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What is Atypical Autism?

April 16, 2024

Diagnosing mental conditions can be tricky, and autism is no exception. Over the years, our understanding of autism and developmental disorders, in general, has evolved a lot, but that means it can be hard to keep track of all the subcategories and definitions that have popped up along the way. 

What is Atypical Autism?

One term you may have heard of is “atypical autism”. What exactly does that mean, and how is it different from classic autism spectrum disorder? Let’s take a look.

What does atypical autism mean?

A person has atypical autism when they display some symptoms of autism spectrum disorder (ASD), but not enough to fit a diagnosis. Atypical autism is another term for pervasive developmental disorder-not otherwise specified (PDD-NOS). 

The “not otherwise specified” part of PDD-NOS explains the purpose of this diagnosis—to catch the people who don’t quite align with other conditions.

It has also been called subthreshold autism, indicating that it doesn’t fully meet the diagnostic criteria of ASD.

Pervasive developmental disorders

So, if atypical autism is an unspecified pervasive developmental disorder, what exactly are those? 

According to the International Classification of Diseases, Tenth Revision (ICD-10), PDDs are a “category of developmental disorders characterized by impaired communication and socialization skills”. Classic autism falls under this category, as does asperger syndrome, Rett’s syndrome, childhood disintegrative disorder, and PDD-NOS/atypical autism.

The Diagnostic and Statistical Manual of Mental Disorders (DSM), which sets the standard for psychiatry in the United States, used to include these conditions under pervasive developmental disorders as well. But the DSM V, the fifth and most recent version of the DSM, changed things up when it comes to autism.

An outdated diagnosis

The ICD-10 still lists atypical autism as a valid diagnosis, but not everyone agrees. The DSM V, which was published in 2013, got rid of the term “pervasive developmental disorders” completely. PDD-NOS/atypical autism and the other conditions under that umbrella were instead folded into the broader label of autism spectrum disorders.

The next version of the ICD, ICD-11, is following the DSM V’s lead, though it’s not set to go into effect until 2022 or later in some countries. Soon, PDD-NOS/atypical autism won’t be considered an up-to-date diagnosis in much of the world.

It’s not surprising that the diagnosis of atypical autism is phasing out. The Encyclopedia of Autism Spectrum Disorders calls it “poorly defined”, adding that this results “in inconsistencies and variability in the way in which the diagnosis is applied”.

When can atypical autism be diagnosed?

Technically, most doctors, at least in the United States, no longer diagnose children with atypical autism. But just because atypical autism isn’t considered its own condition anymore, this doesn’t mean that the people who met that description no longer exist. There will always be individuals who don’t completely match the symptoms of autism as most people think of it.

Signs of autism spectrum disorder can become evident at an early age. Autistic children are usually diagnosed around three years old, though they can be diagnosed younger. Parents should keep an eye out for symptoms such as slow development in speech and nonverbal communication, mild cognitive delays, a lack of eye contact, lack of response to one’s name, and more. Check out our article Signs of Autism in Babies and Toddlers for more symptoms that can help you detect autism early.

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Sometimes, children would be diagnosed with atypical autism because their symptoms appeared later than usual. So, don’t necessarily count autism spectrum disorder out if your child starts showing signs past toddlerhood.

Difference between ASD and atypical autism

The last edition of the DSM in which atypical autism appeared, the DSM IV, required patients to meet three criteria for an autism diagnosis: impairments in social interaction, impairments in communication, and repetitive behaviors. 

A child diagnosed with atypical autism/PDD-NOS only needed to have symptoms in two of those categories, but one of them had to be social interaction. In other words, a child with atypical autism could either have trouble with social skills and communication or social skills and repetitive behaviors. The DSM IV also specified that schizophrenia, schizotypal personality disorder, and avoidant personality disorder should be ruled out before a diagnosis of PDD-NOS could be given.

Today, of course, ASD looks different in the DSM V. According to this manual, children with autism should have deficits in…

  • Social behavior—they may have difficulty in initiating or maintaining conversations
  • Nonverbal communication—they may struggle to understand the body language, eye contact, and facial expressions of others, and/or not show these behaviors themselves, or do so in abnormal ways
  • Development and understanding of relationships—they may not understand how to adjust behaviors for different contexts, relate to friends, or show much interest in bonding with others

Additionally, patients with autism should show at least two of these four repetitive patterns:

  • Repetitive body movements or speech
  • Insistence on routines and rituals
  • Very narrow focus on certain interests
  • Unusual responses to sensory input (either overreacting or underreacting to lights, smells, temperatures, sounds, etc.)

