CAUSES OF ASPERGER'S SYNDROME
The direct cause, or causes, of Asperger's
syndrome are unknown. Even though no consensus exists for the
causes of Asperger's syndrome, it is widely accepted that Asperger's
syndrome has a hereditary factor. It is suspected that multiple
genes play a part in causing Asperger syndrome, since the number
and severity of symptoms vary widely among individuals.
Genetics as a principal cause of Asperger Syndrome
Asperger described common symptoms among his patients'
family members, especially fathers, and research supports this observation
and suggests a genetic contribution to Asperger syndrome. Although
no specific gene has yet been identified, multiple factors are believed
to play a role in the expression of autism, given the phenotypic
variability seen in this group of children. Evidence for
a genetic link is the tendency for Aspergers syndrome to run in
families and an observed higher incidence of family members who
have behavioral symptoms similar to Aspergers syndrome but in a
more limited form (for example, slight difficulties with social
interaction, language, or reading). Most research suggests that
all Autism Spectrum Disorders have shared genetic mechanisms, but Aspergers syndrome may have a stronger genetic component than autism. There is
probably a common group of genes where particular alleles render
an individual vulnerable to developing Aspergers syndrome; if this
is the case, the particular combination of alleles would determine
the severity and symptoms for each individual with Aspergers syndrome.
to read more about Genetics as a cause of Asperger's syndrome.
teratogens as a possible cause of Asperger Syndrome
A few Autism Spectrum Disorder cases have been linked to exposure to
teratogens (agents that cause birth defects) during the first eight
weeks from conception. Although this does not exclude the possibility
that Autism Spectrum Disorders can be initiated or affected later, it is strong evidence
that it arises very early in development. Many environmental
factors have been hypothesized to act after birth, but none has
been confirmed by scientific investigation.
Mechanism of Asperger's syndrome
Asperger syndrome appears to result from developmental
factors that affect many or all functional brain systems, as opposed
to localized effects. Although the specific underpinnings of
Aspergers syndrome or factors that distinguish it from other Autism
Spectrum Disorders are unknown, and no clear pathology common to
individuals with Aspergers syndrome has emerged, it is still
possible that Aspergers syndrome's mechanism is separate from other
Autism Spectrum Disorders.
Neuroanatomical studies and the associations with
teratogens strongly suggest that the mechanism includes alteration
of brain development soon after conception. Abnormal migration
of embryonic cells during fetal development may affect the final
structure and connectivity of the brain, resulting in alterations
in the neural circuits that control thought and behavior. Several
theories of mechanism are available; none are likely to be complete
underconnectivity and mirror neuron theories
Functional magnetic resonance imaging provides
some evidence for both underconnectivity and mirror neuron theories..
The underconnectivity theory hypothesizes underfunctioning high-level
neural connections and synchronization, along with an excess of
low-level processes. It maps well to general-processing theories
such as weak central coherence theory, which hypothesizes that a
limited ability to see the big picture underlies the central disturbance
in Autism Spectrum Disorders.
mirror neuron theory
The mirror neuron system (MNS) theory hypothesizes
that alterations to the development of the MNS interfere with imitation
and lead to Asperger's core feature of social impairment.
For example, one study found that activation is delayed in the core
circuit for imitation in individuals with Aspergers syndrome.
This theory maps well to social cognition theories like the theory
of mind, which hypothesizes that autistic behavior arises from impairments
in ascribing mental states to oneself and others, or hyper-systemizing,
which hypothesizes that autistic individuals can systematize internal
operation to handle internal events but are less effective at empathizing
by handling events generated by other agents. Other possible
mechanisms include serotonin dysfunction and cerebellar dysfunction.
Possible environmental causes of Asperger's
The search for environmental triggers has been
mostly focused on trying to find a cause for a rapid increase in
the alleged increase
in autism in recent decades. The prevalence increase would appear
to implicate recent changes in human lifestyle, but there is considerable
disagreement as to whether the number of cases is actually increasing.
Research has focused on possibilities such as:
• Infectious disease
• Heavy metal toxicity
• Certain vaccinations
• Perinatal factors
More information on these is included in the Causes
of autism fact sheet.
The poor parenting myth
Since the 1950s up to the 1970s it was believed
that autism, and by association Aspergers syndrome, 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. Click here
to read a fact sheet on the "refrigerator mother" theory
as a cause of autism.
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