Is the inattentive subtype of ADHD different from the combined/hyperactive subtype?
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Updated: Jun 20, 2026

Using Brain Activation (nir-HEG/Q-EEG) and Execution Measures (CPTs) in a ADHD Assessment Protocol
Published on: April 1, 2018
Natalie Grizenko1, Michael Paci, Ridha Joober
1McGill University. grinat@douglas.mcgill.ca
Objective:
To compare the ADHD combined/hyperactive subtype (ADHD/CH) to the ADHD inattentive subtype (ADHD/I) on the level of comorbidity, treatment response, and possible etiological factors.
Method:
A total of 371 clinically referred children diagnosed with ADHD aged between 6 and 12 years are recruited for a double-blind, placebo-controlled trial of methylphenidate. Comorbidity, treatment response, and stress during pregnancy are assessed for each participant. Genotyping is done for the DAT, DRD4, and 5-HTT genes. Mothers report smoking or alcohol consumption during their pregnancy and their child's birth weight.
Results:
The ADHD/CH children show both a higher frequency of conduct disorder and good response to treatment, are exposed to more moderate stress during their mothers' pregnancy, and show a higher frequency of L/L genotype for the 5-HTT-linked polymorphic region.
Conclusion:
The significant differences found between the ADHD/CH and the ADHD/I subtypes raise the possibility that the two may be separate disorders.
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