Females may be just as likely to be autistic as males but boys are up to four times more likely to be diagnosed in childhood, according to a large-scale study.
Research led by the Karolinska Institutet in Sweden scrutinised the diagnosis rates of autism for people born in Sweden between 1985 and 2020. Of the 2.7 million people tracked, 2.8% were diagnosed with autism between the ages of two and 37.
They found that by the age of 20, diagnosis rates of men and women were almost equal, challenging previous assumptions that autism is more common among males.
“Our findings suggest that the gender difference in autism prevalence is much lower than previously thought, due to women and girls being underdiagnosed or diagnosed late,” said the lead author, Dr Caroline Fyfe.
The research calculated that in childhood, boys were diagnosed on average nearly three years earlier than girls – the median age at diagnosis was 15.9 for girls, but 13.1 for boys. Overall, boys were three to four times more likely than girls to be diagnosed with autism under the age of 10, although girls were found to “catch up” by the time they were 20, owing to a rapid increase in autism diagnosis during adolescence.
“These observations highlight the need to investigate why female individuals receive diagnoses later than male individuals,” the authors conclude.
The study, published in the BMJ, also found that while gender disparities in diagnosis rates remained pretty consistent over the last three decades for children under 10, they decreased rapidly for all other age groups.
“Findings indicate that the male to female ratio for autism spectrum disorder has decreased over time and with increasing age at diagnosis,” the authors observe.
“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.”
Patient and patient advocate Anne Cary, writing in a linked editorial, said the research supported arguments that it was “systemic biases in diagnosis, rather than a true gap in incidence” that were behind the discrepancy in diagnosis rates.
While the onset of symptoms could be delayed and masking was undoubtedly a factor, the methods and tools to diagnose autism might be biased and need refining, she said. “These biases have meant that a girl who would ultimately have a diagnosis of autism would have a less than third of a chance of receiving a diagnosis before the age of 10 years,” Cary added.
“As autistic girls and women await proper diagnosis, 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.”
Responding to the findings, autism charities said much more needed to be done to tackle gender stereotypes.
Dr Judith Brown, head of evidence and research at the National Autistic Society, said: “Gender should never be a barrier to receiving an autism diagnosis and access to the right support.
“Historically, it was wrongly assumed that autistic people were mostly men and boys, but we now know that women and girls are more likely to ‘mask’ what [are] traditionally thought of as signs of autism, making it harder to identify the challenges they face.
“Misdiagnosed autistic women can develop coexisting mental health difficulties, such as anxiety and depression, as a result of a lack of support and the exhaustion of masking. This is why it’s so vital that the experiences of autistic women and girls are not overlooked, and outdated stereotypes and incorrect assumptions are finally put to rest.”
Jolanta Lasota, chief executive of Ambitious about Autism, said: “Autistic girls have different experiences to autistic boys and have slipped under the radar for far too long.”
By having their needs misunderstood or explained away as something else, “they have missed out on vital support, and in some cases, reached crisis point with their mental health”, she added.
“It is crucial researchers and diagnostic services continue to build understanding of the different presentations of autism in girls and women, and that our support services adapt to accommodate the increasing number of people who we now know need them.”
Dr Conor Davidson, former Royal College of Psychiatrists’ autism champion and clinical lead for Leeds autism diagnostic service, said: “Autism in girls is more likely to go undetected during childhood and signs of the condition might only surface during adolescence or even early adulthood.
“Psychiatrists working in adult neurodevelopmental clinics in the UK have started to see higher numbers of women coming forward than men in recent years. Unfortunately, waiting lists for both child and adult autism assessments are unacceptably long.
“There are many autistic women who have not received a diagnosis, and it is vital that they are able to access a timely assessment and care if they need it.
“Psychiatrists must also be aware of the possibility of autism when they are assessing patients with mental health problems. This can be particularly important for women, whose autism may not have been picked up in childhood.”
