Autism spectrum disorder (ASD) encompasses a wide range of neurological and developmental disorders. Autism can cause delays and disabilities related to learning, communication, social and motor skills, and behavior. Many people with autism also live with sensory sensitivities, seizures, gastrointestinal problems, anxiety disorders, and attention deficit and hyperactivity disorder (ADHD).

Autism is referred to as a spectrum because its effects can range from mild to very severe and debilitating. Some autistic people function independently for their age level, while others need assistance with basic functions for their entire lives. Approximately one-third of people with autism never begin talking, although many learn nonverbal forms of communication. Approximately one-third of autistic people have intellectual disabilities, while others have average or significantly above-average intellectual abilities. Despite these differences, most people with ASD share difficulties in communicating, recognizing social cues, relating to others, and navigating transitions. Repetitive behavior and intense interest in very specific topics or objects are also commonly shared characteristics. Read more about behaviors and other symptoms of autism.

Autism spectrum disorder includes several conditions that were considered distinct diagnoses until the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) was published by the American Psychiatric Association in 2013. Since the release of the DSM-5, professionals who work with children on the autism spectrum have accepted Asperger syndrome, childhood disintegrative disorder (CDD), and pervasive developmental disorders not otherwise specified (PDD-NOS) as part of ASD rather than separate conditions. Read more about former and current classification of autism.

The History of Autism

Before the 20th century, autism was not distinguished from mental illness, epilepsy, or other neurological disorders that caused unusual behavior or developmental disabilities. Based on cave art dating from 6,500 BCE, anthropologists believe that early man treated seizures and mental illness with trepanation, or drilling a hole into the skull, possibly to free the evil spirits they believed were causing the symptoms.

In many ancient societies, including Greece and Rome, children with physical or cognitive disabilities were considered liabilities, and some authorities mandated that disabled children be drowned or abandoned to die. In other civilizations, people with developmental disabilities were expected to earn their living by begging or made figures of entertainment as jesters in wealthy homes. Many cultures and religious traditions around the world considered children with developmental difficulties or seizures as possessed by demons, or punishment for the sins of their parents.

In the Middle Ages, the Roman Catholic church founded orphanages, hospitals, and other institutions where people with various disabilities could be left by their families to receive basic food and shelter, if little else. Some European villages maintained cages in which developmentally disabled people, known as “idiots,” were kept for protection, punishment, or entertainment. According to legend, some towns would pay sailors to carry away their disabled and mentally ill to distant lands on a “ship of fools,” where they would be left to try to survive. Witch hunting, widespread during this period, likely targeted many with neurological disorders - especially women.

One bright spot was the Belgian town of Geel, where Dymphna, the patron saint of mental illness, died in 600 CE. Disabled or mentally ill people would be brought to the shrine of St. Dymphna in the hope of a cure, and often be left behind. By the 1500s, Geel had a thriving foster system in which disabled people were lodged with local families and cared for out of a sense of religious duty. Fostering those with mental or developmental disabilities remains a strong tradition in Geel, and hundreds of families there still foster people – including those with autism – in their homes today.

In the 16th century, the Renaissance brought a somewhat more scientific view of those with developmental disabilities as suffering from medical conditions rather than demonic possession. However, most Western cultures deemed it important to separate those whose behavior or abilities seemed abnormal from the rest of society. Governments built large institutions to house the disabled. Conditions were bleak, as those with mental disorders were considered to be more like animals than people. Many inmates of these asylums were chained up, treated with blood-letting and laxatives, and sometimes exhibited for a fee to curious crowds.

In the 18th and 19th centuries, people began to view this type of treatment as inhumane, and institutional conditions slowly improved. Even with more humanitarian aims, asylums frequently became overcrowded and understaffed, and treatments were usually ineffective.

The word “autism,” from the Greek autos, meaning self, was first used in 1908 by Swiss psychiatrist Eugen Bleuler to describe schizophrenic patients who were especially withdrawn into themselves. Autism remained classified as a subset of schizophrenia in the Diagnostic and Statistical Manual of Mental Disorders (DSM) for many years.

In 1943, American psychiatrist Leo Kanner published a study on children who displayed high intelligence, a desire for aloneness, and "an obsessive insistence on persistent sameness." He termed this disorder “early infantile autism.” At this time, the psychoanalytic theories of Sigmund Freud – especially the belief that early mother-child relationships shaped lifelong mental health – were widely accepted. Influenced by Freud’s theories, Kanner suggested that cold, intellectual mothers contributed to the development of autism.

In 1944, Austrian pediatrician Hans Asperger published a description of boys who were highly intelligent and socially isolated, with specific, obsessive interests and poor motor skills. Asperger’s works were written in German and did not receive a wide audience at that time. Meanwhile, in Nazi-era Germany, the policy toward anyone deemed mentally disabled was euthanasia.

In the 1960s Bruno Bettelheim, an Austrian-American child psychologist, popularized the theory that “refrigerator mothers” caused autism by failing to provide enough affection. Bettelheim compared the life of autistic children to his experiences in a Nazi concentration camp during World War II and suggested that the mothers of autistic children were like Nazi soldiers guarding the camps. Parents were told they were to blame for their autistic children’s condition.

