The number of children diagnosed with autism or related disorders has grown at what many call an alarming rate. In the 1970s and 1980s, about one out of every 2,000 children had autism.
Today, the CDC estimates that one in 150 8-year-olds in the U.S. has an autism spectrum disorder, or ASD. This expanded definition refers not only to autism but also to a collection of brain development disorders such as Asperger's syndrome and a condition known as pervasive developmental disorder -- not otherwise specified (PDD-NOS). Though all the disorders share some symptoms, they are different in other ways, including the timeline of symptoms and the severity, according to the CDC.
Autism spectrum disorders include social, communication, and behavioral challenges. These problems can be mild, severe, or somewhere in between.
What Are the Types of Autism Spectrum Disorders?
WebMD explains autism spectrum disorders, including Asperger's syndrome, Rett syndrome, PDD-NOS, and childhood disintegrative disorder.
The apparent rise in cases triggers two burning questions for parents, physicians, and scientists:
Is autism truly on the rise, or do the new statistics simply reflect the growing awareness of the condition, the expanded definition, and other factors?
If autism is on the rise, as most experts believe, what is causing the increase?
(Does someone you love have autism? Join other parents and caregivers on WebMD's Autism Support Group message board.)
Autism: A True Increase or Semantics?
The jump in autism cases has spawned not only alarm but also debate about whether the number of children with autism could have increased that much in a relatively brief time.
"There's a lot of controversy about that," says Jeff Milunsky, MD, director of clinical genetics and associate director of the Center for Human Genetics at Boston University.
Two researchers who tracked the rate of autism in children born in the same area of England from 1992 to 1995 and then from 1996 to 1998 found that the rates were comparable, and concluded that the incidence of autism was stable. The study was published in the American Journal of Psychiatry in 2005.
But, Milunsky says, several studies have documented an increase in the U.S.
In a recent report in the journal Archives of Disease in Childhood, Milunsky and his colleagues point to several studies finding an increase in autism rates. In 2003, for instance, a large study conducted in Atlanta found that one in 166 to one in 250 children had autism, according to a report published in the Journal of the American Medical Association.