This research paper provides a comprehensive examination of autism spectrum disorder (ASD), covering its history and etiology, objective diagnostic criteria and tools, putative ASD traits, incidence and prevalence rates, theorized genetic and environmental causation, and twin study findings. Drawing on multiple peer-reviewed studies, the paper explores genetic and chromosomal links to autism, compares diagnostic methods such as G-banded karyotyping and chromosomal microarray analysis, and reviews behavioral traits used to characterize ASD across age groups. Twin study concordance rates further support a genetic basis for the disorder, while environmental causation remains inconclusive. The paper underscores that autism is a multifactorial condition requiring continued research.
Autism spectrum disorder (ASD) has traditionally been understood as a distinct behavioral disorder characterized by impairments in social interaction and communication. Autism has also been characterized as a neurodevelopmental disorder (Sbacchi, 2010). Many autistic patients demonstrate behavioral patterns that are sometimes restricted, repetitive, or stereotypical. Such patterns of behavior are marked by language difficulties such as difficulty pronouncing sounds, stumbling on words, or echoing what was said. Also common in autistic individuals is an effect on social ability and social interaction (Steer, 2010).
Throughout this research study, numerous categories relating to autism were examined: the history and etiology (causes) of autism, objective diagnosis criteria, tools and procedures for diagnosing autism, putative traits, incidence and prevalence of autism, theorized genetic causation, twin studies, and theorized environmental causation. Studies discussed in this report were conducted on various samples of autistic patients. For example, to determine putative autistic traits, studies were conducted on children diagnosed with autism ranging from six months to nine years of age, while studies to determine environmental causation were conducted on laboratory animals.
Findings of the research linked autism to genetic and chromosomal disorders, although research linking autism to environmental disorders has been inconclusive. As with most medical conditions, research is still being conducted regarding the causes and incidence of autism. Although studies provide clarity and understanding of many of the causes and traits of autism, much of the research conducted remains inconclusive. As research progresses, this condition will become better understood and treatment options will undoubtedly evolve along with it.
Although autism affects an estimated 1 in every 110 individuals, no consistent causes for the disorder have been identified (Satterfield, 2010). Much research has been performed regarding the causes of autism, and many studies have linked the disorder to genetic disorders involving mutation or deletion of DNA, or to malformation of chromosomes. Environmental factors — such as exposure of the mother to chemicals or preservatives — have also been studied as a contributing factor in autism, although the results in this area are not yet conclusive.
In their study, Satterfield et al. screened for a link between XMRV and autism. XMRV (Xenotropic murine leukemia virus-related virus) is a recently discovered retrovirus that can infect humans (Satterfield, 2010). The results of their study found no association between XMRV and autism (Satterfield, 2010).
Also studied as a potential link to autism is the assessment of plasma cortisol and the adrenocorticotropic hormone (ACTH). The levels of plasma cortisol and ACTH in autistic children and adolescents were studied to address their relationship to the disease. Cortisol plays an important role in proper emotional development and functioning. Abnormal cortisol levels have been found in chronic depression and suicide-prone behaviors, and lower levels of cortisol were found among Holocaust survivors with posttraumatic stress disorder (Hamza, 2010).
The Hamza study revealed significantly lower morning basal cortisol and higher ACTH levels, as well as a lower cortisol response after ACTH stimulation, as autistic severity increased. In other words, as the severity of autism increased, cortisol levels became lower — or abnormal. This pattern is similar to what was observed in Holocaust survivors with posttraumatic stress disorder. The results of this study were confirmed by a separate study (Hamza, 2010).
Additional causes related to genetics, along with more detailed studies addressing the causes of autism, are addressed later in this report. However, as has been demonstrated, there is no single identified cause of the disorder. Each study conducted results in additional understanding, but determination of one primary cause remains out of reach.
Throughout the years, various criteria, research tools, and procedures have been used in attempts to diagnose autism. Dr. David Miller examined the methods of testing for autism and concluded that the discovery of genetic variables contributing to ASD is the first step in developing effective clinical diagnostic genetic tests. He further concluded that most cases are still unexplained by current genetic testing and will require ongoing discovery to improve testing yield (Miller, 2010). Miller suggests that current genetic testing is not yielding results that best explain the causes of autism. As a solution, he proposes that the ideal genetic test would identify genetic susceptibility to autism (Miller, 2010).
To illustrate how genes are evaluated in autism studies, the Traylor study examined six subjects ascertained from different areas of the world. Study subjects 1 and 2 were identified through Genetic Health Services Victoria in Melbourne, Australia, while subjects 3–6 were identified through Signature Genomic Laboratories (Traylor, 2010). Subjects 1 and 2 had Single Nucleotide Polymorphism (SNP) array analysis performed using the 250K-feature Nsp GeneChip according to Affymetrix (Santa Clara, CA) protocols. Genetic deletions in subjects 3–6 were identified by array comparative genomic hybridization (aCGH) using various microarray platforms at Signature Genomic Laboratories (Traylor, 2010). These studies illustrate two methods used to determine gene abnormalities in autistic patients.
Currently, the G-banded karyotype is the first-tier cytogenetic test for patients. This method tests for chromosomal abnormalities and yields a positive result in approximately 2%–3% of patients with autism (Miller, 2010). Miller suggests that this method should be replaced with chromosomal microarray (CMA) as the first-tier cytogenetic test. CMA is a form of array comparative genomic hybridization that detects the vast majority of events identified by karyotype and can also detect many more events that fall below karyotypic resolution. This method yields positive results in 7%–10% of patients with autism (Miller, 2010), making it a significantly stronger method of abnormal chromosomal detection than the G-banded karyotype.
"Describes seven behavioral factors characteristic of ASD"
"Reports ASD prevalence rates from ALSPAC and other studies"
"Examines genetic mutations and inconclusive environmental factors"
"Monozygotic twin concordance supports genetic basis for autism"
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