathione is produced less efficiently and effectively, which causes oxidative stress. Scientists believe that this mutation is a risk factor for autism. As stated by Saringer, “These are environmental factors, but it’s believed that genetic factors make these problems more likely.” Ultimately, if someone has a certain genetic mutation in one of their genes that may contribute to being diagnosed with autism, specific environmental conditions or circumstances may increase the likelihood of developing autism.
Likewise, there are more than one hundred genes on different chromosomes that contribute to the development of ASD and many people with autism have mutations in these genes. According to NIH, “most people with autism have different mutations and combinations of mutations,” and not all people with autism have “changes in every gene that scientists have linked to ASD. Many people without autism or autism symptoms also have some of these genetic mutations that scientists have linked to autism.” Therefore, specific combinations of mutations or mutations alone may cause symptoms of autism and control how severe those symptoms are. In other words, different genetic mutations may increase the likelihood of being diagnosed with autism. Ultimately, by being susceptible to ASD due to genetic mutations, environmental factors might result in the development of autism (NIH).
Moreover, epigenetics is the study of how one’s behaviors and the environment can lead to changes that affect the way their genes work. Epigenetic changes do not change DNA sequences but they change how they are expressed (Centers for Disease Control and Prevention). Ultimately, epigenetic changes in the womb can cause autism. As of now, the epigenetic changes linked to autism include maternal influenza infection, prolonged maternal fever, and maternal asthma during pregnancy, which implies that pregnancy is a critical period when brain development can be affected (Saringer).
Specific Genes
Additionally, research has shown that there are several genes that are involved in the development of autism. According to Mccall, “Six of these are called ubiquitin ligases and they're responsible for attaching molecular tags called ubiquitins to proteins.” Likewise, some scientists believe that a huge factor that causes autism is a gene mutation that inhibits the proper function of an ubiquitin ligase. At Washington University, a few scientists tested this hypothesis. They used young mice and removed an ubiquitin gene called RNF8 in neurons in the cerebellum, which is a specific area of the brain that is affected by autism and plays an important role in language, movement, and attention. As a result, the mice that were missing the gene developed 50% more synapses than the mice that had the RNF8 gene, which ultimately impacted their ability to learn. Moreover, the researchers “trained the mice to associate a puff of air to the eye with a blinking light” in order to see if the mice without the RNF8 gene had lower motor skills. Overall, although a human with autism isn’t the exact same as a mouse that doesn’t shut its eyes when trained to, this study highlights an association between behavior and synapses (Mccall).
Furthermore, one recent investigation looked at the DNA of more than 35,584 people worldwide, which included 11,986 autistic individuals. Subsequently, the scientists identified variants in 102 genes that were linked with an increased probability of developing autism. In addition, 53 of the genes identified were predominantly associated with autism and not another developmental condition. As a means of expanding their research, the researchers discovered that autistic people with those specific gene variants associated with autism were more intelligent and quick-witted than individuals on the spectrum who do not have these variants. Likewise, the gene variants were in the cerebral cortex, which is the part of your brain that is responsible for complex behaviors. Ultimately, these variants play a huge role in how brain neurons function and connect with one another. Similarly, the gene variants also play a role in gene regulation, turning other genes on or off. A certain pathway that is triggered or inhibited by these variants could result in the development of autism (Drake).
The Environment
Additionally, many scientists theorize that chemicals from the environment interact with the central nervous system which ultimately causes autism. To start, it has been proven that heavy metals, such as lead, cadmium, arsenic, and mercury, have been linked to ASD. Pesticides and insecticides may be another cause of autism. According to the published study titled, “Prenatal and infant exposure to ambient pesticides and autism spectrum disorder in children: population based case-control study,” pesticide exposure was linked with autism spectrum disorder, suggesting the fact that specific pesticides were able to alter gene expression and have neurobehavioral effects (Ehrenstein). Finally, exposure to neurotoxicants at a young age has also been associated with the development of autism.
Moreover, according to Saringer, “early exposure to an unpredictable environment and too much exposure to screen time in the developmental years may cause autism.”
Biological Factors
According to Miller, research has proven that several problems regarding “brain connectivity, growth or overgrowth in certain areas of the brain, and metabolism (how the body produces energy)” have been linked to the development of autism.
In addition, there has been some research that connects problems in the body’s immune system, which protects against infections, with autism. These problems include the functionality of the immune system, inflammation, and the creation of antibodies to a condition that the body isn’t used to. As said earlier, infections during pregnancy “could increase the child’s likelihood of having autism,” (Miller).
Additionally, scientists have recently discovered a connection between autism and mitochondrial function (Miller). Mitochondria creates most of the energy for the cell, generating ATP through oxidative phosphorylation. As stated by Miller, “Scientists suggest that mitochondria are also affected by some of the same environmental factors that can increase the chances of someone being diagnosed with autism.”
