Explaining child disorders
 

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Article #3: Causes of autism

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The causes and etiology of autism are Research has not yet established exactly
areas of debate and controversy; there is what is specific to autism and what may
currently no consensus, and researchers be seen in other disorders however.
are studying a wide range of possible Individuals with autism are also far more
genetic and environmental causes. Since likely to develop epilepsy than would
the way autism manifests is different for otherwise be expected (estimated 10-30%
each person, there are likely multiple incidence).
"causes" that interact with each other in Genetic component
subtle and complex ways, and thus give Genetic influence comprises a significant
slightly differing outcomes in each aspect of research in the causes of
individual. Two environmental theories autism. A large database showing
include the impact of vaccines on the theoretical links between autism and
immune system (of which a statistically genetic loci summarises research
significant link has never been found indicating that the genetic influence may
despite many attempts; see the vaccine extend to every human chromosome. It has
theory for a more extensive treatment) been observed in one twin-study in
and a more recent theory relating autism Britain that there was about a 60%
to high levels of television viewing concordance rate for autism in
while young. A correlation has also been monozygotic (identical) twins, while
found between autism and the mercury dizygotic (non-identical) twins and other
emitted from coal power plants, though siblings comparatively exhibited about 4%
the implications of this correlation is concordance rates. Some research posits
uncertain. Mercury measurements of hair that the chances that an identical twin
samples from autistic children's first of an autistic person will also be
haircuts were significantly lower than a autistic are 85-90%. The increased
matched group of normal children, probabilities of siblings having autism
declining as measures of severity has been calculated at about 35-fold more
increased. than normal.
Research claims also link autism with Accompanying impairments are also a
abnormal blood vessel function, and common feature of autism. Some people
oxidative stress. This line of research with autism also have gastrointestinal,
may lead to new medical therapies. immunological or neurological symptoms in
Physiology and neurology addition to behavioral impairments. These
Autism appears to involve a greater associated complexes have also lead to
amount of the brain than previously the search for specific genetic
thought. A study of 112 children (56 with connections and helped to focus on
autism and 56 without), published in the reasonable genetic implications.
Journal of Child Neuropsychology, found Since genes provide the information for
those with autism to have more problems processes and structure at the level of
with complex tasks, such as tying their the cell and its components during the
shoelaces or writing, which suggests that growth and development of a human as well
many areas of the brain are involved. as maintenance during life, gene
Children with autism performed simple mutations (altered versions) and
tasks as well as or better than those deletions (complete absence of genetic
without. In tests of visual and spatial material) and possibly extra copies of
skills, autistic children did well at genes would mean that the causes of
finding small objects in complex pictures autism begin very early. If a mutated
(e.g., finding the character Waldo in gene fails to perform properly, then
"Where's Waldo" pictures). However, they cells, proteins, enzymes and other
found it difficult to tell the difference crucial aspects of normal function may be
between similar-looking people. Children significantly altered and operate
with autism tended to do well in spelling incorrectly. Deletions could mean the
and grammar, but found it much more complete absence of a sequence of events
difficult to understand complex speech, due to missing proteins or cell
such as idioms or similes when the components for example. These genetic
meaning of the phrase is figurative. They alterations and deletions will simply
would, for example, not understand that bring about a changed structure or
"He kicked the bucket" meant someone had process which effects a great many other
died, or were likely to actually hop if needed structures and processes.
told to "hop to it". Another important aspect of research in
The inference from this research, genetic factors is environmental effects
according to researchers at the and the incidence of autism. During the
Pittsburgh School of Medicine, is that lifetime of a person, gene mutations and
"These findings show that you cannot deletions may be environmentally
compartmentalize autism. It's much more triggered or exacerbated. Conversely, it
complex.” may also be that environment will not be
The research from this perspective has a a factor and nothing will change the
number of implications: autism characteristics. For autism, the
Autism is more than likely a global answer to these possible explanations is
