Autism Spectrum Disorder: A Comprehensive Overview
Learn about ASD, from its Etiology to Neurobiology
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Autism Spectrum Disorder
Autism spectrum disorder is a neurodevelopmental disorder that includes social interaction impairments with limited and repetitive actions (Garrido et al., 2020). In the fifth edition of the DSM (2013), the American Psychiatric Association identifies deficits in communication and social interaction, as well as an inability to initiate or respond to social conversations. These impairments may include limitations in reciprocal non-verbal communication and restricted or repetitive patterns of interest or behavior. The DSM-5 (2013) adds various modifiers to differentiate symptoms of autism spectrum disorder, which can include intellectual impairment, language limitations, and comorbidity with other mental or behavioral conditions. Disorders. In 2013, DSM-5 introduced three severity levels to classify autism spectrum disorder. These levels are based on the degree of support an individual needs to function to the best of their abilities. The severity levels are social communication, restrictive, and repetitive behaviors. Each level describes the deficits mentioned above in terms of their intensity and the level of support required.
Mehling et al. (2016) discuss the inadequacy of past diagnostic manuals in determining the severity levels of developmental disorders. They highlight the lack of targeted research to identify the intensity of severity within an individual. Although the DSM-5 (2013) includes a marker for the level of seriousness, it still lacks objective measures to help parents and professionals accurately estimate support needs, treatment plans, and prognosis. Furthermore, understanding parents'
stress levels can help in considering the needs of typical siblings.
Etiology of Autism Spectrum Disorder
Gyawali et al. (2019) discuss research that shows a significant hereditary factor in the etiology of autism spectrum disorder. Previously, researchers suspected early childhood diseases and vaccines to be considerable contributors to the development of autism spectrum disorders. Autism spectrum disorder is associated with mumps, measles, and rubella. However, as years of research continued, studies did not show a direct connection between thimerosal-containing vaccines and an autism spectrum disorder. Genetic studies and epigenetics define how behaviors and environments can cause deviations in how genes function in the body. Therefore, parental and environmental factors were investigated to understand the involvement in neurobiological changes associated with an autism spectrum disorder. (Gyawali et al.2019).
Hodges et al. (2020) explain that few studies have been conducted on the differences in the neurological structure of people diagnosed with autism spectrum disorder, specifically differences in the construction and connections of the brain. Studies have shown that people with autism spectrum disorders show different brain structures, including the brain’s limbic system, frontal, temporal lobe, and cortical variances.
Hodges et al. (2020) discuss how genetic factors for the expression of autism spectrum disorder have been studied in twin studies. There is a much higher risk factor for individuals diagnosed with an autism spectrum disorder in identical twins. Genes and neurotransmitters documented in people diagnosed with autism spectrum disorder include those that affect neuronal excitability.
Environmental factors contributing to autism spectrum disorder can occur prenatally, perinatally, and postnatally. For example, prenatal exposure to thalidomide and valproic acid has increased the risk for autism spectrum disorder., Advanced maternal and paternal age have been another factor in an increased risk of having a child with an autism spectrum disorder.
Other environmental factors include a maternal history of autoimmune diseases, such as diabetes, thyroid disease, or psoriasis; however, more studies are needed in these areas. In addition, maternal infection or immune stimulation during pregnancy is another area considered a potential risk factor (Hodges et al., 2020)
The Neurobiology of Autism Spectrum Disorder
Studies of the structure and function of the neurobiology of autism spectrum disorder have been done through MRI, neuroimaging, and autopsies. Lukito et al. (2020) report that some of the latest studies on autistic brains seem to detect an association between smaller brain cells and increased density. Lukito et al. (2020) state that certain brain parts have this configuration. The brain areas with a high density of smaller cells in people with an autism spectrum disorder include the hippocampus, limbic system, and amygdala. Neurologically, young people with autism spectrum disorder presented with enlarged neurons in the cerebellar nuclei, inferior olive, and vertical limb of the diagonal band of broca18. Added research discussed the prefrontal cortex. Lukito et al. (2020) comment that the differences in autism spectrum brains imply a pattern of limited brain development.
