Autism spectrum disorder (ASD) refers to a set of developmental disorders that impact communication, learning, and social skills. Because ASD is a spectrum, there are several different kinds of autism covered by the diagnosis. Here’s what you need to know about the different kinds of autism, past and present.

What different kinds of autism existed before ASD?

Several conditions that used to be diagnosed separately are now considered a part of the autism spectrum. Before the establishment of ASD in the Diagnostic and Statistical Manual of Mental Disorders 5 (DSM-5), there were several kinds of autism, including autistic disorder, pervasive developmental disorder not otherwise specified (PDD-NOS), and Asperger syndrome.

The DSM-4 identified the main features of autistic disorder as “the presence of markedly abnormal or impaired development in social interaction and communication, and a markedly restricted repertoire of activity and interest” and noted that the condition was also sometimes referred to as Early Infantile Autism, Childhood Autism, or Kanner’s Autism.

Asperger syndrome is also now a part of the autism spectrum, but in the DSM-4, it was a separate diagnosis, characterized by “severe and sustained impairment in social interaction and the development of restricted, repetitive patterns of behavior, interest, and activity.” The manual noted that Asperger syndrome differed from autistic disorder specifically in that it didn’t involve “clinically significant delays” in language, cognitive development or in the development of age-appropriate self-help skills, adaptive behavior, and curiosity about the environment in childhood.

Finally, according to the DSM-IV, PDD-NOS was used as an umbrella term encompassing other related conditions.

Are there different kinds of autism included in ASD?

Under the umbrella of autism spectrum disorder, there are still ways for clinicians to make distinctions between different “kinds” of autism. The DSM-5 describes three levels of autism:

• Level 1: Requiring Support — This is the least severe level and people in this level experience relatively mild issues. They might have a hard time initiating conversations or responding appropriately in social situations and lack flexibility.

• Level 2: Requiring Substantial Support — People with Level 2 diagnoses often struggle to communicate, both verbally (holding conversations and expressing themselves clearly) and nonverbally (maintaining eye contact and facing the person they’re speaking to). At Level 2, people with ASD might be so inflexible that it interferes with their daily functioning and even small changes to routines might cause them distress.

• Level 3: Requiring Very Substantial Support — This is the most severe diagnosis for people with ASD. People with a level 3 diagnosis have significant verbal and nonverbal communication impairments, which often leads them to avoid interactions with others. Their behaviors are the most inflexible and repetitive of any on the spectrum and they tend to react with high levels of distress in any situation that requires a change in focus.

While ASD now encompasses every kind of autism, the term refers to a range of developmental disorders, with wide variety when it comes to the intensity of the symptoms experienced.