Bernard Rimland, an American research psychologist and the father of an autistic child, published a book in 1964 that attacked Bettelheim’s theories and made the first case for autism as a biological condition. In 1969, Rimland founded an organization with other parents of autistic children that is now known as the Autism Society of America. Bettelheim’s “refrigerator mother” theory was discredited within a few years, and in 1977, new research indicated that genetic influences and neurobiology play a strong role in causing autism.

“Infantile autism” was listed separately from childhood schizophrenia in the DSM-III in 1980 and replaced with “autism disorder” in the revised edition, the 1987 DSM-III-R. In the 1980s, the work of Hans Asperger was widely translated and published, shedding more light on the autistic spectrum. In 1991, the U.S. government recognized autism as a category of special education, mandating diagnosis and services for autistic children. Asperger syndrome was added to the DSM-IV in 1994.

In the 1990s, Norwegian-American psychologist Ole Ivar Lovaas pioneered the use of applied behavior analysis (ABA) and discrete trial training (DTT) as treatment for autistic children. The effectiveness of these intensive therapy methods has been proven over the subsequent decades.

In 1998, autism research was derailed by the publication of English gastroenterologist Andrew Wakefield’s theory that the measles-mumps-rubella (MMR) vaccine caused the development of autism in 12 children he studied. Wakefield was found to have falsified and manipulated data and accused of conflicts of interest. Wakefield’s theory was quickly debunked by other scientists, and his article was officially retracted in 2010.

In the American Psychiatric Association’s 2013 manual, the DSM-5, the term “autism spectrum disorder” is used to describe the range of related developmental disabilities under two categories: social communication and restricted or repetitive behaviors. Types of autism such as Asperger syndrome are no longer listed as separate diagnoses in the DSM-5, but included under ASD.

Although it is impossible to know for sure, many famous and talented people in history are conjectured to have been on the spectrum of autistic disorders. Experts in autism have suggested that Wolfgang Amadeus Mozart, Michelangelo, Sir Isaac Newton, Charles Darwin, Emily Dickinson, and Albert Einstein were all likely autistic.

How Common Is Autism?

It is estimated that in the United States 1.6 percent of children, or one in 59, have autism – this estimate includes one in 37 boys and one in 151 girls. Autism is more difficult to diagnose in adults, making it harder to estimate how many adults live with autism. Worldwide, between 1 and 2 percent of people are believed to be on the autism spectrum. Boys are about four times more likely to be diagnosed with autism as girls. New studies suggest that symptoms of autism may differ in girls, making them less likely to be diagnosed. All races, ethnicities, and socioeconomic classes are equally affected by autism.

How Is Autism Diagnosed?

There is no one single conclusive test for autism. There are differences between screenings at well-child visits, school evaluations, and medical diagnoses. An autism screening does not provide a diagnosis but checks for red flags that might indicate a need for further evaluation. A school evaluation or educational determination is made by a team of education professionals and focuses on rating the level of disability. Medical diagnosis is performed by a doctor such as a developmental pediatrician, child psychologist, child psychiatrist, or neuropsychologist. For a medical diagnosis, the doctor will ask questions about the child’s developmental history, assess symptoms, and test cognitive abilities, language skills, and age-appropriate physical skills.

While some children may show signs of autism within the first few months of life, most are diagnosed between ages 3 and 6. Older children and adolescents may be recommended for evaluation and diagnosis by teachers. Diagnosing autism in adults is more complex. Read more about how autism is diagnosed.

How Is Autism Treated?

Treatment for autism depends largely on the individual and what challenges they face. Behavioral therapies are the mainstay of treatment for most autistic people. Those who need it may also receive speech-language therapy, social skills training, and occupational therapy. Parents may also receive training on how better to work with their autistic child at home. Intense early intervention has been shown to be highly effective, and there are an array of programs geared to different types of needs. School-aged children may receive autism services through their Individualized Education Program (IEP), which is developed each year by a team of educational professionals with input from parents. Adults with autism may benefit from vocational services or other types of support.

Anti-epileptic drugs (AEDs) may be prescribed for children who have seizures. Parents of autistic children with harmful behaviors that are not effectively modified by therapy may choose to add medications such as antidepressants for obsessive-compulsive behavior or anxiety, antipsychotics, or drugs to help with attention deficit hyperactivity disorder (ADHD).

Read more about treatments for autism.

What Causes Autism?

The cause of autism is not yet known, but there is evidence that both genetic and environmental factors raise the risk of developing ASD. Siblings and children of those on the autistic spectrum are more likely to be autistic themselves. Children of older parents are more likely to have autism. Some medications taken during pregnancy increase the risk for having an autistic child. More studies are underway to pinpoint causes of ASD.

Condition Guide

• Autism – The Path to Diagnosis
• Autism Types and Classification
• Behaviors and Other Symptoms of Autism
• Treatments for Autism