In early October, a study conducted by the Centers for Disease Control and Prevention found that autism rates in the U.S. are much higher than previous estimates. According to CDC statistics, published in the medical journal Pediatrics, approximately 1 in 100 children fall into what’s known as the autism spectrum, up from the previous estimate of 1 in 150.

Autism is the most commonly diagnosed developmental disorder. A higher level of awareness by physicians and the general public, coupled with a much more expansive definition of what behaviors fall into the autism spectrum, are two factors which may be contributing to the increase in diagnoses.

Greg Allen is an associate professor in the Department of Educational Psychology at the University of Texas at Austin. As part of his research, Allen, a licensed psychologist who specializes in neuropsychological assessment, is studying the role of the cerebellum in autism, and how brain abnormalities are linked to the disorder’s behaviors and symptoms. He recently received a three-year $750,000 grant from the National Institutes of Health.

Recent studies suggest that autism rates are much higher than previously thought. What do you attribute this to? Increased awareness? An ever-widening spectrum (Asperger’s syndrome, Rett syndrome, childhood disintegrative disorder, and Pervasive Developmental Disorder Not–Otherwise Specified)? Possible misdiagnosis or overdiagnosis?

I think there are a lot of factors. There’s no question that part of the increase [is due to] our widening definition of the spectrum, as you put it. In 1994 a major event happened in the understanding of autism diagnoses when Asperger’s disorder first appeared in DSM-IV (the Diagnostic and Statistical Manual of Mental Disorders). Before that Asperger’s was a concept in the field of autism but wasn’t widely recognized as a disorder or diagnosis.

In the DSM there are prevalence numbers for various disorders—for autism they were much lower than they are now. For what is technically called autism, the rate was two to five cases per 10,000 individuals, while rates for Asperger’s were not available at the time. So then what happened, the field drifted toward thinking more along the lines of autism spectrum disorders, which include both autism and Asperger’s and to which current prevalence rates typically refer. So, obviously a major widening of what we consider the spectrum to be . . . contributed to the increased rates. I think it is very important that we try to understand how much of the increase is attributable to a broadening of the spectrum as well as increased awareness in order to understand the potential contribution of other factors that may be of concern.

What is the difference between autism and Asperger’s?

There are a couple of important distinctions between autism and Asperger’s. In autism, you have three main categories of symptoms—impairment in communication, impairment in social interaction, and restricted and repetitive interests and behaviors. What’s different about Asperger’s is that it doesn’t involve a delay in language development. Also, you can’t have any clinically significant delays in cognitive development.

Does that mean Asperger’s is not as serious as autism?

Not necessarily. You hear the terms “high-functioning” and “low-functioning” that refer to the abilities of people in the autism spectrum. With autism, you see all levels of functioning. In contrast, anyone with Asperger’s is by definition in the high-functioning range due to the lack of clinically significant delays in language or cognitive development.

In the spectrum, does everything fall under autism or Asperger’s?

Both of these disorders fit into the broader category of Pervasive Developmental Disorders (PDD). In the DSM, there is a term “Not Otherwise Specified (NOS)” used to refer to individuals who meet some but not all categories for a particular disorder, and PDD-NOS is another diagnosis within the autism spectrum.

How do you make that kind of diagnosis?

There are limitations of DSM and diagnosing disorders based on behavior. Mental disorders are characterized by clusters of symptoms and not every person fits well into a specific category. There’s definite interest in the field in focusing more on individual symptoms or symptom clusters rather than the broad range of symptoms that make up a disorder. For example, the phenotype approach, where you consider the individual behavioral or biological features of a disorder and then try to link those features to their genetic basis (or genotype).

And there is no autism gene yet, right?

There is evidence for many genes that may play a role in autism, but a single specific gene has not been identified. I think the fact that we have autism, Asperger’s, and PDD-NOS really just scratches the surface of how many different disorders there actually are in the autism spectrum. Lots of research still needs to be done to understand the different subtypes. If we can separate autism spectrum disorders into more subtypes, we’re certain to do a better job of understanding the factors that cause these disorders, genetic or otherwise. I think it’s safe to say, though, that it’s not going to be a simple answer. Current thinking in genetics research is that autism is a multiple gene disorder, unlike some illnesses that are cause by one specific gene.

Could there be overdiagnosis of these disorders?

There’s certainly a risk any time you have a disorder that is so difficult to diagnose. You could have both overdiagnosis and underdiagnosis. When you combine a disorder that’s very challenging to diagnose with massive increased awareness of that disorder, naturally one of those risks inherent in that situation would be overdiagnosis. Particularly when you consider the overlapping symptoms that many behavioral disorders have.

With more children being diagnosed with autism or Asperger’s syndrome, do you believe the disorder is linked to genetics and environmental factors, like heavy metals and pesticides?

Certainly there’s a natural concern with the increased prevalence as dramatic as seen in autism spectrum disorders with what’s going on in the environment. What are all the different factors leading to the increase in prevalence rates? I think there are some who look at it . . . and accept it all as being some environmental factor causing this. I definitely would caution against that. Going back to the first thing we talked about, it’s important to understand that some of the increase is definitely accounted for by the broadening of the spectrum and increased awareness. However, I also think there’s an increased acceptance in the autism research community that we need to look at other potential factors, such as environmental causes or triggers that interact with a genetic predisposition.

What will the $750,000 grant over three years that you recently received from NIH allow you to do?

My focus is on studying the role of the cerebellum in autism. There have been many brain regions studied and proposed to be involved in autism and, like behavior in autism, the underlying brain abnormalities seem to be pretty heterogeneous. However, one of the most consistent findings is abnormality in the cerebellum. My research is aimed at trying to link the cerebellar anatomic abnormalities with behavior. Specifically, I’m using magnetic resonance imaging (MRI) to investigate how connections between the cerebellum and other brain systems may be affected in autism. The cerebellum communicates with a wide range of brain systems, and a breakdown in this communication may be a vehicle through which cerebellar abnormalities contribute to the broad range of behaviors and symptoms seen in autism. Understanding the brain basis of the behaviors and symptoms of autism spectrum disorders will bring us closer to understanding their cause.

What’s the prognosis today for a child with autism or Asperger’s? And how critical is early diagnosis and intervention?

Most of the accepted treatments are behavioral in nature. There are some medications people have used to help control some of the symptoms of autism, but most interventions are behavioral. There’s a view that the earlier you can identify children who have autism or may be at risk, that you can intervene in their behavior. So there’s a push in pediatrics to identify kids as early as possible.

About two thirds of people [within the autism spectrum] are in the range of what would be considered mental retardation. However, this too is controversial because there are many who feel that standard measures of IQ do not apply in autism given the challenges that people with autism face (e.g., delay in or lack of spoken language).

Why is autism more common in boys than in girls?

It’s definitely more common in boys. In fact, when you focus on the more high-functioning individuals, the ratio of boys to girls within the spectrum is in the neighborhood of ten to one. It’s not known why this is the case, though it seems to point to the role of genetics.

It seems like there are definite trends in psychological illnesses and corresponding diagnoses. Is autism the next Attention Deficit Disorder?

I think this goes back to your earlier question about overdiagnosis, which is a definite risk as people become more and more aware of autism spectrum disorders. This points to the importance of standardizing our approaches to diagnosis and being sure that our clinicians are well educated on what is and what is not an autism spectrum disorder.