Understanding the Different Types of Autism

What Are The Five Types of Autism?

Autism Spectrum Disorder (ASD) is a neurodevelopmental disorder characterised by differences in the development of the brain.

Historically five types of Autism were categorised. However, today this classification is considered out of date. Today, the Diagnostic and Statistical Manual of Mental Disorders (DSM) shows that ASD exists on a continuum with different signs and symptoms.

Although the older terminology has been removed and people now received the diagnosis of Autism Spectrum Disorder, the previous terminology hasn't been eliminated from conversations. Therefore it becomes prudent to know the classification of these five types of autism.

The Transition from DSM-IV-TR To DSM-5

The transition from DSM-IV-TR to DSM-5 represented significant changes in how autism is defined.

In the DSM-IV-TR, autism was classified under the category of Pervasive Developmental Disorders (PDD). This category included five distinct diagnoses.

The separation of diagnoses such as Autistic Disorder, Asperger's Disorder, and Pervasive Developmental Disorder - Not Otherwise Specified (PDD - NOS) led to significant diagnostic overlap and inconsistency.

It was also proving challenging to the clinicians who were unable to apply the criteria consistently. This led to variability such that which diagnosis would be provided started to depend on who was performing the assessment.

Many individuals with similar symptoms were diagnosed differently based on subjective interpretations of the criteria.

DSM-5 aimed to address this by consolidating these categories into a single diagnosis of autism spectrum disorder (ASD), reflecting the understanding that autism exists on a spectrum rather than as a discrete disorder

The separate diagnoses of Autistic Disorder, Asperger's Disorder, and Pervasive Developmental Disorder - Not Otherwise Specified (PDD - NOS) were combined into a single diagnosis of ASD.

Rett's Disorder was removed from the Pervasive Developmental Disorders (PDD) category and placed under "Neurodevelopmental Disorders" due to its known genetic cause, and Childhood Disintegrative Disorder was incorporated into the broader ASD category.

Types of Autism

Kanner’s Syndrome

This is also known as classic autism. This is what people ‘think’ of when they hear the term autism. It is named after Leo Kanner, who in this classic 1943 study identified 11 children with distinct social and behavioural patterns.

Kanner noted now the children engaged in repetitive patterns of behaviour like flapping their hands and also had disinterest in their environment. He also noticed their struggle with change and the difficulty they experienced with speech such as echolalia (constant repetition of words).

Kanner’s Syndrome is classified by atypical behaviours, deficits in social communication, sensitivity to sensory stimuli, and restricted attention to interests and activities. They might exhibit ritualistic and compulsive behaviour that is time-consuming.

Around 10% or less percentage of autistic individuals have unique unusual abilities such as having extraordinary rare talent and showing exceptional aptitude in one particular domain (being a savant).

The disorder follows a steady course without remission and the symptom manifests in early childhood. Early intervention is recommended and proven to be beneficial for individuals with this disorder.

Augmentative and alternative communication (AAC), speech-language therapy, occupational therapy, etc. are recommended as treatment strategies that aim to alleviate or reduce symptoms and improve daily life skills and occupational functioning.

Rett Syndrome

Rett Syndrome is a genetic condition mostly occurring in girls. The disorder was identified by Dr. Andreas Rett in 1966 but it was not until 1983, when Dr. Bengt Hagberg published an article that the disorder received much recognition.

Affected individuals show symptoms like repetitive hand movements and difficulties with motor skills.

They also have various cognitive and physical impairments such as a decrease in head growth and loss of speech milestones. They might also have loss of muscle tone (hypotonia), jerky movements of the limb and difficulty in feeding.

The age of onset as well as the course of the disorder varies for every individual. Subtle abnormalities are present even in early infancy and then gradually as the child grows physical and mental abnormalities develop. Children with Rett syndrome also exhibited autistic-like symptoms.

Rett syndrome is no longer recognised as ASD since the DSM-5 publication, however, it is still linked to autism. Many children are initially diagnosed with autism before they are found to have the MECP2 gene mutation, which then changes their diagnosis to Rett syndrome.

Asperger's Syndrome

Asperger's Syndrome is now viewed as a milder form of autism. Hans Asperger in 1944 identified that despite having typical language development, certain individuals could be categorised based on shared differences in their social interactions with others. These individuals also exhibited a deep interest in certain topics.

Asperger's syndrome is considered a relatively milder form of ASD because it leaves the spoken language and intelligence unimpaired.

The inherent cause of this disorder has been difficult to discover. While it seems to have high heritability, brain imaging studies have failed to find a common cause for this syndrome.

