1. Health
You can opt-out at any time. Please refer to our privacy policy for contact information.

Discuss in my forum

What Is Atypical Autism?


Updated April 28, 2014

Written or reviewed by a board-certified physician. See About.com's Medical Review Board.

Question: What Is Atypical Autism?
What Is Atypical Autism?
Answer: Atypical autism is another name for one of the five official autism spectrum diagnoses: pervasive developmental disorder not otherwise specified (PDD-NOS).

Autism spectrum is another name for pervasive developmental disorders (PDDs), a category of diagnoses with certain symptomatic similarities.

The PDD category includes five discrete diagnoses: Asperger syndrome, PDD-NOS, autistic disorder, Rett syndrome and childhood disintegrative disorder.

Oh -- and there is no official diagnosis called "autism."

So if your child receives a diagnosis of "atypical autism," which means he is officially diagnosed with PDD-NOS, he has too few symptoms to be diagnosed with autistic disorder or Asperger syndrome, and the wrong symptoms to be diagnosed with Rett syndrome or Childhood Disintegrative Disorder. Yet he has received an official medical diagnosis which means that he has significant pervasive developmental disorders.

If all this seems about as clear as mud to you, you're not alone.

Perhaps the question now arises: if my child has a diagnosis of "atypical autism" or PDD-NOS, is he autistic? The answer is yes... and no.

In order to receive a diagnosis of PDD-NOS or atypical autism, a child must exhibit many -- but not all -- of the symptoms of an autism spectrum disorder (or PDD). Since the PDD-NOS diagnosis is included under the umbrella of pervasive developmental disorders, and PDD is essentially a synonym for autism spectrum disorders, it is correct to say that a person with PDD-NOS has an autism spectrum disorder -- but Incorrect to say that such a person has autistic disorder (which is a discrete diagnosis within the autism spectrum, but is different from PDD-NOS).

If a child has atypical autism, and is not officially "autistic," are his symptoms milder?

In fact, a diagnosis of PDD-NOS doesn't necessarily mean that the child's symptoms are milder or less disabling, only that they don't completely fall within the diagnostic criteria for another related disorder such as Asperger syndrome or autistic disorder. In other words, it's quite possible to have an atypical autism/PDD-NOS diagnosis and be severely disabled.

Interestingly, though, many children and adults with atypical autism/PDD-NOS diagnoses do in fact have relatively mild symptoms. A study comparing individuals with atypical autism/PDD-NOS diagnoses to individuals with other, more specific autism spectrum diagnoses came up with this conclusion:

RESULTS: In terms of level of functioning measures, the PDD-NOS children had scores that were between those of the children with autism and those of the children with AS. In contrast, the PDD-NOS group had fewer autistic symptoms, especially repetitive stereotyped behaviors, than both the autism and AS groups (chi2 = 11.06, p =.004). Children with PDD-NOS could be placed into one of three subgroups: a high-functioning group (24%) who resembled AS but had transient language delay or mild cognitive impairment; a subgroup resembling autism (24%) but who had late age of onset or too severe cognitive delays or were too young to potentially meet the full diagnostic criteria for autism; and a group (52%) not fulfilling the criteria for autism because of fewer stereotyped and repetitive behaviors.

While the categories of the autism spectrum are very difficult to distinguish, in a sense it really doesn't matter which diagnosis your child receives. That's because the treatments recommended for your child's developmental differences are likely to be very similar no matter what the official autism spectrum diagnosis: intensive behavioral and/or developmental therapy, along with speech, occupational and physical therapies. As your child grows a bit older, he or she will also almost certainly be recommended to some form of social skills therapy as well.


Allen DA, Steinberg M, Dunn M, Fein D, Feinstein C, Waterhouse L, Rapin I. "Autistic disorder versus other pervasive developmental disorders in young children: same or different?" Eur Child Adolesc Psychiatry. 2001 Mar;10(1):67-78.

National Institute of Child Health and Human Development. Autism Spectrum Disorders (ASDs)Fact Page.

Walker DR, et al. "Specifying PDD-NOS: a comparison of PDD-NOS, Asperger syndrome, and autism." J Am Acad Child Adolesc Psychiatry. 2004 Feb;43(2):172-80.

  1. About.com
  2. Health
  3. Autism Spectrum Disorders
  4. Autism 101
  5. Types of Autism
  6. Atypical Autism, or Pervasive Developmental Disorders (PDDs)

©2014 About.com. All rights reserved.

We comply with the HONcode standard
for trustworthy health
information: verify here.