The definition of autism has been refined over the years. Between 1995 and 2011, the DSM-IV grouped Asperger’s Syndrome and Pervasive Developmental Disorder Not Otherwise Specified (PDD-NOS) with autism. Asperger’s syndrome was an autism spectrum disorder marked by strong verbal language skills and, often, high intellectual ability. PDD-NOS was a more general diagnosis for people who did not fit clearly into the other two categories. 

However, the DSM-IV no longer recognizes Asperger’s syndrome or PDD-NOS as separate diagnoses. Individuals who would previously have received either of these diagnoses may now receive a diagnosis of autism spectrum disorder instead. 

Researchers have been working on autism and autism-like disorders since the 1940s. At that time, autism studies tended to be small in scale and used varying definitions of the disorder. Autism was also sometimes lumped in with other conditions.

Focused research into ASD became more common in the 1980s when the DSM-III established autism as a distinct diagnosis. Since then, researchers have explored the causes, symptoms, comorbidities, efficacy of treatments, and many other issues related to autism. 

Researchers have yet to discover a cause for autism. Many of the ideas put forth thus far have been disproven. Likely a combination of genetic, neurological, and environmental factors are at work. 

Individuals with autism may present a range of symptoms, such as: 

• Reduced eye contact

• Differences in body language

• Lack of facial expressions

• Not engaging in imaginative play

• Repeating gestures or sounds

• Closely focused interests

• Indifference to temperature extremes

These are just a few examples of the symptoms an individual with autism may experience. Any individual could have some, all, or none of these symptoms. Keep in mind that having these symptoms does not necessarily mean a person has autism. Only a qualified medical professional can diagnose autism spectrum disorder. 

Most importantly, an individual with autism is first and foremost an individual. Learning about the symptoms can help you start to understand the behaviors and challenges related to autism, but that’s not the same as getting to know the individual. Each person with autism has their own strengths, likes, dislikes, interests, challenges, and skills, just like you do. 

Psychiatrists and other clinicians rely on the fifth edition of the Diagnostic and Statistical Manual of Mental Disorders (DSM-5) to define autism and its symptoms. 

• Deficits in social communication and interaction

• Restricted, repetitive behaviors, interests, or activities

These symptoms appear early in a child’s development—although diagnosis may occur later. Autism is diagnosed when symptoms cause developmental challenges that are not better explained by other conditions.

For many years, a diagnosis of autism was rare, occurring in just one child out of 2,000. One reason for this was the diagnostic criteria. Autism was not clearly defined until 1980 when the disorder was included in the DSM-III. Before that time, some cases of autism spectrum disorder may have been mistaken for other conditions. 

Since the ’80s, the rate of autism has increased dramatically around the world. In March 2020, the US Federal Centers for Disease Control announced 1 in 54 children in the United States is affected by autism. 

Although autism is more likely to affect boys than girls, children of all genders have been diagnosed with ASD. Several recent studies investigate the impact of race, ethnicity, and socioeconomic disparities on the diagnosis of autism spectrum disorder.

When a person has more than two or more disorders, these conditions are known as comorbidities. Several comorbidities are common in people with autism. 

These include: 

• Anxiety

• Depression

• Epilepsy

• Gastrointestinal and immune function disorders

• Metabolic disorders

• Sleep disorders

Identifying co-occurring conditions can sometimes be a challenge because their symptoms may be mimicked or masked by autism symptoms. However, diagnosing and identifying these conditions can help avoid complications and improve the quality of life for individuals with autism.