Diagnoses of autism have become more frequent since the 1980s, which has led to various controversies about both the cause of autism and the nature of the diagnoses themselves. Whether autism has mainly a genetic or developmental cause, and the degree of coincidence between autism and intellectual disability, are all matters of current scientific controversy as well as inquiry. There is also more sociopolitical debate as to whether autism should be considered a disability on its own.
Most recent reviews of epidemiology estimate a prevalence of one to two cases per 1,000 people for autism, and about six per 1,000 for autism spectrum disorder (ASD); because of inadequate data, these numbers may underestimate the true prevalence of ASD. ASD averages a 4.3:1 male-to-female ratio. The number of children on the autism spectrum has increased dramatically since the 1980s, at least partly due to changes in diagnostic practice; it is unclear whether prevalence has actually increased; and as-yet-unidentified environmental risk factors cannot be ruled out. The risk of autism is associated with several prenatal factors, including advanced parental age and diabetes in the mother during pregnancy. ASD is associated with several genetic disorders and epilepsy. Autism is also associated with intellectual disability.
The role of genetic influence on ASD has been heavily researched over the past few years. ASD is considered to have polygenic traits since there is not a single risk factor, but multiple ones.
Multiple twin and family studies have been conducted in order to observe any genetic influence in diagnosing ASD. The chance of both twins having ASD was significantly higher in identical twins than fraternal twins, concluding that ASD is heritable. A reoccurring finding is that de novo (new mutation) copy number variants are a primary cause of ASD - they alter synaptic functions; germ line mutations can produce de novo CNVs. These mutations can only be passed on to offspring; this explains the phenomenon that occurs when the child has symptoms of ASD, but the parents have no symptoms or history of ASD. De novo variants differ from person to person, i.e one variant can cause ASD in one person, whereas another person would need multiple variants to cause the same disorder. Loss of function variants occur in 16-18% of ASD diagnoses, which is nearly double the normal population. These loss of function variants reduce function in the protein neurexin, which connects neurons at the synapse and is important for neurological development; deletion mutations of neurexin are also very common in people with autism, as well as other neurological disorders like schizophrenia, bipolar disorder, and ADHD.
Gut microbiome has a relation to ASD. Excessive Clostridia spp. was found in children with ASD and gastrointestinal difficulties; Clostridia spp produces propionic acid, which is impaired or in excess in people with ASD Specifically, C. tetani and C. histolyticum are two species of this bacteria that affect people with ASD. C. tetani produces tetanus neurotoxin in the intestinal tract; C. histolyticum is a toxin producer that is abundant in people diagnosed with ASD. Both of these could contribute to neurological symptoms.
The idea of a link between vaccines and autism was extensively investigated and shown to be false. The scientific consensus is that there is no relationship, causal or otherwise, between vaccines and incidence of autism, and vaccine ingredients do not cause autism.
Nevertheless, the anti-vaccination movement continues to promote myths, conspiracy theories and misinformation linking the two. A developing tactic appears to be the "promotion of irrelevant research [as] an active aggregation of several questionable or peripherally related research studies in an attempt to justify the science underlying a questionable claim."
The percentage of autistic individuals who also meet criteria for intellectual disability has been reported as anywhere from 25% to 70%, a wide variation illustrating the difficulty of assessing autistic intelligence. For pervasive developmental disorder not otherwise specified (PDD-NOS), the association with intellectual disability is much weaker. The diagnosis of Asperger syndrome excludes clinically significant delays in mental or cognitive skills.
A 2007 study suggested that Raven's Progressive Matrices (RPM), a test of abstract reasoning, may be a better indicator of intelligence for autistic children than the more commonly used Wechsler Intelligence Scale for Children (WISC). Researchers suspected that the WISC relied too heavily on language to be an accurate measure of intelligence for autistic individuals. Their study revealed that the neurotypical children scored similarly on both tests, but the autistic children fared far better on the RPM than on the WISC. The RPM measures abstract, general and fluid reasoning, an ability autistic individuals have been presumed to lack. A 2008 study found a similar effect, but to a much lesser degree and only for individuals with IQs less than 85 on the Wechsler scales.
Facilitated communication is a scientifically discredited technique that attempts to facilitate communication by people with severe educational and communication disabilities. The facilitator holds or gently touches the disabled person's arm or hand during this process and attempts to help them move to type on a special keyboard. It was used by many hopeful parents of individuals with autism when it was first introduced during the early 1990s by Douglas Biklen, a professor at Syracuse University.
There is widespread agreement within the scientific community and multiple disability advocacy organizations that FC is not a valid technique for authentically augmenting the communication skills of those with autism spectrum disorder. Instead, research indicates that the facilitator is the source of the messages obtained through FC (involving ideomotor effect guidance of the arm of the patient by the facilitator). Thus, studies have consistently found that patients are unable to provide the correct response to even simple questions when the facilitator does not know the answers to the questions (e.g., showing the patient but not the facilitator an object). In addition, numerous cases have been reported by investigators in which disabled persons were assumed by facilitators to be typing a coherent message while the patient's eyes were closed or while they were looking away from or showing no particular interest in the letter board. Despite the evidence opposing FC, many continue to use and promote this technique.
