Fact sheet on diagnosis of Autism, an Autism Spectrum Disorder


The causes and etiology of autism, along with other Autism Spectrum Disorders, is an area of debate and controversy. A genetic basis for autism has definitely been established and at this stage it appears that multiple genes may be responsible. There is currently no genetic test that can be done to detect autism.


There is much much research and discussion on possible environmental causes that could affect brain development, and many researchers believe that the causes of Autism Spectrum Disorders will prove to be an interplay of genes and environmental causes. It is theorized that these multiple “causes” interact with each other in subtle and complex ways, and would thus explain the wide range of differing outcomes and behaviors in each individual.


Autism Spectrum Disorders are not caused by emotional deprivation or the way a person has been brought up. Theories such as the "refrigerator mother" have long been discredited.


Genetic cause of autism

Scientists generally agree that there is at least a genetic basis for autism, although this may still be debated by some psychology researchers, parents of children diagnosed with autism, and members of the autistic community. Many researchers suspect that autism results from genetically mediated vulnerabilities to environmental triggers. And while there is disagreement about the magnitude, nature, and mechanisms for such environmental factors, researchers have found seven genes prevalent among many individuals diagnosed as autistic.


There is little disagreement on the heritable component of autism. Originally hinting toward this was the observation that there is about a 60% concordance rate for autism in identical twins, while non-identical twins and other siblings only exhibit about 4% concordance rates.


A number of studies reveal that there are definite physical changes in the brains of individuals on the autism spectrum. The frontal lobes, cerebellum, hippocampus and amygdala are enlarged, while the corpus collosum is smaller than normal. Axons link our brain cells together, and in autistic individuals there are too many of these in local areas of the brain, and not enough linking different areas together. It is not known yet if these changes in the brain are the cause, or just effects, of Autism Spectrum Disorders.*


Click here to read more about Genetics as a cause of autism.


Possible environmental causes of autism

The search for environmental triggers has been mostly focused on trying to find a cause for a alleged rapid increase in the reported prevalence of autism in recent decades. The prevalence increase would appear to implicate recent changes in human lifestyle, but there is serious doubt as to whether the the incidence of Autism Spectrum Disorders is actually increasing. See the Is there an autism Epidemic? fact sheet.


A recent finding of an anomaly in the apparent lower rates of autism among the Amish community would seem to support the notion that modern lifestyle has to do with the prevalence increase. The Amish, however, are a very isolated community, genetically as well, so this finding does not necessarily shed any light on heritability without further study. It should be stressed that the Amish finding is very preliminary. Many of the environmental trigger theories are based on anecdotal accounts of regressive autism observed after a particular occurrence, vaccination being the most popular one among parents.


'Leaky gut' theory

It has been claimed that up to fifty percent of children with autism experience persistent gastrointestinal tract problems, ranging from mild to moderate degrees of inflammation in both the upper and lower intestinal tract. This has been described as a syndrome, autistic enterocolitis, by Dr. Andrew Wakefield; this diagnostic terminology, however, has been questioned by medical experts. Constipation, often with overflow, or encopresis, is often associated with developmental disorders in children, and is often difficult to resolve, especially among those with behavioral and communication problems. There are numerous medical conditions comorbid to Autism Spectrum Disorders, with colitis perhaps the most prevalent.


Infectious disease

The exponential increase of level one autism diagnoses, the least ambiguous diagnostic category, has led some researchers to hypothesize that the environmental trigger is quite literally an "autism epidemic", involving the exponential spread of an infectious disease agent such as virus or bacteria. One theory is of an intestinal virus disrupting the mucosa and allowing neurotoxins to enter the bloodstream. Another is that the Borna virus — suggested to be involved in schizophrenia, although some recent studies have not borne this out — is triggering autism among the genetically susceptible. Another hypothetical trigger is the herpes virus.


It should be noted though, that the exponential increase of autism diagnoses is debated too. Some researchers believe the increase is due rising awareness and changes in diagnostic criteria, not an environmental cause.


Heavy metal toxicity

Some parents and researchers have alleged that heavy metal poisoning, particularly that involving mercury, results in symptoms similar to those of autism. Despite this belief having been refuted, they propose that one of the following could be the case:
• Mercury poisoning in children may be a phenocopy of autism
• One of the liabilities of the autism genotype could be markedly reduced tolerance to heavy metal toxicity
• Mercury toxicity could simply amplify the symptoms of autism.


Some studies claim to have implicated mercury and other metals used in dental fillings as playing a role in the etiology of autism but rigorous research has failed to establish a link to date.


Vaccinations as an alleged cause of autism

A theory that is very popular among parents is that vaccines that use thimerosal as a preservative are to blame for the prevalence increase in cases of autism. Popularity in this theory may because the characteristics of autism often appear at around the same age vaccinations are carried out. Nevertheless, the link is inconclusive. Ip et al (2004) compared hair and blood mercury levels in autistic children with those of non-autistic controls and found a 10% increase in blood and hair mercury levels of autistic children, which is not statistically significant. Their results are questionable in that they chose to analyze mercury levels in children who were already diagnosed with autism.


