OARacle Newsletter

A Swedish study recently published in BMJ suggests that autism may not be more prevalent in boys than girls. Researchers analyzed autism diagnoses in children born in Sweden between 1985 and 2020. By the end of the study in 2022, the male-to-female ratio was 1.2 and researchers projected that it would be equal at age 20 by 2024. 

Historically, autism has been believed to affect males more than females, most recently at a ratio of 3.4 to 1. As the study authors noted in their article, there are a number of theories as to why males are more often diagnosed with autism and at an earlier age, including a genetic predisposition among males and females masking autistic traits as well as females being diagnosed with co-occurring conditions leading to missed autism diagnoses. Another theory holds that sex bias in research and diagnosis affects the ratio. 

The research team analyzed the health records of 2.7 million individuals born in Sweden between 1985 and 2022 with ongoing follow up as they aged. Over the 35 years of observation, 78,522 people were diagnosed with autism, or 2.8 percent of the individuals in the study. The average age of diagnosis was 14.3 years. 

Diagnosis rates rose as the individuals aged. Diagnoses for males peaked between 10 and 14 years old reaching 645.5 diagnoses per 100,000 person years. (A person year combines the number of participants in a study and the duration of time each person is followed.) For females, the peak occurred between the ages of 14 and 19, with 602.6 diagnoses per 100,000 person years. 

By age 20, the cumulative male to female ratio was 1.2. The research team projected that the male-to-female ratio would be 1:1 at age 20 by 2024. 

“These findings indicate that the male-to-female ratio for autism has decreased over time and with increasing age at diagnosis. This male-to-female ratio may therefore be substantially lower than previously thought, to the extent that, in Sweden, it may no longer be distinguishable by adulthood,” wrote Caroline Fyfe, PhD, lead author, and her co-authors.

“These observations highlight the need to investigate why female individuals receive diagnoses later than male individuals,” they added.

In a BMJ editorial in the same issue, Anne E. Cary, a patient and patient advocate in Boulder, Colorado, describes the age effect as striking, arguing that it seems to point to systemic biases in diagnosis. “These biases have meant that a girl who would ultimately have a diagnosis of autism would have less than a third of a chance of receiving a diagnosis before the age of 10 years.” While this could be because onset of traits is delayed in girls, it could also be because “the assessment tools contain sex biases and need reworking.”

Underdiagnosing and misdiagnosing girls and women creates “barriers to appropriate interventions, supports, and accommodations afforded to correctly diagnosed autism in women,” Cary wrote. Furthermore, she wrote they are “likely to be (mis)diagnosed with psychiatric conditions, especially mood and personality disorders, and they are forced to self-advocate to be seen and treated appropriately: as autistic patients, just as autistic as their male counterparts.”

In a Medpage Today article, Diana Schendel, PhD, of the A.J. Drexel Autism Institute at Drexel University in Philadelphia, noted that the United States doesn’t have a comparable study. However, the CDC’s Autism and Developmental Network, which follows 4- to 8-year-olds, shows enormous variances in the sex ratio across locations, indicating, she said, “a lot of local factors going on that impact who’s being referred, and who’s being diagnosed and reported with autism.” 

Sherri Alms is the freelance editor of The OARacle, a role she took on in 2007. She has been a freelance writer and editor for more than 20 years.