Note that facilitated communication is separate and different from a range of scientifically-supported augmentative and alternative communication (AAC) devices and processes that facilitate communication for people with communication difficulties.
There are two major conceptualizations of autism within autism advocacy. Those who favour the pathology paradigm, which aligns with the medical model of disability, see autism as a disorder to be treated or cured. Those who favor the pathology paradigm argue that atypical behaviors of autistic individuals are detrimental and should therefore be reduced or eliminated through behavior modification therapies. Their advocacy efforts focus primarily on medical research to identify genetic and environmental risk factors in autism. Those who favour the neurodiversity paradigm, which aligns with the social model of disability, see autism as a naturally-occurring variation in the brain. Neurodiversity advocates argue that efforts to eliminate autism should not be compared, for example, to curing cancer, but instead to the antiquated notion of curing left-handedness. Their advocacy efforts focus primarily on acceptance, accommodation, and support for autistic people as "neuro-minorities" in society. These two paradigms are not fully exclusive, and many people hold a combination of these viewpoints.
The pathology paradigm is the traditional view of autism through a biomedical lens, in which it is seen as a disorder characterized by various impairments, mainly in communication and social interaction. Those taking this perspective believe that autism is generally a kind of harmful dysfunction. Ways of functioning which diverge from a typical brain are "incorrect" or "unhealthy" and must therefore be treated or cured. The atypical behaviors of autistic individuals are considered a detriment to social and professional success and should therefore be reduced or eliminated through therapy.
Advocates with this view include both a small but significant minority of autistic adults and large majority of parents of autistic children, but contain a higher percentage of parents when compared to those adopting the neurodiversity paradigm. These advocates believe that medical research is necessary to address the "autism epidemic", reduce suffering, and provide the best outcomes for autistic individuals. In addition to etiological research, other areas of focus may include biology, diagnosis, and treatment, including medication, behavioural and psychological interventions, and the treatment of co-existing medical conditions.
Advocacy groups that focus primarily on medical research include Autism Speaks, the Autism Science Foundation, and its predecessor organizations, the Autism Coalition for Research and Education, the National Alliance for Autism Research, and Cure Autism Now, and the former Autism Research Institute.
The neurodiversity paradigm is a view of autism as a different way of being rather than as a disease or disorder that must be cured. Autistic people are considered to have neurocognitive differences which give them distinct strengths and weaknesses, and are capable of succeeding when appropriately accommodated and supported. Efforts to eliminate autism should not be compared, for example, to curing cancer but instead to the antiquated notion of curing left-handedness.
There is no leader of the neurodiversity movement and little academic research has been conducted on it as a social phenomenon. As such, proponents of the neurodiversity paradigm have heterogenous beliefs, but are consistent in the view that autism cannot be separated from an autistic person. Advocacy efforts may include opposition to therapies that aim to make children "indistinguishable from their peers," accommodations in schools and work environments, and lobbying for the inclusion of autistic people when making decisions that affect them.
Neurodiversity advocates are opposed to medical research for a cure, believing that it will lead to eugenics, and instead support research that helps autistic people thrive as they are. For example, NeuroTribes author Steve Silberman noted a lack of research in regards to seizure-controlling drugs and autistic brains; that sensory differences in autistic people were unheard of until Temple Grandin spoke about her experiences; and that only a small percentage of research funding goes towards the needs of autistic adults.
Advocacy groups that focus primarily on acceptance and accommodation include Autism Network International, Autism National Committee, Autistic Self Advocacy Network, and Autistic Women & Nonbinary Network.
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Although the 2013 fifth revision of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) has more specificity, it also has reports of more limited sensitivity. Owing to the changes to the DSM and the lessening of sensitivity, there is the possibility that individuals who were diagnosed with autistic spectrum disorders (ASD) using the fourth revision (DSM-IV-TR) will not receive the same diagnosis with the DSM-5.
From the 933 individuals that were evaluated, 39 percent of the samples that were diagnosed with an ASD using the DSM-IV-TR criteria did not meet the DSM-5 criteria for that disorder.[unreliable medical source?] Essentially, the DSM-5 criteria no longer classified them with having ASD, deeming them without a diagnosis. It was likely that individuals that exhibited higher cognitive functioning and had other disorders, such as Asperger's or PDD-NOS, were completely excluded from the criteria. Also, it is more probable that younger children who do not exhibit the entirety of the symptoms and characteristics of ASD are more at risk of being excluded by the new criteria since they could have Asperger's, as Asperger's does not usually show symptoms until later in childhood. Because the onset age is different in Asperger's from autism, grouping together the disorders does not typically allow or distinguish the differentiating ages of onset, which is problematic in diagnosing. It is evident, through the various studies, that the number of people being diagnosed will be significantly diminished as well, which is prominently due to the DSM-5's new criteria.