Why Are Boys Diagnosed with Autism More Than Girls?

Do you worry your child might have autism spectrum disorder? If you have a daughter, pay particular attention to clues. Girls may exhibit more subtle symptoms, which could lead to a missed diagnosis.

Boys have long been diagnosed with autism at a much higher rate than girls, but that gap is narrowing as scientific understanding of autism spectrum disorder grows.

Among the more recent discoveries: Girls with autism may have fewer or more subtle versions of the stereotypical behaviors autistic boys so often exhibit, and they may have learned social skills like eye contact and smiling to mask their symptoms and avoid diagnosis.

Because of these differences, boys have long been diagnosed at about four times the rate of girl. But that is changing. One study published in 2015 found that the true male-to-female ratio is closer to 3:1 than 4:1 and another in 2017 noted: “There appears to be a diagnostic gender bias, meaning that girls who meet criteria for ASD are at disproportionate risk of not receiving a clinical diagnosis.”

As understanding of female autism spreads, more girls and women are being diagnosed. In 2020, the Autism Spectrum Diagnosis Disabilities Monitoring Network reported that, for the first time, the percentage of girls diagnosed with autism topped 1 percent — still well below 4.3 percent of boys.

This is not to suggest that unbiased diagnosis will eventually produce equal percentages of boys and girls with autism. Because autism has a large genetic component, the chromosomal differences between the sexes mean boys will always outnumber girls with an ASD diagnosis.

Genes and Chromosomes

ASD is a neurological and developmental condition that affects how people interact with others, communicate, learn and behave. It was first identified as "infantile schizophrenia" and later carried other names being redefined in 2013 as autism spectrum disorder, which recognized the varying degrees of impairment. Some people with autism never speak. Others run companies.

While science has yet to identify one single cause of autism, it has determined that it is about 83 percent due to genetics:  Research has linked ASD to mutations on more than 100 genes, which then can be passed from one generation to the next.

Girls and women may enjoy a female protective effect, a theory that suggests females may require a greater number or a larger magnitude of risk factors like gene mutations to manifest autism symptoms compared to males. This effect is thought to be related to the fact that females have two X chromosomes, while males have one X and one Y.

Early Diagnosis of ASD

Although autism can be diagnosed at any age, it is described as a “developmental disorder” because symptoms generally appear in the first two years of life. Early symptoms typically fall into three categories:

Social communication. Slow or no language development and making odd sounds or an odd tone of voice.

Social interaction. Examples include no or limited eye contact or smiling, and not responding  to their name.

Repetitive behaviors. This includes self-stimulation by repetitive actions or sounds, or rituals like lining up objects in a particular order.

Quick developmental screenings frequently offered in child-care settings are an important first step. If such a screening suggests developmental delays, a specialist — a developmental pediatrician, child psychologist or speech pathologist, for example — should take a closer look.

The specialist may observe the child and give a structured test and ask the parents or caregivers questions. With this formal evaluation, trained professionals can predict autism at 18 months and make a reliable diagnosis by age 2, before children begin showing gender-based differences.

An early diagnosis before a child starts school could lead to interventions that allow an autistic child to develop the social and language skills needed to start school on time and prepare for lifelong success, an opportunity needed equally by boys and girls with autism.

By School Age

Despite the benefits of early diagnosis and intervention, most autistic children are not diagnosed until they begin school, by which time they and their peers are expressing rigid gender-based stereotypes. That may be why the behavior of a loud and rowdy autistic boy catches attention while that of a quiet girl expressing subtler symptoms may not.

In other words, the model we’ve been using to diagnose ASD is a male model, but we are changing that. Specialists at all levels are being trained to recognize symptoms in boys and girls because a diagnosis provides clarity, enhances understanding, and opens access to support, resources and services that can be life-changing.