People with atypical autism have some of the classic autism symptoms, but not enough to meet the required criteria for childhood autism or autism spectrum disorder.

Atypical autism is sometimes diagnosed when there is a late onset of symptoms. It is not to be confused with high-functioning autism.

Atypical autism used to be clinically known as pervasive developmental disorder not otherwise specified (PDD-NOS). It is also known as a subthreshold diagnosis.

What Is Atypical Autism?

The understandings and definitions of atypical autism are contested, with different researchers and clinicians reaching contrasting conclusions on its causes, symptoms, diagnoses, and other features. As recently as 2018, the Encyclopedia of Autism Spectrum Disorders went so far as to say that atypical autism is both “poorly defined” and “poorly understood.”

The Current Developmental Disorders Reports journal lists atypical autism as one of the subgroups of the disability. It was first included in the Diagnostic and Statistical Manual of Mental Disorder, Fourth Edition to cover the many cases of children who had only some symptoms of autism, but lacked some of the other defining ones. DSM-IV listed five separate diagnostic categories of autism, and PDD-NOS was one of them. This categorization was in effect from 1994 to 2013. 

PDD-NOS was defined as symptoms of autism that didn’t meet the criteria for recognized autism disorder because of a combination of factors, such as late-onset, subthreshold symptoms, and atypical symptoms. 

In order to be diagnosed with atypical autism, a person had to show significant impairment in the development of verbal and nonverbal skills, to the point of affecting social interaction. Additionally, if the criteria for other mood, behavioral, and developmental disorders (such as schizophrenia or avoidant personality disorder, to name two) were not met, but classic behavior, interests, and activities were still present, this would also likely lead to a diagnosis of atypical autism. 

In 2013, the American Psychiatric Association released the fifth version of the Diagnostic and Statistical Manual of Mental Disorders, where the category of “pervasive developmental disorders” was removed, and the diagnosis of pervasive developmental disorders not otherwise specified was also removed. DSM-5 consolidated what had been five categories of autism disorder into two: repetitive and restricted movements, and delays in communication and interaction.

Subthreshold Autism

Subthreshold autism is the term that refers to a person who has some features of autism, but not all of them. It is also used to describe a person’s condition when the symptoms of their autism are comparatively mild. An example might be a person who has significant social impairments but shows none of the repetitive behaviors, such as rocking back and forth or flapping their hands.

This means that people with atypical autism display great variations in their abilities and their challenges, which can make diagnosing the disorder difficult. 

Atypical Autism: The Symptoms

The characteristics of atypical autism are similar to those associated with the standard diagnosis for autism disorder, but they are on the milder side. They include:

  • Inappropriate or unusual social behavior.
  • Irregular development of fine or large motor skills, cognitive skills, or visual or spatial perception.
  • Slow development in speech or language comprehension.
  • Losses in nonverbal and verbal communication.
  • Changes in sensitivity to taste, sight, sound, smell, and tactile sensations.
  • Repetitive or ritualistic behaviors, especially when stressed.

Atypical autism might present with milder symptoms, but even people who have this form of autism can struggle substantially. Researchers writing in the Journal of the American Academy of Child and Adolescent Psychiatry compared people with atypical autism to those who had autism disorder and Asperger’s syndrome. They wrote that half of the children with atypical autism had so few of the repetitive behaviors that are so indicative of autism that they didn’t meet the criteria for the disability. Another quarter of the children had only passing language delays or mild cognitive developmental delays. The other quarter had a late age of onset or were too young to satisfy the required diagnosis for autism.

Even in cases where the atypical autism diagnosis confirms symptoms that are relatively mild, clinicians would recommend using standard treatments that apply across the autism spectrum: speech, occupational, and physical therapy; behavior and developmental therapy; and classes for older children that focus on social skills.

Diagnosing Atypical Autism

How can atypical autism be recognized? Parents and caregivers should look for the telltale social and communication delays, which can present themselves as early as infancy. This can look like difficulty using and comprehending language concepts, trouble connecting to other children, unusual habits while playing with toys, struggles to adapt to changes in routine and surroundings, and the stereotypical repetitive body movements.

Notwithstanding the similarities to classic autism symptoms, atypical autism can be tough to pin down because its own symptoms can be mild, or less disruptive, than those of autism disorder. If autism is suspected (or if other evidence, such as behavioral history, communication patterns, and neuropsychological functioning, is available), early intervention can steer parents toward therapy to address the problems and loss of specific skills. Developmental testing can be done as part of a standard wellness checkup.

Implications for Adulthood

People who are diagnosed with atypical autism are still likely to struggle with limitations similar to those of classic autism spectrum disorder.

Researchers in the Journal of Autism and Developmental Disorders found that even people with typical abilities in cognitive skills and language abilities will nonetheless encounter adulthood challenges. Even the atypical form of autism will place some limitations on their understanding of social context and emotional expressions.

Those diagnosed with atypical autism have an equal chance of getting married or holding down a job, when compared to those who have more severe presentations of autism.

This is where early intervention can help, but the degree to which behavior intervention therapy in childhood can improve lives in adulthood is unknown.

The lead investigator of the study commented that neither typical language function, nor typical cognitive functioning, can compensate for “the consequences of having an autism spectrum disorder,” especially when that disorder affects how the person communicates and engages in social situations.

A professor of behavioral science who was not involved in the study expressed his surprise that even though people with atypical autism are “generally better functioning,” they enjoyed no adulthood advantages over those who had more debilitating forms of the disability.

Atypical autism has a reputation for being an “easier” form of the disability to live with, but this is not an accurate representation of the condition. Even as some symptoms may be milder than those of classic autism spectrum disorder, the symptoms that are present can be just as disruptive, both during childhood and into adulthood.

Atypical autism requires the same diligent level of intervention, care, and ongoing therapy as other forms of autism spectrum disorder. The intensity of the treatment will depend on the specifics of the individual case.