Shocking gender link in autism comes to light

Autism has long been believed to affect male individuals more.

However, a new study from Sweden, published by The BMJ shows that autism may actually occur at comparable rates among males and females both.

The results show a clear female catch-up effect during adolescence, which the researchers say highlights the need to investigate why female individuals receive diagnoses later than male individuals.

Autism spectrum disorder (ASD) has increased over the past three decades, with a high male-to-female diagnosis ratio of around 4:1.

This increase in prevalence is thought to be linked to factors including wider diagnostic criteria and societal changes (e.g., parental age), while the high male to female ratio has been connected with better social and communication skills among girls, making autism more difficult to spot. However so far, no large study has examined these trends.

To address this, researchers used national registers to analyze diagnosis rates of autism for 2.7 million individuals born in Sweden between 1985 and 2022 who were tracked from birth to a maximum of 37 years of age.

During this long follow-up period of more than 35 years, autism was diagnosed in 78,522 (2.8%) of individuals at an average age of 14.3 years.

Diagnosis rates increased every five years throughout childhood, reaching 645.5 per 100,000 person years for male individuals at age 10-14 years and 602.6 for female individuals at age 15-19 years.

However, while male individuals were more likely to have a diagnosis of autism in childhood, female individuals caught up during adolescence, giving a male to female ratio approaching 1:1 by age 20 years.

This is an observational study and the authors acknowledge that they did not consider other conditions associated with autism, such as ADHD and intellectual disability. Nor were they able to control for shared genetic and environmental conditions like parental mental health.

"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,” they wrote.

"These observations highlight the need to investigate why female individuals receive diagnoses later than male individuals," the researchers concluded.