Autism rates have risen dramatically over the past several decades. In the 1960s and 70s, autism was considered a rare condition, affecting about 1 in 2,000 children.
Today, current estimates indicate 1 in every 44 children has autism spectrum disorder (ASD). This amounts to a nearly 80-fold increase in prevalence over the last 50+ years.
Understandably, many parents and concerned citizens want answers around this upward trend.
In exploring the data and research, it becomes evident the reasons behind rising autism rates are diverse and complex.
A Change in Diagnostic Criteria
One significant factor is the change to diagnostic criteria over time. Autism was first added as a separate diagnostic category in the DSM-III in 1980. Since then, the criteria have expanded to include a broader range of symptoms and severity levels.
Most notably, Asperger's syndrome and pervasive developmental disorder (PDD-NOS), which were previously considered distinct conditions, were folded into the autism spectrum in the DSM-5 revision.
Researchers estimate this expanding definition may account for roughly 60% of the increase in prevalence. Children at the milder end, who likely would not have been identified as autistic in the past, are now able to be accurately diagnosed.
Greater Public Awareness
In addition to the diagnostic changes, autism awareness among parents, doctors, educators and the general public has increased substantially since the 1970s.
Organizations like Autism Speaks have delivered important information into the hands of families, helping them recognize early red flags. Pediatricians are now more informed about autism, improving their ability to make referrals for evaluations during well-child visits.
The portrayal of autistic characters in TV shows and movies has also boosted public knowledge. Overall, this greater awareness has enabled earlier detection and driven more parents to seek out testing when they have concerns.
Improved Screening and Diagnostic Tools
Hand-in-hand with autism awareness, the tools available to detect and diagnose autism have advanced considerably. Standardized screening questionnaires allow consistent testing across different settings.
Diagnostic methods too have progressed to include detailed interviews, direct observation of behaviors, evaluations of development and communication, and objective measures of social, motor and cognitive skills.
These evidence-based tools are better able to identify high-functioning autism and milder variants that may have been overlooked in the past.
Earlier and more meticulous diagnosis translates into earlier intervention, which can dramatically improve outcomes for children.
The Impact of Advanced Parental Age
Multiple studies have identified parental age as a risk factor for having a child with autism, particularly for fathers over 50. Compared to dads under 30, fathers over 50 have nearly twice the risk of having a child with autism.
Researchers speculate that genetic mutations occurring spontaneously over time in parental germ cells may be a factor. As more couples wait longer to have children, this effect of advanced paternal age may influence autism prevalence.
However, it's important to note that parental age only explains a small percentage of autism cases.
Exploring Potential Environmental Contributors
Many studies are also investigating the role of environmental exposures in autism, including air pollution, pesticides, heavy metals and other chemical toxins.
The hypothesis is that certain exposures, especially during key windows of embryonic and fetal development, may interact with genetic susceptibilities to affect normal brain development.
While more research is needed, the environmental factor would help explain some of the variability in autism rates across different geographic regions.
Changes in Reporting Methods
It's also true that how autism data is collected and reported has changed over the decades. In the 1960s and 70s, methods to track prevalence were not consistent.
Diagnostic substitution - placing children in the autism category who would previously have been given a different diagnosis - also affects rates.
Additionally, the DSM-5 brought several previously separate diagnoses under the umbrella autism spectrum disorder, increasing numbers. While not fully explanatory, changes in reporting do account for a portion of the upward trend.
The Need for More Research
While many contributing factors to increased autism rates have been identified, unknown causes almost certainly remain.
There are still gaps in understanding gene-environment interactions, the impact of broader diagnostic criteria, and the precise degree to which different factors are at play.
Going forward, research taking a multifaceted approach will be essential to gaining answers around the autism epidemic.
However, the increased prevalence also reflects progress in awareness, detection and services for individuals living with autism spectrum disorder.