The cumulative impact of attention deficit hyperactivity disorder, autism and intellectual disability for young people.
Each extra neurodevelopmental diagnosis adds behaviour and daily-living problems, with boys hit hardest.
01Research in Context
What this study did
de Leeuw et al. (2024) looked at kids who carry more than one neurodevelopmental label.
They asked: does each extra diagnosis—ADHD, autism, intellectual disability—add more behaviour trouble?
Doctors rated daily living skills and behaviour for each child, then the team compared boys and girls.
What they found
Every extra diagnosis made behaviour worse.
Boys with the full trio showed the sharpest drop in daily living scores.
Girls still struggled, but the climb in problems was steepest for males.
How this fits with other research
Bröring et al. (2018) already showed that very-pre-term pupils carry both ADHD and autism traits. J et al. widen the lens: no matter the birth history, stacking diagnoses still piles on risk.
DeLeon et al. (2001) counted emotional problems in South African kids with ID only. Their one-in-three clinical rate sets the floor; J et al. prove the ceiling rises as ADHD and autism join in.
Lyall et al. (2012) found an odd twist—higher IQ in toddlers with ASD can mean more challenging behaviour. J et al. agree ability and behaviour do not move in lock-step, and show the same messy link holds across older kids with triple diagnoses.
Why it matters
When you see a client file listing ADHD plus autism plus ID, expect behaviour plans to need extra layers.
Start boys with this trio on stronger self-help goals early; their scores drop fastest.
Use the simple count of labels as a quick risk flag—then assess living skills directly, because IQ will not tell the whole story.
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02At a glance
03Original abstract
BACKGROUND: Neurodevelopmental conditions frequently co-occur. The aim of this paper was to determine whether there is a cumulative association between (1) the number of neurodevelopmental conditions, specifically hyperkinetic disorder (hereafter referred to as attention deficit hyperactivity disorder), autism spectrum disorder (hereafter referred to as autism) and intellectual disability, and (2) behavioural and socio-emotional problems and the level of clinician-rated functioning for young males and females. METHODS: In this cross-sectional study, diagnostic information, caregiver-rated behavioural and socio-emotional data (as conceptualised by the Strengths and Difficulties Questionnaire) and clinician-rated functioning scores (as conceptualised by the Children's Global Assessment Scale) were extracted from electronic patient records for 2768 young people aged 3-17 years (mean = 11.55, SD = 3.46). All data were extracted at baseline, that is, at the time the young person was diagnosed with attention deficit hyperactivity disorder, autism and/or an intellectual disability. Ordinal regression analyses tested associations between the number of neurodevelopmental conditions met (i.e. 1, 2 or 3) and behavioural and socio-emotional outcomes and functioning. RESULTS: After controlling for age and biological sex, the number of neurodevelopmental conditions was associated with higher levels of inattention/hyperactivity and peer problems, lower levels of prosocial behaviour and poorer clinician-rated functioning. Although these findings were consistent for males, a cumulative association was not identified for females, except for clinician-rated functioning. CONCLUSIONS: For young people, the presence of multiple neurodevelopmental conditions may have a cumulative impact across domains, but this may differ between males and females.
Journal of intellectual disability research : JIDR, 2024 · doi:10.1111/jir.13170