CAUSES OF AUTISM
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.
Stress
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.
Yeast
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.
Parenting
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 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
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