This population-based longitudinal study (Generation R, Netherlands) tracked behavioral and emotional problems in 4,643 children from ages 1.5 to 15 years, comparing three operationalizations of Mild Intellectual Disability (MID1: IQ ≤75; MID2: IQ ≤75 + adaptive functioning impairment; MID3: IQ ≤85 + adaptive functioning impairment) against propensity score-matched controls across 8 psychopathology domains.
All three MID definitions were associated with elevated behavioral and emotional problems vs. matched controls. The broadest definition (MID3, IQ ≤85 + adaptive functioning impairment) showed the highest burden — ADHD (β=0.37), affective (β=0.25), autistic (β=0.25), ODD (β=0.40), and somatic problems (β=0.25) were all significantly elevated at baseline (all pFDR <0.001), with ADHD, affective, and ASD problem gaps **widening** over time. Children with borderline IQ (75–85) appeared to carry more mental health burden than those with lower IQ (MID1/MID2).
- Adaptive functioning items partially overlapped with CBCL outcome measures, potentially inflating associations for MID2 and MID3. - No standardized adaptive functioning tool (e.g., Vineland) was used, and no clinical judgment was incorporated, which may misclassify MID cases. - Unmeasured confounders (parenting, genetics, comorbid diagnoses) and selection bias from missing WISC data limit generalizability.
Screen children with borderline intellectual functioning (IQ 75–85) for ADHD, anxiety, and mood problems early — this group may carry a higher and growing mental health burden than children with lower IQ, yet often has less access to specialized care. When evaluating MID, the choice of diagnostic criteria (IQ alone vs. IQ + adaptive functioning) meaningfully changes which children are identified and what psychopathology profiles are found.
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