What is Autism?

When people refer to “Autism” today, they are usually talking about Autism Spectrum Disorders (ASD), which are five complex, brain-based disorders that affect a person’s behavior as well as social and communication skills. The Centers for Disease Control describes ASDs as:  "developmental disabilities that cause substantial impairments in social interaction and communication and the presence of unusual behaviors and interests. Many people with ASDs also have unusual ways of learning, paying attention, and reacting to different sensations. The thinking and learning abilities of people with ASDs can vary—from gifted to severely challenged. An ASD begins before the age of 3 and lasts throughout a person's life." 

Autism is four times more likely to affect boys than girls, and is found in all racial, ethnic, and social groups. There is no known single cause for autism, although the best available science points to important genetic components. Through twin studies, scientists have determined that autism is a genetically based condition. If one identical (monozygotic) twin has autism then there is an 80-90% chance that the other twin will also be diagnosed with an autism spectrum disorder. For non-identical (dizygotic) twins the chance is about 3-10% that both twins will develop autism spectrum disorder. The chance that siblings will both be affected by ASD is also about 3-10%. 

Scientists are unsure what, if any, environmental triggers may be involved in autism.  One theory, popular in the late 1990’s and early 2000’s, that vaccines cause autism, has since been disproven by numerous studies conducted around the world. 

Autism Spectrum Disorders are characterized by significant impairments in social interaction and communication skills, as well as by the presence of extremely challenging behaviors.  Such behaviors include repetitive motor behaviors (hand flapping, body rocking), insistence on sameness, resistance to change and, in some cases, aggression or self-injury. Many individuals with an autism spectrum disorder have significant cognitive impairments, although some have typical or even above average IQs.  30-50% of people with autism also have seizures.

Dr. Leo Kanner first described autism in 1943.  He reported on eleven children who showed a marked lack of interest in other people, but a highly unusual interest in the inanimate environment. Initially, autism was thought to be an early form of schizophrenia, which led to the belief that its onset could be caused by negative experience or bad parenting. We now know that this is not the case.

There are five Autism Spectrum Disorders, sometimes called Pervasive Developmental Disorders (PDD):

  • PDD-NOS (Pervasive Developmental Delay - Not Otherwise Specified).
  • Autism (sometimes referred to as Classic Autism, Early Infantile Autism, Childhood Autism, or Autistic Disorder)
  • Asperger Syndrome
  • Rett Syndrome
  • Childhood Disintegrative Disorder

Learn more about Autism Spectrum Disorder classifications and browse our autism quick facts.