Neurological Factors
According to Drake, current research suggests a connection between certain types of cell malfunctions and autism. At the Lieber Institute for Brain Development in Baltimore, MD, a group of scientists noticed “a decrease in the integrity of myelin, a protective sheath surrounding nerve cells in the brain, in mice with a syndromic form of autism” (Drake). As a result, the results of their investigation showed that there was a “gene variant-based malfunction” in certain cells that produce myelin called oligodendrocytes. In their study, which was published in Nature Neuroscience, they determined that this malfunction could result in limited myelin production in the nerve cells and possibly disrupt communication between nerves in the brain. With mouse models, more investigations are happening that consist of treatments that could increase the myelination in the brain in order to see whether it improves the behaviors that individuals with autism struggle with (Drake).
The Gut Microbiome
Another considerable factor that researchers are taking into account is the gastrointestinal (gut) microbiome. According to Drake, multiple studies have shown a connection between autism and imbalances in the gut microbiome. In addition, several studies have proved that stabilizing the populations of gut microbes can work towards improving some of the disadvantageous behaviors that autistic individuals have. One particular study published in the journal Microbiome in 2017 focussed on Microbiota Transfer Therapy (MTT) in autistic children. After the MTT treatment, not only was there a decrease in gastrointestinal symptoms, but the individuals also experienced more gut bacterial diversity, and displayed improved language, social interaction, and behavioral symptoms. In a follow-up investigation, researchers found that those who received the MTT treatment had fewer gastrointestinal issues and ultimately continued to show improvement in symptoms related to autism. Furthermore, in a recent study, researchers discovered that mice that lack a gene related to autism called CNTNAP2 have a population of microbes in their intestines and show “some social behaviors similar to those seen in some autistic people.” After the mice were treated with a common strain of gut bacteria that is found in wild-type mice and a common bacterium missing from the microbiome called Lactobacillus reuteri, the social behaviors of the mice improved drastically. Ultimately, this study suggests a link between the gut microbiome and genes (Drake).
Other Factors
Furthermore, it is proven that older parents are more likely to have children with autism. Additionally, having an immediate family member who has autism increases the risk of developing it. Another risk factor for autism is if “the frontal cortex of the baby’s brain overgrows shortly after birth” (Miller).
According to Autism Speaks, boys are four times more likely than girls to have autism. As stated by Morrison, “It takes fewer variants to predispose a boy to developing autism than it does a girl. That is, girls may be spared autism even though they have the same number and kinds of genetic variants that cause the condition in boys.”
The health of the mother is another factor that is being considered when it comes to the causes of autism. According to Saringer, “the odds of an autism diagnosis increase nearly 50% if the mother has been diagnosed with a mental health condition.” In addition, vitamin D deficiency in the mother has been linked to autism spectrum disorder, as well as the intake of folic acid. Likewise, according to Cherney and Seladi-Schulman, some other risk factors for ASD include “low birth weight, metabolic imbalances, a maternal history of viral infections, and fetal exposure to the medications valproic acid or thalidomide.”
Lastly, Miller indicates that it is more likely for a child to be diagnosed with autism if during pregnancy the mother had hypertension or diabetes, experienced an antepartum hemorrhage in the third trimester or postpartum hemorrhage, or had preeclampsia. According to Sarris, “Several studies found that pregnant women with diabetes – including the temporary kind – had a higher risk of delivering a child with autism than mothers who weren't diabetic.” Additionally, hemorrhage during pregnancy is heavy bleeding, and several sources, including NCBI, indicate that hemorrhage is a factor that causes autism. According to marchofdimes.org, preeclampsia causes high blood pressure and causes organs to malfunction. As stated by NCBI, “Preeclampsia can increase risk for developing autistic disorders.”
Vaccines
One important thing to note is that vaccines have been proven to not cause autism. In 1998, in the British medical journal, called Lancet, a study stated that not only do measles and mumps cause autism, but the rubella (MMR) vaccine causes autism as well. Eventually, the study was proven to be false and was retracted (Miller).
How Autism is Currently Diagnosed
Specific screenings and evaluations are used to diagnose autism. According to Miller, clinicians who are diagnosing ASD generally look for “difficulty with back-and-forth conversation, differences in nonverbal communication like facial expressions or body language, and difficulty adjusting behavior to different social settings.”
Additionally, developmental screening for autism consists of various questions that determine whether the child has autism by comparing their behavior to other children of the same age (Cleveland Clinic). One development questionnaire, mentioned by Cherney and Seladi-Schulman, is called Autism Diagnostic Observation Schedule, Second Edition (ADOS-2). When screening for autism, a doctor may look at specific behavioral patterns including specific movements, obsessive interests, attachment to routine, and differences in sensory processing (Miller). It’s important to note that screenings don’t always identify autism in a child. According to Cherney and Seladi-Schulman, “The American Academy of Pediatrics (AAP) recommends that all children undergo ASD screening at ages 18 and 24 months,” because they help to identify ASD in children at a young age. A common screening tool is called The Modified Checklist for Autism in Toddlers (M-CHAT), which consists of a 23-question survey (Cherney and Seladi-Schulman).
