Causes of Autism

Across the country, states, local school systems, and early intervention programs are reporting significant increases in the number of children with autism in their jurisdictions. The improvement in diagnostic criteria and tools has supported the diagnosis of children who were previously undiagnosed or were diagnosed with other disabilities, including those children falling at either end of the autism continuum: including those with severe to profound mental retardation, as well as those with normal to high intellectual abilities.

Even with improved diagnostic tools, however, there appears to be a real increase in the number of children with autism spectrum disorders. Many researchers and research institutes, including the Centers for Disease Control and Prevention (CDC), are researching the various factors that may play a role in the increasing rate of autism.

The CDC has recently implemented a project that will set up a system for accurately estimating the prevalence of autism in the United States and tracking it over time. To begin with, autism and autism spectrum disorder prevalence will be estimated each year using the same common, standardized, scientific methodology in six different regions of the country.

One of these six regions is comprised of Delaware and northeastern Maryland, including Baltimore City and Baltimore, Carroll, Cecil, Harford, and Howard Counties. The Maryland-Delaware site has the support of the Maryland State Department of Education and Department of Health and Mental Hygiene and is housed at the Johns Hopkins Bloomberg School of Public Health.

Medical researchers are exploring different explanations for the various forms of autism. Although no single cause of autism is known, current research links autism to biological or neurological differences in the brain. Scans, such as the MRI (Magnetic Resonance Imaging) and PET (Positron Emission Tomography), show abnormalities in the structure of the brain, with significant differences within the cerebellum, including the size and number of Purkinje cells.

In some families, there appears to be a pattern of autism or related disabilities. This suggests a genetic basis to the disorder, although no one gene has been directly linked to autism. In all likelihood, research will show that several genes (and perhaps environmental factors) are involved.

Research suggests that autism is a brain-based disorder, apparently of prenatal origin. The age at which symptoms of autism manifest themselves is not yet known, but may be as early as infancy. For younger siblings of children with autism, the recurrence risk of autism has been estimated as between five and nine percent.

Research into the genetic basis of autism is being conducted at a variety of levels. It is hoped that identification of the responsible genes will bring a broader understanding of the impact on brain development and function. This understanding may result in more effective treatments for individuals with autism.

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