Are There Accompanying Disorders?
Several disorders commonly accompany autism. To some extent, these
may be caused by a common underlying problem in brain functioning.
Mental retardation
Of the problems that can occur with autism, mental retardation is the
most widespread. Seventy-five to 80 percent of people with autism
are mentally retarded to some extent. Fifteen to 20 percent are
considered severely retarded, with IQs below 35. (A score of 100
represents average intelligence.) But autism does not necessarily
correspond with mental impairment. More than 10 percent of people
with autism have an average or above average IQ. A few show exceptional
intelligence.
Interpreting IQ scores is difficult, however, because most intelligence
tests are not designed for people with autism. People with autism
do not perceive or relate to their environment in typical ways.
When tested, some areas of ability are normal or even above average,
and some areas may be especially weak. For example, a child with
autism may do extremely well on the parts of the test that measure
visual skills but earn low scores on the language subtests.
Seizures
About one-third of the children with autism develop seizures, starting
either in early childhood or adolescence. Researchers are trying
to learn if there is any significance to the time of onset, since
the seizures often first appear when certain neurotransmitters
become active.
Since seizures range from brief blackouts to full-blown body
convulsions, an electroencephalogram (EEG) can help confirm their
presence. Fortunately, in most cases, seizures can be controlled
with medication.
Fragile X
One disorder, Fragile X syndrome, has been found in about 10 percent
of people with autism, mostly males. This inherited disorder is
named for a defective piece of the X-chromosome that appears pinched
and fragile when seen under a microscope. People who inherit this
faulty bit of genetic code are more likely to have mental retardation
and many of the same symptoms as autism along with unusual physical
features that are not typical of autism.
Tuberous Sclerosis
There is also some relationship between autism and Tuberous Sclerosis,
a genetic condition that causes abnormal tissue growth in the
brain and problems in other organs. Although Tuberous Sclerosis
is a rare disorder, occurring less than once in 10,000 births,
about a fourth of those affected are also autistic.
Scientists are exploring genetic conditions such as Fragile X and
Tuberous Sclerosis to see why they so often coincide with autism. Understanding
exactly how these conditions disrupt normal brain development may provide
insights to the biological and genetic mechanisms of autism.
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