For decades researchers have thought of autism as a predominantly male disorder but experts now say it may affect as many girls as it does boys.
The prevalence of the spectrum disorder has increased over the past thirty years, with around four times as many boys diagnosed than girls.
But the study of more than 2.5million children, who were tracked for decades, found that whilst boys are more likely to receive a diagnosis during childhood, girls catch up during adolescence with diagnostic rate levelling out by the age of 20.
Experts said the findings are ‘timely’ and ‘important’, supporting what autism researchers have known for a long time: its markedly undiagnosed in women.
Publishing their findings in The BMJ, the researchers said: ‘These observations highlight the need to investigate why female individuals receive diagnoses later than male individuals.’
The findings align with recent research which suggest current practices fail to recognise autism in girls, with Ann Cary, a patient and patient advocate, commenting that women are ‘likely to be misdiagnosed with psychiatric conditions.’
She added that as is stands autistic women are ‘forced to self-advocate to be seen and treated appropriately: as autistic patients, just as their male counterparts.’
The study led by Karolinska Institutet, Sweden, involved 2.7million people born in Sweden between 1985 and 2022, who were followed up for around 35 years.
According to researchers, autism is not necessarily more common in boys – it’s just diagnosed earlier
Over the period, 78,522 cases were diagnosed at around 14-years-old. Diagnostic rates increased steadily with age during childhood and was most common in boys aged 10-14 and girls aged 15-19-years old.
By age 20, there was no significant difference in diagnostic rates between the sexes.
Autism is a neurodevelopmental condition which people have from the moment they are born, but because it exists on a spectrum some will be diagnosed in childhood whilst in others it may not be spotted until much later.
It can present as differences in social communication and rigid and repetitive behaviours – which can result in those affected becoming socially isolated, increasing the risk of mental and physical health problems.
The researchers cited a number of theories as to why autism tends to be viewed as a predominately male disorder – including the so-called female protective effect where girls require a high genetic burden than boys for autistic behaviours to become noticeable.
They also suggested the difference in diagnosis rate could be explained by girls’ ability to mask autistic traits by mimicking peers in social interactions, and diagnostic criteria leaning towards a male bias.
As such, autism-related behaviours may not be noticeable until social interactions become more complex in adolescence and beyond.
But they ultimately concluded the male-to-female ratio shows a ‘substantial catch-up effect overtime,’ suggesting that autism is not in fact a male disorder, but rather boys show the classic signs at a younger age leading to earlier diagnosis.
However they acknowledge that whilst other studies have shown similar results the demographic of this study was limited and did not account for shared genetic and environmental factors or other conditions associated with autism, like attention deficit hyperactivity disorder (ADHD) and intellectual disability.
Commenting on the findings, Professor Dame Uta Frith, an expert in cognitive development at University College London, said: ‘The headline “Rates of Autism in girls and boys may be more equal than previously thought” is seriously misleading.
‘The authors rightly ask why it is that females tend to be diagnosed later than males. I wonder whether the late diagnosed females reflect the emergence of a new subgroup of the autism spectrum.’
Dr Laura Hull, who was not involved in the current study, agreed that whilst the use of population-level healthcare records means the data are not influenced by self-reporting, there may be other factors such as co-occurring mental health conditions which influence diagnostic rates which were not accounted for.
She added: ‘Diagnosis rates are still changing and it remains to be seen whether the male-to-female ratio will continue decreasing, will stabilise or even will increase again as we continue to “catch up” with diagnosis of girls and women who were missed.’
Dr Rachel Moseley, from Bournemouth University, highlighted that either way, the ‘under-diagnosis of autism, like ADHD, should be of serious concern.’
She said: ‘What we know about undiagnosed autistic people is that being undiagnosed is often associated with severe difficulties and ever suicidality.’
The findings come following Wes Streeting’s call for an independent review into soaring demand for mental health, ADHD and autism services after a warning of an ‘over diagnosis’ of conditions, in December last year.
As of March last year, figures show there are around 91,000 people aged between 10 and 25-years-old currently awaiting a referral.
Some experts have repeatedly blamed growing awareness of the spectrum disorder, which was only widely diagnosed as its own condition this century.
This has led to a ‘backlog’ of cases, particularly among women and girls who were less likely to be diagnosed in the past.
