By Melissa Lee Phillips
Neuroscience for Kids Consultant
February 28, 2003
Autism and Attention
Deficit Hyperactivity Disorder (ADHD) are two disorders commonly
diagnosed in children. Generally, both are first observed in the child's
early years, but some symptoms may persist into adulthood. Although a few
behaviors, such as inattentiveness and hyperactivity, are often seen in
both disorders, many of the behaviors associated with autism are distinct
from those of ADHD. Most researchers and doctors previously thought that
these two disorders were completely separate from one another and that the
behavioral signs were the only way these disorders could be diagnosed.
Now that we know more about the genetic makeup of humans, however,
scientists can search for the genetic causes for diseases and disorders.
One such search, published in the American Journal of Human
Genetics, reveals a surprising find: although autism and ADHD may be
different behaviorally, there is evidence that they may be caused, in
part, by the same gene.
Previous studies have suggested that a region on chromosome 16 is
likely to contain a gene contributing to the
development of autism. Researchers believe that children with an abnormal
version of this gene are more likely than other children to develop
autism. Dr. Susan Smalley and her fellow scientists at the University of
California in Los Angeles searched for regions of the genome that might
contain a "risk gene" for ADHD. They performed a genetic "scan" on 277
pairs of siblings, both of whom had been diagnosed with ADHD. This scan
allowed them to find areas on specific chromosomes that are likely to
contain genes contributing to ADHD. They found that the same area of
chromosome 16 that had been implicated in scans looking for autism genes
also showed up in their ADHD gene search. This was surprising because the
behavioral symptoms of each disorder can be so different. Some scientists
think this means that a gene on this chromosome
causes the behaviors that are similar in each disorder. Others believe
that there are certain genes in the genome that simply predispose people
to develop any of a variety of mental disorders. Other factors, such as
other genes and environmental influences, may determine which disorder the
person develops.
Autism and ADHD are most likely caused by the combined effects of many
genes and the effects of unknown environmental factors. It is very
unlikely that one gene on chromosome 16 will decide entirely whether
someone develops either of these disorders. It is also important for
other scientists to confirm these initial results. The researchers do not
know for sure that the same gene is contributing to both disorders.
However, if these results are supported by future studies, they would
point to a very interesting -- and as yet unexplained -- link between two
previously unlinked disorders. |