Autism disorders result from slight changes in genes that govern brain structure, suggests a study from France's Pasteur Institute.

Autism and related diseases, broadly known as autism spectrum disorders, are among the most genetic of all psychiatric and neurological problems. Genetic changes are thought to be present in 3 percent to 6 percent of all cases.

What Raises a Baby's Risk of Autism?

What kinds of changes are important? It looks like even small changes -- resulting in either too much or too little gene function -- affect how well people can use language and how well they can interact with others.

There's no single autism gene. However, changes in a certain region of one human chromosome are often seen in people with autism spectrum disorders.

SHANK3 is the name of one of the three genes in this part of the chromosome.

Researchers Thomas Bourgeron, PhD, and colleagues at the Pasteur Institute in Paris painstakingly evaluated the SHANK3 gene in more than 200 people with autism spectrum disorders. They found the gene in three families.

An individual in one family had a large part of the gene missing. This person was unable to speak and had moderate mental retardation.

Two brothers in a second family were missing just a small part of the gene. Yet they had severely impaired speech and severe mental retardation.

A girl in a third family was missing just the end piece of the SHANK3 gene. She had autism and severe language delay. Her brother, however, had an extra copy of the SHANK3 gene. He had Asperger syndrome -- one of the mildest autism spectrum disorders -- but fluent speech.

The SHANK3 gene is involved in organizing brain structure. Bourgeron and colleagues conclude that people properly develop speech, language, and social skills only when they have exactly the right "dosage" of this and other autism-related genes.

The researchers report their findings in the advance online edition of Nature Genetics.


Brains of Autistic Kids May Be Bigger

By Daniel J. DeNoon, reviewed by Louise Chang, MD

SOURCE: Durand, C. Nature Genetics, 2006; early online edition.