If exposure to mercury at a particular stage in a child’s development were to make that child more susceptible to autism, studying children who already have autism will not find this link. Furthermore, their study looks at children with an average age of approximately seven years, whereas early onset autism (thought to be linked to thimerosal) has “onset prior to age three years” (DSM-IV). A more appropriate study would involve mercury levels in children prior to age three years.


The MMR vaccine for measles, rubella and mumps has also been claimed as a cause. Madsen et al (2003) found no reduction in the prevalence of autism in Denmark after MMR vaccination was phased out. However, this work has serious omissions in that they failed to look at vaccines containing thimerosal and did not differentiate between regressive autism (thought to be linked to MMR) and early onset autism (thought to be linked to thimerosal). For more information, click here.


Perinatal factors

Individuals diagnosed with Autism Spectrum Disorders have repeatedly been shown to have significantly higher incidence of prenatal and perinatal complications. This link does not demonstrate a causal relationship, however. Researchers have suggested that birth complications are the result of genetic predisposition.



Some studies have shown that autistic children are affected by stressful events more than their non-autistic counterparts (although a subset of them seem to be less affected by psychosocial stress in particular). The occurrence of autistic withdrawal under stress was suggested in the 1970s. More recently, the occurrence of “shutdowns” under social pressure has been recognized. Catatonia, which may be the result of psychological trauma, has been noted for its similarities with autism. A suggestive link can be drawn between stress and seizures and between seizures and regression.



Some researchers believe there is evidence for a yeast called candida albicans exacerbating many behavior and health problems in autistic individuals, if not possibly an actual cause of autism itself. Candida albicans is found in the digestive tract and is normally kept under control unless antibiotics allow an overgrowth. Proponents of this theory believe that behavior problems include irritability, confusion, hyperactivity, lethargy, short attention span and aggression. Research by a Dr. William Shaw has discovered unusual microbial metabolites in the urine of children on the autism spectrum who responded well to anti-fungal treatments, which lessened hyperactivity and self-stimulating behavior, and increases in eye contact, vocalization, and concentration. Proponents of this theory believe probiotic diets can help. Rigorous research has failed to definitely establish a link to date.



Since the 1950s up to the 1970s, it was believed that autism was the result of the faulty environment provided by uncaring “refrigerator mothers”, a theory that went largely unchallenged by psychologists at the time. This theory is discredited now, along with its main champion, Bruno Bettelheim. The Folstein-Rutter (1977) twin study is credited with shifting the focus from psychological factors to genetics. But in retrospect, it did not prevent other environmental theories from arising.

It was also observed that many mothers of autistic children were very loving. In cases where social interaction was found to be impaired between mother and child, it has been proposed this is simply due to social deficits in the child. Today, parent-blame theories are considered offensive. Hence, this is a sensitive topic, perhaps a reason why it has not been studied in recent decades.


There has been a general drastic shift in the focus of psychiatry in recent history, from theories based on early childhood psychological trauma to genetic and other neurological causes for disorders. Additionally, comparisons of twins reared apart with those reared together have shown that the shared environment (i.e. the family) is not as influential as the non-shared environment.


This is not to say that parenting is irrelevant. Some case reports have shown that profound institutional privation can result in quasi-autistic symptoms. Children genetically predisposed to autism are likely not immune to the effects of psychological privation, and in fact could be more sensitive to them. This also has some implications regarding institutionalization of autistic individuals, a practice still common today. The specific forms of institutional privation involved are unknown (though it is known that it is not nutritional privation). This information could presumably shed some light on subtle ways to affect the outcome of autistic individuals.


mirror neurons and autism

Some researchers claim there is a link between mirror neuron deficiency and autism. In typical children, EEG recordings from motor areas are suppressed when the child watches another person move, and this is believed to be an index of mirror neuron activity. However, this suppression is not seen in children with autism. Also, children with autism have less activity in mirror neuron regions of the brain when imitating . Based on these results, some researchers claim that autism is caused by a lack of mirror neurons, leading to disabilities in social skills, imitation, empathy and theory of mind. This is just one of many theories of autism and it has not yet been proven.


NON-MEDICAL VIEWS of autism & asperger therapies

There is a view that autism is not a disorder, but a normal, healthy variation in neurological hard-wiring, and therefore does not need to be cured. A cure is seen as destroying the original personality of the individual and is perceived similar to attempts to “cure” homosexuality, therefore this perspective considers the disease classification insulting. In line with this belief an autistic culture has begun to develop similar to deaf culture.


Another non-medical view is that there is no one condition called autism. This view was put forward by autistic author Donna Williams. She presents a holistic model called autism as a fruit salad model and demonstrated how the severity of someone's autism could be linked to their degree of co-morbid communication, sensory-perceptual, gut/immune, neurological integration, mood, anxiety and compulsive disorders a person inherited or developed, coupled with cognitive and learning style differences and unusual personality trait collections.


Click here to read a fact sheet on the debates on causes and diagnosis of Autism Spectrum Disorders.

* Source: David Amarai and Eric Courchesne, University of California

Click to close this Autism fact sheet on causes

Click here for the full range of autism and Asperger's fact sheets at www.autism-help.org
This autism fact sheet is licensed under the GNU Free Documentation. It is derivative of autism and Aspergers--related articles at http://en.wikipedia.org

The possible causes of Autism and Aspergers syndrome usually revolve around both genetic and environmental factors