Other tests that may be used to identify autism in an individual include DNA testing for genetic diseases, visual and audio tests to rule out any issues with vision and hearing that aren’t related to ASD, and occupational therapy screening (Cherney and Seladi-Schulman).
In addition, another test that is helpful for diagnosing autism is a neuropsychological evaluation, which looks at the history of the child’s behavior, in addition to “cognitive and achievement testing, as well as further specialized testing of memory, attention, and executive function, to pinpoint a child’s abilities and deficits in learning and communicating” (NYULangone).
Lastly, a formal evaluation for autism takes an in-depth look at the child’s behavior and “gives them a structured autism spectrum test” (Cleveland Clinic). Ultimately, these evaluations determine specific strengths and challenges for the person, which is, in essence, a formal diagnosis.
New Diagnostics
To start, according to Baumer and Frueh Health, the FDA approved a new tool that helps to diagnose autism in children. The evaluation consists of a questionnaire answered by the parents, short videos of the child eating and/or playing, and lastly, a questionnaire answered by the medical providers. As described by Baumer and Frueh, “an algorithm compiles the information gathered from those three sections and provides a result of either ‘ASD,’ ‘no ASD,’ or ‘indeterminate.’”
In addition, “the U.S. Food and Drug Administration (FDA) has granted ‘breakthrough device’ designation to a hair-based test designed to aid autism diagnosis,” according to Dattaro. The hair-based test is called StrandDx. In essence, by examining a strand of a child’s hair, the test is able to determine the levels of chemicals in the strand, which captures “a snapshot of [their] ‘exposome’ — some of [their] cumulative environmental exposures and how [they] regulate certain essential nutrients” (Dattaro).
Moreover, the FDA has also approved an app from Cognoa which diagnoses ASD by examining videos of kids communicating with others and doing tasks in addition to analyzing reports from doctors and caregivers (Park).
Another fascinating app that Cognoa has created uses AI to diagnose autism in children and FDA has cleared it. According to Park, “the EarliPoint Evaluation uses eye-tracking technology to monitor a child’s focus and responsiveness while viewing short videos of social interactions between other kids.” In essence, artificial intelligence is able to study the eye movements of the child and draw conclusions from the results by comparing them to reference points based on the child’s age. As a result, if AI observes any substantial differences, it concludes that the child’s social, verbal, and even non-verbal abilities aren’t close to the standard for their age, which suggests that they have autism (Park).
Furthermore, another test for ASD uses blood and urine to determine autism. Although many are skeptical about it, according to Enzo, it “could lead to earlier diagnosis and intervention and potentially identify new causes of ASD.” Essentially, researchers took blood and urine samples from fasting children and were able to test for markers of oxidation, nitration, and protein glycation. As stated by Enzo, “Modified protein damaged by metabolic processes including oxidation and glycation were evaluated and used to predict ASD (…) Changes in the plasma AGEs likely suggest dysfunctional metabolism and reduced renal clearance that could enable high sensitivity detection and diagnosis specificity for ASD.” Researchers at the University of Warwick executed practically the same experiment. They found a link between damage to proteins in the blood’s plasma and autism. Their most accurate blood and urine test concluded that children on the spectrum had higher levels of dityrosine and advanced glycation end-products (AGEs) (Sandoiu). According to Sandoiu, “Dityrosine is a marker of oxidation damage, and AGEs are the result of glycation,” a process where sugars combine with amino acids. Ultimately, this test was 92% accurate.
Conclusion
Essentially, there are several different factors, including genetic, environmental, biological, neurological, and more, that result in the development of autism. Not only are the combination of various factors that cause autism interesting but also the fact that there is a spectrum and every autistic individual is different from one another is extremely fascinating. In essence, every single child with autism is unique and special in their own way. Therefore, autism is completely different from other disabilities due to the fact that it is a spectrum disorder. Ultimately, autism affects people in completely different ways. Autistic individuals vary in their abilities, strengths, and challenges, which ultimately sets autism apart from any other developmental disorder. The Centers for Disease Control and Prevention (CDC) states that the rate of autism diagnosis is higher than ever before (Ries). This accentuates the fact that we must grow awareness of ASD so that it can start to be diagnosed in children early on in order for them to get the support they need right away. In conclusion, the beauty of autism is that people on the spectrum are authentic and entirely themselves. Dr. Temple Grandin, a professor with autism, once said, “I am different, not less.” I believe our world can learn a lot from this quote.
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