The threshold for a diagnosis of ADHD and autism has broadened so much that those with the conditions are virtually indistinguishable from those without it, scientists have suggested.
Experts have identified that the characteristics seen in those with the conditions have changed dramatically over the last decade.
Established risk factors, like congenital problems and low family income, are far less influential today.
Meanwhile doctors are seeing a distinct increase in ‘milder’ cases.
ADHD diagnoses in the UK have shot up around 20-fold over the past two decades, with referrals for specialist appointments up 20 per cent in the last year alone.
Meanwhile, there are an estimated 700,000 autistic Britons. Studies show that autism diagnoses increased by 787 per cent in the UK between 1998 and 2018.
Experts recently raised concerns about the soaring incidence of the developmental problems in the UK, with some accusing doctors of ‘medicalising normal behaviour’.
Last month, Professor Dame Uta Frith, an autism research pioneer, said: ‘When [autism] was first identified in the 1940s, it referred to a small group of children with severe difficulties in social interaction, communication and behaviour.
Danish scientists say children diagnosed in 2012 were far more likely to have traits historically linked to the disorders than those in 2022
‘Over time, the definition has widened to include people with milder traits and no language or learning problems.
‘Today, anyone of any age or intelligence level can be diagnosed with autism if they meet certain criteria.’
The team behind the new study – led by Aarhus University in Denmark – said that ‘traditional risk factors’ are becoming less common in those with a diagnosis.
They highlighted a ‘shift’ in the definition of ‘impairment’ regarding different ‘neurodevelopmental traits’.
‘Milder traits may be more likely to be associated with impairment and diagnosis,’ they wrote in the journal JAMA Psychiatry. ‘This could contribute to increasing incidence.’
Scientists in the study analysed around 71,300 Danish children diagnosed with autism and ADHD between 2012 and 2022.
Over this time, diagnoses jumped from 4,944 to 9,179 – a rise of 86 per cent.
They found that in 2012, children born with a low birth weight had 54 per cent higher odds of an autism or ADHD diagnosis compared to those born at a normal weight.
By 2022, however, this had dropped to just 17 per cent.
The link between family income and a diagnosis also shifted, specifically for ADHD.
At the start of the study, one in four diagnosed children had low-educated mothers, falling to around one in seven by 2022.
In total, the researchers examined 19 characteristics before diagnosis. This included family income, whether parents lived together, parental health and age at birth, as well as use of GPs or psychologists before diagnosis.
Authors of the study said those diagnosed with ADHD or autism became ‘increasingly similar’ in characteristics to people without a diagnosis over the decade.
Autism and ADHD are often closely linked because they are both neurodevelopmental conditions, but they are different.
Autism affects how people communicate, interact with others and experience the world around them, according to the NHS.
Autistic people may also think and process information differently, prefer routines and be more sensitive to sights, sounds, smells or touch.
Meanwhile, ADHD, or attention deficit hyperactivity disorder, affects concentration, activity levels and impulse control.
Symptoms can include being easily distracted or forgetful and struggling to follow instructions.
Authors of the new research stressed that the findings should not be interpreted as showing that ADHD or autism have become less debilitating.
Commenting on the findings, Professor Frith, who was not involved in the research, confirmed that newly diagnosed individuals ‘look far more like their unaffected peers’ these days.
‘The implication of this is that the proportion of mild cases is increasing and severely affected individuals become less visible,’ she added.
