Autism Diagnoses are Rising, but Why?

A new study casts doubt on the autism epidemic

Posted Sep 06, 2015

There is little debate that the number of children being diagnosed with an autistic spectrum disorder has been rising sharply over the past 40 years.  Compared to historical rates around 1975 of 1 in about 5,000, the CDC now estimates that 1 in 68 children (and 1 in 42 boys) meet diagnostic criteria for autism.

The question is no longer if the diagnosis of autism is rising but why.  Those who attempt to answer this question can be placed into two broad camps: 1) those who believe that this increased prevalence is mostly due to an actual rise in the number of new cases, and 2) those who believe that at least the lion’s share of the increased numbers is really an artifact due to things like increased surveillance, a lower threshold for diagnosis, more public awareness, and shifts in diagnostic patterns.

The latter hypothesis was recently investigated by a series of researchers at Penn State University.  Using a publicly available database, they examined state-by-state enrollment statistics for school special education services from the years 2000 to 2010 for over 6 million children.  Of primary interest were trends regarding the number of children who qualified for services due to having an autistic spectrum diagnosis versus qualifying due to other reasons such as intellectual disability or a specific learning disability.

The researchers found that the number of children in special ed because of autism rose 331% from 2000 to 2010.  This was no surprise.  During the same time frame, however, the number of children receiving services for what has labelled an intellectual disability dropped.  Further, the drop in cases of intellectual disability alone could numerically account for nearly two-thirds of the increase in children with autism.  Also important was that the total number of children with any kind of neurodevelopmental disability stayed roughly the same over this time period.

The authors of the study concluded that their data support the idea that the often mentioned rise in autism is substantially due to a reclassification away from diagnoses of intellectual disability or a specific learning disability and toward autism.

This study is unlikely to sway those convinced that much of the diagnostic increase reflects a surge in actual cases due to yet unknown causes.  While vaccines as the driving force behind the increase has been debunked in study after study, potential candidates that have been suggested to account for the increase include environmental toxins and infectious agent exposure, particularly in the prenatal period.  One factor that has been shown to be related to higher rates of autism is the increased age of parents when having children, but this factor can’t account for the entire trend. 

Obviously there is room for some middle ground here.  While this study cannot rule of the possibility that there are more “true” cases of autism than in the past, evidence does seem to be mounting that at least a significant portion of this increase is due to other factors. 

Note:  You can read more about this study on another PT blog by Temma Ehrenfeld

@copyright by David Rettew, MD

David Rettew is author of Child Temperament: New Thinking About the Boundary Between Traits and Illness and a child psychiatrist in the psychiatry and pediatrics departments at the University of Vermont College of Medicine.

Follow him at @PediPsych and like PediPsych on Facebook.