Autism spectrum disorders: anything but rare?


It may seem odd to see autism spectrum disorders (ASD) listed on a website for rare and orphan diseases. According to a recent report from the Center for Disease Control, about 1 in 88 children in the United States has an autism spectrum disorder, a 23 percent increase over rates the federal agency reported in 2009.

It is still unclear how much of the increase is due to heightened awareness of autism and to changes in the way the disorder is diagnosed. There is no clear-cut medical test that can diagnose autism. Instead, specially trained physicians and psychologists administer specific evaluations.

What is autism and what causes it?

Autism is a general term for a group of complex neurodevelopmental disorders with symptoms ranging from mild to severe. This group of brain-development disorders has been characterized as a "spectrum," reflecting both the varying severity of disease symptoms and the variety of disorders — from rare to familiar — that ASD encompasses.

Studies of twins and families indicate a genetic basis for ASD susceptibility, yet we know that genetics is not the whole story. Many experts theorize that, with the right mix of susceptibility genes, exposure to environmental factors might be necessary for autism to develop in some individuals.

Scientists have made significant breakthroughs in understanding the genetics of autism. Researchers are now focusing on specific chromosomal regions that may contain autism-related genes. The duplication of human chromosome 15q11-q13 is known to be the most frequent cytogenetic abnormality observed in autism. This chromosomal region has now been duplicated in mice, which exhibit many autism-related behaviors.

Rare forms of autism

There are many rare genetic conditions that present with autism. Rett syndrome Fragile X syndrome Timothy syndrome, and tuberous sclerosis complex are examples of rare disorders in humans that affect behavior and cognition.

Many mouse models have been developed that genetically typify these human mutations. The Jackson Laboratory and the Simons Foundation Autism Research Initiative are working together to make many of these mice available to researchers. Research on these animal models has helped scientists gain insight into treatment for some of these conditions, with clinical trials currently in progress.