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Objectives: We aimed to describe the intellectual ability and ratio of boys to girls with average or higher IQ within autism spectrum disorder (ASD) cases identified in a population-based birth cohort. We hypothesized that research-identified individuals with ASD would be more likely to have average or higher IQ, compared to clinically diagnosed ASD. We also hypothesized the male to female ratio would decrease as the definition of ASD broadened., Methods: ASD incident cases were identified from 31 220 subjects in a population-based birth cohort. Research-defined autism spectrum disorder, inclusive criteria (ASD-RI) was based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision, autistic disorder (AD), Asperger Disorder, and pervasive developmental disorder not otherwise specified criteria. Research-defined autism spectrum disorder, narrow criteria (ASD-RN) was a narrower definition based on Diagnostic and Statistical Manual of Mental Disorders, Fourth Edition, Text Revision AD criteria. Clinical diagnoses of ASD were abstracted from medical and school records. Intellectual ability was based on the last IQ score or on documented diagnoses of intellectual disability if no scores available. Average or higher IQ was defined as IQ ≥86., Results: A total of 59.1% of those with ASD-RI (n = 890), 51.2% of those with ASD-RN (n = 453), and 42.8% of those with clinically diagnosed autism spectrum disorder (n = 187) had average or higher IQ. Within the ASD-RI and ASD-RN groups, boys were more likely than girls to have an average or higher IQ (62.0% vs 51.3% [P = .004] and 54.1% vs. 42.5% [P = .03], respectively)., Conclusion: Our data suggest that nearly half of individuals with ASD have average or higher IQ. Boys with ASD are more likely to have average or higher IQ than girls. Patients with ASD and higher IQ remain at risk for not being identified., Competing Interests: POTENTIAL CONFLICT OF INTEREST: The authors have indicated they have no potential conflicts of interest to disclose., (Copyright © 2021 by the American Academy of Pediatrics.)

Objective: To compare the characteristics of children with attention-deficit hyperactivity disorder (ADHD) who have high intelligence quotient (IQ) versus normal and low IQ through long-term follow-up of children with ADHD from a population-based birth cohort., Methods: Subjects included children with research-identified ADHD (N = 379) from a birth cohort (N = 5718). Full scale IQ scores obtained between ages 6 and 18 years were used to categorize children into 3 groups: Low (IQ < 80), Normal (80 ≤ IQ < 120), and High IQ (IQ ≥ 120). Subjects were retrospectively followed up from birth until emigration, death, or high school graduation/dropout. The groups were compared on demographic characteristics, age at which ADHD case criteria were met, comorbidities, treatment, and school outcomes., Results: There were no significant differences among children with high (N = 34), normal (N = 276), or low IQ (N = 21) and ADHD in numerous characteristics, including median age at which ADHD criteria were fulfilled (9.5, 9.7, and 9.8 years); rates of comorbid learning disorders (85.3%, 78.3%, and 76.2%), psychiatric disorders (47.1%, 50.4%, and 47.6%), and substance abuse (17.6%, 23.6%, and 19.0%); and rates of stimulant treatment (79%, 75%, and 90%). In comparison to children with normal or low IQ, those with high IQ had mothers with higher educational levels (e.g., college graduation rates 44.1%, 11.6%, and 14.3%), and higher reading achievement (median national percentiles on standardized reading tests 77.0, 42.0, and 29.0, p < 0.001)., Conclusions: These findings suggest that ADHD is similar among children with high, normal, and low IQ, although high IQ may favorably mediate some outcomes such as reading achievement. Diagnosis and treatment of ADHD are important for all children, regardless of cognitive ability.