In March 2020, the Centers for Disease Control (CDC) released new statistics related to the diagnosis and monitoring of children with Autism Spectrum Disorder (ASD) in the United States. As reported in these findings, there’s a difference in the diagnosis and prevalence of ASD found in girls and boys. At this time, it’s unclear if these differences are because the characteristics of ASD are different in girls, if how we diagnose ASD in girls is different, or if it’s a combination of factors. Below is a summary of what we know and don’t know about gender differences in ASD.
Autism is more common in boys.
According to the Centers for Disease Control’s (CDC) Autism and Developmental Disabilities Monitoring (ADDM) Network, 1 in 54 children have a diagnosis of Autism Spectrum Disorder. Of those children, there is a large disparity between the number of boys and girls who receive a diagnosis of ASD. Averaged across all national monitoring sites, 1 in 34 boys (29.7 in 1,000) were diagnosed with ASD as compared to 1 in 144 girls (6.9 in 1,000) identified with ASD. The CDC reports a male-to-female autism prevalence ratio of 4.3 to 1.
ASD statistics are changing.
It’s important to note, however, that these diagnostic rates for boys and girls have changed rapidly in the past 20 years. The CDC statistics show that in the year 2000, the diagnostic rate for ASD was about 1 in 150 children. At that time, the male-to-female autism prevalence ratio was 16:1. Today, ASD diagnoses occur at much higher rates, and the gender gap is now down to 3-4 boys for every 1 girl diagnosed. Both the differences in prevalence rates and the changes in these rates over time can help answer the question “Is Autism Different in Girls and Boys?”
Why is autism more prevalent in boys than girls?
Scientists and researchers around the globe continue to examine the gender-based differences in autism prevalence. Despite advances in autism research, it’s still unclear if the differences are related to disparities in diagnostic rates, or if autism actually impacts boys and girls differently. While we don’t have a definitive answer, there are several hypotheses about why ASD may vary by gender:
Diagnostic rates are higher for developmental disorders in boys.
One way researchers have questioned ASD diagnostic rates is by examining other developmental disorders.
The same gender differences that exist in ASD can also be identified in other related developmental disorders, including ADHD. Additional evidence suggests that when ADHD prevalence rates are studied among a population of adults, that women are diagnosed at more similar rates as men, suggesting that the disorder is not more common in boys, it’s simply more commonly overlooked in girls.
Research and Diagnostic Criteria Were Developed Largely With Boys
Another factor that researchers suggest contributes to diagnostic differences in boys and girls is that much of the research done to develop our current diagnostic tests and tools were created with a population of boys. If the tools we use to diagnose ASD were developed based on the available group of children known to have ASD, then it follows that the population would disproportionately favor the symptoms and characteristics identified in boys.
Researchers continue to examine if these types of diagnostic biases exist in the current instruments we use to diagnose ASD in children. While more research is needed, girls currently identified with ASD may have symptoms that more closely fit ASD symptoms that occur in boys, not necessarily what is representative of symptoms in all girls.
Female genetic protective effects
Some researchers suggest that fewer girls may be diagnosed with ASD because of genetic protective effects.
In the 1980s, researchers at the University of Michigan found that girls with ASD have more close relatives with ASD on average than boys. This led to a decades-long examination of the genetics of ASD and what’s now known as the female genetic protective effect.
Many genetic markers have been shown to influence the expression of autism in children. Some studies have shown that female genetic makeup may offer some ‘protection’ from ASD, because a higher number of genetic markers are required in females than males to reach the threshold for diagnosis. Other studies suggest that girls may be more resistant to the mutations that trigger ASD.
Autism symptoms are different in boys and girls
While researchers are still unsure about how genetic factors contribute to ASD, it’s also possible that the differences in diagnostic rates are because of how autism symptoms are expressed vary. Girls diagnosed with ASD have been shown to more frequently be impacted by a low intellectual level than boys. Girls have also been shown to have fewer restrictive and repetitive behaviors than boys, one of the hallmark symptoms of ASD. Finally, in studies where teachers report student symptoms of ASD, male students have been found to have higher rates of externalized behaviors like aggression and social issues.
What more needs to be studied?
Even though scientists and researchers have some hypotheses about why autism appears to be different in boys than girls, so much of what we know about ASD and gender is unknown. Studies continue to be conducted around the globe focusing on these and other unanswered questions related to diagnosis and genetics:
● What are the genetic factors that contribute to ASD?
● Are girls more resistant to the genetic mutations and influences that contribute to ASD? If there are genetic ‘protective effects,’ what are they and how do they operate?
● If we understand these inherited mutations that contribute to ASD, what can we learn from how they are passed between parents and children?
● Are the differences in ASD prevalence actually related to archaic diagnostic criteria that favor boys?
● Are the symptoms of ASD found more commonly in boys (aggression, ADHD, social disruption, etc.) seen as more ‘troublesome’ or ‘problematic’ to teachers and caregivers than the symptoms more commonly present in girls?
● Do we better educate parents and caregivers of boys to be on the look-out for concerns and leave behind girls in the process?
● If we know more about gender differences, both genetic and diagnostic, how can that help us provide better services and care to children with ASD?
If the past 20 years of statistics and reporting have been any indication of the future, it’s expected that in the upcoming decades, what we know and understand about the gender differences in ASD will only grow. By bolstering our understanding of these differences, practitioners and parents can help more children access the services they need.
Amy Sippl
Applied Behavior Analysis | Saint Cloud State University
Bachelor of Arts (B.A.), Psychology | University of Minnesota
May 2020
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