Fasting serum levels of RXR-α, PPAR-γ, and PPAR-γ coactivator 1α were quantified via enzyme-linked immunosorbent assay.<h4>Results</h4>Generalized linear models adjusted for demographic characteristics, ADHD medications, and clinical symptoms revealed that adolescents with ADHD had reduced RXR-α levels (p = 0.001; Cohen's d = 0.47) compared with neurotypical adolescents. This evidence concerns the gene RXRA and attention deficit-hyperactivity disorder.