A major study from Sweden's Karolinska Institutet has challenged the widely held belief that autism primarily affects males. The research, published in The BMJ, tracked 2.7 million individuals born between 1985 and 2022 for up to 37 years.
The key finding: while boys are diagnosed with autism more often during childhood, girls experience a steady increase in diagnoses during their teenage years. By approximately age 20, the male-to-female diagnosis ratio approaches 1:1. Overall, 78,522 people (2.8% of those studied) received an autism diagnosis, with an average diagnosis age of 14.3 years.
The gender gap in diagnoses has also been shrinking over time. In older groups (born in the 1980s-1990s), boys were diagnosed at much higher rates. In more recent groups, the difference is significantly smaller.
Why might girls be diagnosed later? Autism diagnostic criteria were originally developed based on how the condition appears in boys. Girls with autism often display different patterns — they may be better at "masking" social difficulties and have fewer obvious repetitive behaviors. As social demands increase in adolescence, masking becomes harder, leading to more diagnoses.
The study has limitations: it's observational (it can't prove why the gap is closing), it didn't account for other conditions like ADHD that often appear alongside autism, and it didn't adjust for genetic or environmental factors. Still, the findings suggest that screening tools may be systematically missing girls and women with autism.