Clearly, the DSM V’s diagnostic criteria for autism have expanded quite a bit. So what happens to a child who previously would have been diagnosed with atypical autism, but doesn’t meet the DSM V’s current requirements for ASD? 

A 2014 study analyzed a sample of children with an autistic disorder to see how many matched the new DSM V standard. It found that 63% of children with PDD-NOS did, while 32% were a better fit for social communication disorder, which is similar to but distinct from autism. The remaining kids had symptoms closer to other health conditions, like anxiety disorder or ADHD.

Even though PDD-NOS as an individual disorder no longer exists, that study shows that the majority of people with this form of autism do belong on the autism spectrum. Atypical autism involves the same classic autism symptoms, such as delays in motor skills, cognitive skills, language skills, et cetera; they just may be milder and somewhat less disruptive to everyday life.

Is atypical autism the same as asperger syndrome?

Like atypical autism, asperger syndrome was previously perceived as a high-functioning form of ASD. Now, neither label is used by doctors, at least in the United States. The ICD-10 retains both diagnoses, though they will phase out in the next edition.

Even so, asperger’s was never considered the same as atypical autism. The DSM IV defined it by “impairment in social interaction” and “stereotyped patterns of behavior, interests, and activities”, but without delays in language or cognitive development.

PDD-NOS was, of course, defined only by the fact that it wasn’t anything else, including asperger’s.

In conclusion

Autism spectrum disorder is, well, a spectrum. It encompasses a wide range of symptoms and abilities, and every autistic person is unique.

If you think your child meets some of the diagnostic criteria for autism, it’s worth consulting a doctor. Even if his/her functioning isn’t greatly impaired, people with atypical autism can still face struggles.

Research has shown that early intervention tends to be very beneficial for autistic kids. Receiving a diagnosis of autism in early childhood will enable you to pinpoint what areas your child struggles in, whether it’s speech, relationship-building, etc. From there, you can access treatment and therapies to manage those symptoms and work on creating a plan for your child’s education if he/she needs support in school. 

It can be hard to hunt for a diagnosis and feel like none are quite the right fit. Whether it’s autism, social communication disorder, or something else, you and your child’s experiences are valid. 

In the world of psychiatry, autism spectrum disorder and atypical autism may not officially be distinct anymore. But there’s still a place for people and families who experience autism a little differently.


Centers for Disease Control and Prevention. (2000). Handout IV: DSM-IV-TR Diagnostic Criteria for Pervasive Developmental disorders. Centers for Disease Control and Prevention. https://www.cdc.gov/ncbddd/actearly/autism/case-modules/pdf/diagnosis/DSM-IV-TR-Diagnostic-Criteria-for-Pervasive-Development-Disorders.pdf

Centers for Disease Control and Prevention. (2020, June 29). Diagnostic Criteria for 299.00 Autism Spectrum Disorder. Centers for Disease Control and Prevention. https://www.cdc.gov/ncbddd/autism/hcp-dsm.html 

Gray, K. M. (2018). Atypical Autism. In Encyclopedia of Autism Spectrum Disorders. Springer. https://link.springer.com/referenceworkentry/10.1007%2F978-1-4614-6435-8_1635-3

ICD 10 Data. (2021). 2021 ICD-10-CM Diagnosis Code F84.9. ICD 10 Data. https://www.icd10data.com/ICD10CM/Codes/F01-F99/F80-F89/F84-/F84.9

Kim, Y. S., Fombonne, E., Koh, Y.-J., Kim, S.-J., Cheon, K.-A., & Leventhal, B. L. (2014). A Comparison of DSM-IV Pervasive Developmental Disorder and DSM-5 Autism Spectrum Disorder Prevalence in an Epidemiologic Sample. Journal of the American Academy of Child and Adolescent Psychiatry, 53(5), 500-508. https://www.jaacap.org/article/S0890-8567(14)00044-6/fulltext 

World Health Organization. (2021). 6A02 Autism spectrum disorder. ICD-11 for Mortality and Morbidity Statistics. https://icd.who.int/browse11/l-m/en#/http%3a%2f%2fid.who.int%2ficd%2fentity%2f437815624 

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