Asperger's syndrome cannot be directly treated with medication. Pharmaceutical interventions are used to treat other disorders that might be comorbid. Therapy-based intervention is recommended to improve one's daily life skills and occupational skills.

Despite the reclassification, many individuals and professionals still use the term "Asperger's" to describe those at the higher-functioning end of the autism spectrum.

Childhood Disintegrative Disorder (CDD)

This was also known as Heller's syndrome. It is a rare neurodevelopmental disorder in which children have normal development until the age of three or four. After this, they seem to lose some of their acquired skills and developmental milestones such as language and speech skills.

Children affected by CDD even lose previously acquired vocabulary and adaptive behaviours. This leads to severe impairment in daily functioning. This regression is often rapid and causes extreme distress to both the caregivers and the child.

The cause of CDD is not clearly defined. However, it is known to stem from abnormalities in the brain structures and certain genetic and environmental factors. Treatments and interventions focus on providing support and improving quality of life. 

Pervasive Developmental Disorder - Not Otherwise Specified (PDD - NOS)

When individuals exhibit symptoms but don't meet the criteria for other types of autism, this diagnosis is given. This is also known as atypical autism.

It was often considered a "catch-all" diagnosis for those who didn't fully meet the criteria for more specific conditions such as autistic disorder or Asperger syndrome. This diagnosis has been largely replaced by the broader term "autism spectrum disorder" (ASD) with the publication of the DSM-5 in 2013.

Treatment for PDD-NOS was similar to that for other ASDs, focusing on tailored interventions to improve communication, social skills, and adaptive behaviours. These might include speech therapy, behavioural therapy, and educational support.

Early intervention is crucial for improving outcomes, and helping individuals develop essential skills for better integration into daily life.

The Three Functional Levels of Autism

DSM-5-TR provides severity ratings for autism spectrum disorder (ASD) that are classified into three levels. The three levels of autism describe how much support a person with autism needs. These levels are like labels that show how much support someone might need.

However, they don't always match how someone acts every day. Some people might show traits from different levels at different times, or they might change between levels from day to day.

Level 1: Requires Support

This is also known as high-functioning autism as level 1 indicates people who don't need a lot of support.

A person with level 1 ASD might show difficulty in social communication such as communicating using full sentences or engaging in back-and-forth conversation. They might also experience burnout from masking or camouflaging their symptoms.

Autistic people are often made to believe that to fit in, they need to suppress their neurodivergent traits and present neurotypical patterns of behaviour.

Therefore, masking, that is, suppressing their pattern of thoughts and behaviour, can be considered a social survival strategy. This also leads to difficulties in diagnosis.

They might find it hard to switch between activities or try new things. Also, they could struggle with organising and planning. Their independence might not match what's expected for someone their age who doesn't have autism.

Level 2: Requires Substantial Support

People diagnosed with ASD level 2 find it difficult to mask their neurodivergent patterns of behaviour. They are also unable to communicate in ways that make them easily understandable to others. They might also find it extremely difficult to move on from one activity to the next.

People with ASD level 2 exhibit repetitive behaviours and have very specific interests. They might also engage in stimming, such as packing back and forth and repeating what they have said. Stimming helps them to feel calm and better.

Everyone stims in some way or the other, such as tapping fingers or humming but autistic people stim more. This is primarily because the societal structures do not cater to the needs of autistic people and they have to bear the responsibility of their own emotions and reactions.

Level 2 autism is more intense and challenging in terms of managing social interaction and completing everyday tasks compared to Level 1.

Level 3: Requires Very Substantial Support

This can also be considered as low-functioning autism. Autistic people at this level show a very high risk for neglect, abuse and discrimination. People in this category have similar traits to those with level 1 and 2 autism, but they are unable to mask and hide their difficulties.

They have to work hard to control their emotions and reactions all the time and often fail in doing so.

The difficulties in social communication lead to level 3 autistic people rarely initiating conversations on their own, especially with neurotypical people. This is also because they are likely to be perceived as awkward.

They find it difficult to engage verbally as well as non-verbally. Completing daily tasks also becomes extremely challenging for them.

Assigning people to one of the three levels of autism can help decide what kind of services and support they might need. However, it doesn't capture all the unique things about someone's personality and behaviour. This means the help they get has to be tailored specifically to them.


Understanding the types of autism gives us insight into the historical roots of the disorder as well as the evolution of its conceptualization.

The transition from DSM-IV-TR to DSM-5 represented a significant shift towards recognizing autism as a spectrum disorder, acknowledging the heterogeneity of symptoms and the need for a more comprehensive diagnostic approach.

The consolidation of separate diagnoses into ASD reflects a more nuanced understanding of autism and facilitates more consistent diagnosis and intervention strategies.

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