Hashem et al. (2021) conducted a review article on the genetics and structure of the autism spectrum brain, which showed that smaller cell size and increased cell density in the hippocampus, limbic system, entorhinal cortex, and amygdala have been observed in people with autism spectrum disorders. In addition, Hashem et al. (2021) continued to discuss that children with autism showed enlarged neurons in the cerebellar nuclei, inferior olive, and vertical limb of the diagonal band of broca18. Petit et al. (2021) investigated brain changes in autism spectrum disorder and used magnetic resonance imaging to identify differences in brain structure and function. MRI findings in children with an autism spectrum disorder from 2 to 5 years old uncovered an atypical frontal and temporal lobes development, reduced gray matter, decreased white matter, and an increased amygdala volume compared to same-age typical children. In addition to amygdala enlargement, young children with autism showed increased cerebral volume.
Imaging studies have seen decreased and increased cortical thickness in patients with an autism spectrum disorder. There has been no research that has uncovered one ‘characteristic’ brain structure for autism. Studies of brain structure often yield different results — there is significant variation across individuals. However, some tendencies have appeared in some groups of autistic people. Shen et al. (2013) note that people with autism spectrum disorder have decreased amounts of brain tissue in the cerebellum and the corpus callosum. The cerebellum plays a role in cognition and interactive skills. People who lack all or part of one white matter tract, the corpus callosum, which connects the two hemispheres of the brain, have an increased likelihood of being autistic or having traits of autism spectrum disorder. The corpus callosum has many long-range connections that extend throughout the brain; disrupting those connections may lead to autism traits, supporting the connectivity theory of autism. Shen et al. (2013) explained that infants diagnosed with autism spectrum disorder have enlarged heads and brains in infancy and childhood. Then they start to shrink prematurely, before their mid-twenties.
Yankowitz et al. (2021), in a review of recent literature, found that abnormalities in brain volume for children with autism spectrum disorder are common. Brain overgrowth is related to cortical thickness, and the bundles of long nerve fiber connections that connect brain regions are distorted in people with autism. Researchers typically gather data about the structure of white matter using diffusion MRI, which measures the flow of water throughout the brain. Karahan et al. (2018) summarize the main differences in the brains of people with an autism spectrum disorder using diffusion imaging of people’s distorted white matter region development from ages 8 to 25. The regions with malformed bundles of fibers in the white matter display disorganized neural communication. Disrupted neural communications can correlate with cognitive, social, and emotional functions.
Meaner, Shaw, et al. (2020) evaluated data from the Early Autism and Developmental Disabilities Monitoring Network group of programs funded by the CDC to estimate the number of children with autism spectrum disorders and other developmental disabilities.
Autism Spectrum Disorder
Autism spectrum disorder is a neurodevelopmental disorder that includes social interaction impairments with limited and repetitive actions (Garrido et al., 2020). In the fifth edition of the DSM (2013), the American Psychiatric Association identifies deficits in communication and social interaction, as well as an inability to initiate or respond to social conversations. These impairments may include limitations in reciprocal non-verbal communication and restricted or repetitive patterns of interest or behavior. The DSM-5 (2013) adds various modifiers to differentiate symptoms of autism spectrum disorder, which can include intellectual impairment, language limitations, and comorbidity with other mental or behavioral conditions. Disorders. In 2013, DSM-5 introduced three severity levels to classify autism spectrum disorder. These levels are based on the degree of support an individual needs to function to the best of their abilities. The severity levels are social communication, restrictive, and repetitive behaviors. Each level describes the deficits mentioned above in terms of their intensity and the level of support required.
Mehling et al. (2016) discuss the inadequacy of past diagnostic manuals in determining the severity levels of developmental disorders. They highlight the lack of targeted research to identify the intensity of severity within an individual. Although the DSM-5 (2013) includes a marker for the level of seriousness, it still lacks objective measures to help parents and professionals accurately estimate support needs, treatment plans, and prognosis. Furthermore, understanding parents' stress levels can help in considering the needs of typical siblings.
Etiology of Autism Spectrum Disorder
Gyawali et al. (2019) discuss research showing a significant heredity factor in the etiology of autism spectrum disorder. Previously, researchers suspected early childhood diseases and vaccines to be considerable contributors to the development of autism spectrum disorders. Autism spectrum disorder is associated with mumps, measles, and rubella. However, as years of research continued, studies did not show a direct connection between thimerosal-containing vaccines and an autism spectrum disorder. Genetic studies and epigenetics define how behaviors and environments can cause deviations in how genes function in the body. Therefore, parental and environmental factors were investigated to understand the involvement in neurobiological changes associated with an autism spectrum disorder. (Gyawali et al.2019).
Hodges et al. (2020) explain that few studies have been conducted on the differences in the neurological structure of people diagnosed with autism spectrum disorder, specifically differences in the construction and connections of the brain. Studies have shown that people with autism spectrum disorders show different brain structures, including the brain’s limbic system, frontal, temporal lobe, and cortical variances.
