Until now, it was believed that autistic disorder is more common in boys. It turns out that girls are more difficult to diagnose: they have better developed social and communication skills, which often “mask” the symptoms. This is the conclusion reached by the authors of an article published last week in The British Medical Journal.
A recent study found a clear “catch-up effect” among adolescent girls, researchers reported in The BMJ. These findings highlight a need to investigate why autism spectrum disorders are diagnosed in females later than in males, they said.
Over the past three decades, the prevalence of autism spectrum disorders (ASD) has increased significantly. According to the US Centers for Disease Control and Prevention, autism occurs in 1 in 31 children, and it is on average 3.4 times more common in boys than in girls. According to data from England, the rate among children is 1.76%, up from 1.57% in 2009.
According to WHO estimates, the global prevalence of ASD among children is 1%, which is higher than the 2012 rate of 0.62%. However, as WHO notes, many countries lack the resources to identify and register cases of the disorder.
Most diagnoses are made in childhood by the age of 10. Currently, for every girl diagnosed with ASD, there are three boys with the disorder.
To analyze diagnosis rates over the life course, researchers in Sweden and the United States tracked 2.7 million individuals born in Sweden between 1985 and 2022, from birth to a maximum age of 37. Overall, ASD was diagnosed in 2.8% of individuals at an average age of around 14. Diagnosis rates were highest among boys at ages 10 to 14 and among girls at ages 15 to 19. But by age 20, the male to female ratio had evened out at nearly 1:1, the researchers found.
These findings and other recent research suggest “current practices are failing to recognize autism in many women until later in life, if at all,” patient advocate Anne Cary wrote in an accompanying editorial.
The study did not account for genetic or environmental factors, or for other conditions associated with autism, such as attention deficit hyperactivity disorder and intellectual disability, which might have played a role in patients’ diagnoses.
Dr. Rachel Moseley of Bournemouth University in the UK, who was not involved in the study, says the extended follow-up of young people is important because studies of children may miss autistic features which are already present in males but not yet visible in females.
This difference in diagnosis rates has also been attributed to better social and communication skills among girls, making autism more difficult to spot. “And what we know about undiagnosed autistic people is that being undiagnosed is often associated with severe difficulties and even suicidality – so underdiagnosis… should be of serious concern,” Moseley said.