For generations, autism has been widely perceived as a condition that predominantly affects males, but groundbreaking new research suggests this long-held assumption may be fundamentally flawed. A comprehensive study indicates that autism spectrum disorder likely affects girls and boys in equal measure, with diagnostic disparities primarily reflecting when individuals are identified rather than true prevalence.
Landmark Study Challenges Decades of Medical Assumption
Researchers from Sweden's Karolinska Institutet conducted an extensive analysis involving 2.7 million people born between 1985 and 2022, tracking their health records for approximately 35 years. Their findings, published in The BMJ, reveal a striking pattern: while boys are diagnosed with autism more frequently during childhood, girls catch up during adolescence, with diagnostic rates essentially equalising by the age of 20.
Over the study period, 78,522 autism cases were diagnosed at an average age of 14 years. The research demonstrated that diagnostic rates increased steadily with age throughout childhood, peaking most commonly in boys aged 10-14 and girls aged 15-19. By early adulthood, however, there was no significant difference in diagnostic rates between the sexes.
Why the Diagnostic Disparity Exists
The researchers proposed several explanations for why autism has historically been viewed as a predominantly male disorder. One prominent theory is the so-called female protective effect, suggesting girls may require a higher genetic burden than boys for autistic behaviours to become noticeable to observers.
Additionally, experts point to girls' greater ability to mask autistic traits by mimicking peers during social interactions, combined with diagnostic criteria that have traditionally leaned toward male presentations of autism. These factors mean autism-related behaviours may not become apparent until social interactions become more complex during adolescence and beyond.
Ann Cary, a patient and advocate, commented that women are "likely to be misdiagnosed with psychiatric conditions" and that autistic women are often "forced to self-advocate to be seen and treated appropriately: as autistic patients, just as their male counterparts."
Understanding Autism Spectrum Disorder
Autism is a neurodevelopmental condition present from birth, though its manifestation varies widely across what is known as the spectrum. Some individuals receive diagnoses in childhood, while others may not be identified until much later in life. The condition typically presents as differences in social communication alongside rigid and repetitive behaviours, which can lead to social isolation and increased risk of mental and physical health challenges.
Importantly, being autistic does not mean having an illness or disease requiring a cure. Rather, it reflects a different way of brain functioning that is present throughout an individual's lifetime. While the exact causes remain unclear, research indicates genetic factors play a significant role, and autism is definitively not caused by bad parenting, vaccines, diet, or infectious agents.
Expert Responses and Cautions
Professor Dame Uta Frith, an expert in cognitive development at University College London, offered a measured response to the findings, noting that while the research raises important questions about diagnostic timing, the headline suggestion of equal prevalence "is seriously misleading." She questioned whether later-diagnosed females might represent "the emergence of a new subgroup of the autism spectrum."
Dr Laura Hull, who was not involved in the study, acknowledged the strength of population-level healthcare data in avoiding self-reporting biases but noted that factors like co-occurring mental health conditions could influence diagnostic rates in ways not fully accounted for in the research.
"Diagnosis rates are still changing," Dr Hull observed, "and it remains to be seen whether the male-to-female ratio will continue decreasing, will stabilise, or even will increase again as we continue to 'catch up' with diagnosis of girls and women who were missed."
Broader Implications for Healthcare Systems
Dr Rachel Moseley from Bournemouth University emphasised that regardless of the exact prevalence figures, "the under-diagnosis of autism, like ADHD, should be of serious concern." She highlighted that "being undiagnosed is often associated with severe difficulties and even suicidality" among autistic individuals.
These findings emerge amid growing pressure on mental health and neurodevelopmental services. In December, Shadow Health Secretary Wes Streeting called for an independent review into soaring demand for autism and ADHD services following warnings about potential over-diagnosis. Current figures show approximately 91,000 people aged 10-25 awaiting referrals as of March last year.
Some experts attribute increasing diagnosis rates to growing awareness of autism spectrum disorder, which only gained widespread recognition as a distinct condition this century. This heightened awareness has created a significant backlog of cases, particularly among women and girls who were less likely to be diagnosed in previous decades.
The Swedish researchers acknowledged limitations in their study, noting that while other research has shown similar patterns, their demographic scope was limited and did not account for shared genetic and environmental factors or co-occurring conditions like ADHD and intellectual disability. Nevertheless, their work represents a significant step toward understanding autism's true prevalence across genders.