Hodges et al. (2020) discuss how genetic factors for the expression of autism spectrum disorder have been studied in twin studies. There is a much higher risk factor for individuals diagnosed with an autism spectrum disorder in identical twins. Genes and neurotransmitters documented in people diagnosed with autism spectrum disorder include those that affect neuronal excitability.
Environmental factors contributing to autism spectrum disorder can occur prenatally, perinatally, and postnatally. For example, prenatal exposure to thalidomide and valproic acid has increased the risk for autism spectrum disorder., Advanced maternal and paternal age have been another factor in an increased risk of having a child with an autism spectrum disorder.
Other environmental factors include a maternal history of autoimmune diseases, such as diabetes, thyroid disease, or psoriasis; however, more studies are needed in these areas. In addition, maternal infection or immune stimulation during pregnancy is another area considered a potential risk factor (Hodges et al., 2020)
The Neurobiology of Autism Spectrum Disorder
Studies of the structure and function of the neurobiology of autism spectrum disorder have been done through MRI, neuroimaging, and autopsies. Lukito et al. (2020) report that some of the latest studies on autistic brains seem to detect an association between smaller brain cells and increased density. Lukito et al. (2020) state that certain brain parts have this configuration. The brain areas with a high density of smaller cells in people with an autism spectrum disorder include the hippocampus, limbic system, and amygdala. Neurologically, young people with autism spectrum disorder presented with enlarged neurons in the cerebellar nuclei, inferior olive, and vertical limb of the diagonal band of broca18. Added research discussed the prefrontal cortex. Lukito et al. (2020) comment that the differences in autism spectrum brains imply a pattern of limited brain development.
Hashem et al. (2021) conducted a review article on the genetics and structure of the autism spectrum brain, which showed that smaller cell size and increased cell density in the hippocampus, limbic system, entorhinal cortex, and amygdala have been observed in people with autism spectrum disorders. In addition, Hashem et al. (2021) continued to discuss that children with autism showed enlarged neurons in the cerebellar nuclei, inferior olive, and vertical limb of the diagonal band of broca18. Petit et al. (2021) investigated brain changes in autism spectrum disorder and used magnetic resonance imaging to identify differences in brain structure and function. MRI findings in children with an autism spectrum disorder from 2 to 5 years old uncovered an atypical frontal and temporal lobes development, reduced gray matter, decreased white matter, and an increased amygdala volume compared to same-age typical children. In addition to amygdala enlargement, young children with autism showed increased cerebral volume.
Imaging studies have seen decreased and increased cortical thickness in patients with an autism spectrum disorder. There has been no research that has uncovered one ‘characteristic’ brain structure for autism. Studies of brain structure often yield different results — there is significant variation across individuals. However, some tendencies have appeared in some groups of autistic people. Shen et al. (2013) note that people with autism spectrum disorder have decreased amounts of brain tissue in the cerebellum and the corpus callosum. The cerebellum plays a role in cognition and interactive skills. People who lack all or part of one white matter tract, the corpus callosum, which connects the two hemispheres of the brain, have an increased likelihood of being autistic or having traits of autism spectrum disorder. The corpus callosum has many long-range connections that extend throughout the brain; disrupting those connections may lead to autism traits, supporting the connectivity theory of autism. Shen et al. (2013) explained that infants diagnosed with autism spectrum disorder have enlarged heads and brains in infancy and childhood. Then they start to shrink prematurely, before their mid-twenties.
Yankowitz et al. (2021), in a review of recent literature, found that abnormalities in brain volume for children with autism spectrum disorder are common. Brain overgrowth is related to cortical thickness, and the bundles of long nerve fiber connections that connect brain regions are distorted in people with autism. Researchers typically gather data about the structure of white matter using diffusion MRI, which measures the flow of water throughout the brain. Karahan et al. (2018) summarize the main differences in the brains of people with an autism spectrum disorder using diffusion imaging of people’s distorted white matter region development from ages 8 to 25. The regions with malformed bundles of fibers in the white matter display disorganized neural communication. Disrupted neural communications can correlate with cognitive, social, and emotional functions.
Meaner, Shaw, et al. (2020) evaluated data from the Early Autism and Developmental Disabilities Monitoring Network group of programs funded by the CDC to estimate the number of children with autism spectrum disorders and other developmental disabilities.
References
References are part of a larger paper, and they can be made available.