- ADHD is highly heritable (~70%) and polygenic, with rare CNVs; genetic risk implicates early neurodevelopment and frontal cortical circuits.
- There are no diagnostic genetic tests; clinical assessment should prioritise functional impairment, development and family history, and comorbidity.
- Pharmacogenetic evidence supports CYP2D6 genotyping for atomoxetine dosing; routine genetic testing for stimulant selection is not justified.
Can J Psychiatry. 2026 Jun 16:7067437261457230. doi: 10.1177/07067437261457230. Online ahead of print.
ABSTRACT
BackgroundAttention-deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental condition characterized by early-onset inattention, hyperactivity, and impulsiveness. Affecting 5% to 10% of youth and persisting into adulthood in ∼6%, ADHD is frequently discussed in genetic terms by patients and their families, making it essential for clinicians to understand current genetic evidence.ObjectiveTo summarize contemporary genetic findings relevant to ADHD across the lifespan and provide practical guidance for clinicians on assessment, treatment, and psychoeducation.Scope and methodsThis focused narrative review integrates evidence from family and twin studies, genome-wide association studies (GWAS), copy number variants (CNVs), polygenic risk scores (PRS), and Mendelian randomization (MR), as well as pharmacogenetics and studies of gene-environment interplay.FindingsADHD is highly heritable (∼70%), comparable to other major neuropsychiatric conditions. GWAS reveals that thousands of common variants collectively contribute to risk (i.e., polygenic), though each has a small effect. Rare CNVs are more frequent in ADHD than controls and overlap with CNVs in autism. Genetic findings implicate neurodevelopmental pathways expressed in early brain and frontal cortical circuits. ADHD genetic risk correlates with cognitive traits, risk-taking behaviours, and multiple psychiatric and physical health outcomes. Gene-environment correlations and interactions influence risk and course. Pharmacogenetic evidence supports CYP2D6 genotyping for atomoxetine dosing; routine genetic testing for stimulant selection is not justified.Clinical implicationsThere are no diagnostic genetic tests for ADHD. Assessment should prioritize functional impairment, developmental and family history, and comorbidity. Psychoeducation should emphasize modifiable risks and the interplay of genes and the environment. While genetic insights may eventually refine diagnosis and personalized care, current best practice relies on comprehensive clinical evaluation and multimodal management.ConclusionGenetic research confirms ADHD’s neurodevelopmental basis, continuity across the lifespan, and overlap with other neurodevelopmental conditions of childhood. Clinicians can use these insights for counselling and risk monitoring while avoiding over-reliance on genetic testing outside targeted pharmacogenetic use.
PMID:42299664 | DOI:10.1177/07067437261457230
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