disorder which affects how the brain still being researched and there is
processes the information it receives, evidence that both may be true simply
while complex information tends to make because there is more than one way a
this more readily apparent. person may develop autism.
Neurological ‘wiring’ in people with Deletions and Mutations
autism manifest abnormalities in the Deleted genes have been noted as a
areas of the brain that communicate with probable influence or cause in autism. By
each other. locating specific missing genetic
Observed abnormalities provide a material the significance may be that
reasonable explanation for why children specific genetic sites for autism
with autism have problems with complex controlling or causing autism (autism
tasks which require multiple areas of the susceptibility alleles) may be located
brain to work together; autistic people precisely. Another significant aspect of
tend to do better in tasks that only this research is that these deletions of
require one region of the brain. genetic material indicate that autism may
The causes of autism are possibly more be established in some cases during
pervasive than previously believed; for meiosis (error-prone meiosis model) and
example, more areas of the brain are this places the genesis of autism in some
affected than just those involving social at the very beginning of life.
interaction, communication, interests, One very important question in this line
and imagination. of research is whether or not gene
Autism may not be primarily a disorder of deletions are a cause or consequence of
social interaction; research must now autism-susceptibility loci located
take into account non-social aspects. elsewhere in the chromosomes.
A possible explanation for the Gene mutations may mean a gene does not
characteristics of the syndrome is a function at all or does not function in
variation in the way the brain itself the normal way. Since genes direct how
reacts to sensory input and how parts of the body grows and develops, mutations,
the brain then handle the information. An like deletions, will effect a person at
electroencephalographic (EEG) study of 36 the most basic levels.
adults (half of whom had autism) at Mutation and deletion effects have been
Washington University in St. Louis found delineated in numerous research
that adults with autism show differences publications.
in the manner in which neural activity is Correlated characteristics include global
coordinated. The implication seems to be developmental delay, mild to severe delay
that there is poor internal communication of speech, social communication disorders
between different areas of the brain. and cognitive abilities, autistic like
(Electroencephalographs, or EEGs, measure behaviour, high tolerance of pain, and
the activity of brain cells.) repetitive mannerisms (e.g. chewing or
The study indicated that there were mouthing).
abnormal patterns in the way the brain Gene interaction may also complicate the
cells were connected in the temporal lobe causes leading to multiple genetic
of the brain. (The temporal lobe deals origins of autism, In a cascade like
with language.) These abnormal patterns effect, when a gene loci is altered or
would seem to indicate inefficient and omitted, others are effected due to
inconsistent communication inside the change in interaction between genes and
brain of autistic people. or their functions.
Studies in neuropathology indicate Though not present in all individuals
abnormalities in the amygdala, with autism, these mutations and
hippocampus, septum, mamillary bodies, deletions hold potential to point the way
limbic system, and the cerebellum. to more the genetic components of
Autistic brains are slightly larger and spectrum disorders. The research also
heavier and a larger than normal head advanced basic understanding in the
circumference is commonly noted. genetic architecture of the genome of
In the limbic system, there is an excess autistic individuals and will help in
of cells and they are too small. The focusing future research.
neurons themselves appear to be One practical aspect of this type of
underdeveloped. Dendritic trees which research may be the development of a test
provide the basis for connections between that would confirm the autism diagnosis
neurons are truncated (i.e. shortened). in children exhibiting symptoms and
In the cerebellum, purkinje cells are identify families who carry genetic
widely affected. The anatomic differences defects that could be inherited by their
correlate to the curtailment of children.
development earlier than 30 weeks Mirror neurons
gestation. In other words, the A theory featuring mirror neurons states
development of the cells appears to have that autism may involve a dysfunction of
stopped at some time before the 30th week specialized neurons in the brain that
in utero should activate when observing other
An enlarged third ventricle of the brain people. In typically-developing people,
appears to accompany autism in those who these mirror neurons are thought to
are non-mentally retarded, but the perhaps play a major part in social
reasons for this and its effects are learning and general comprehension of the
still unknown. actions of others.






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