Single-cell RNA sequencing study reveals the potential role of the RPS26 gene in attention deficit hyperactivity disorder.

Attention deficit/hyperactivity disorder (ADHD) is a common neurodevelopmental disorder in children and adolescents. Due to the limited availability of postmortem brain tissue, most gene expression studies in ADHD have relied on bulk RNA profiling of total white blood cells (WBCs). However, this approach obscures cell-type-specific expression patterns and limits insights into the roles of distinct leukocyte subsets in ADHD pathophysiology. Single-cell RNA sequencing (scRNA-seq) offers a solution to these challenges but has not yet been widely applied to investigate ADHD biomarkers. Emerging evidence suggests that ADHD may be associated with increased risk of cardiovascular disease, in which monocytes and macrophages are known to play key pathological roles. In this study, we aimed to explore the potential link between ADHD and cardiovascular disease by focusing on monocyte/macrophage biology. Using scRNA-seq to analyze WBC samples from a pair of dizygotic twins discordant for ADHD, we identified 12 distinct immune cell types and discovered several differentially expressed genes, including RPS26 in monocytes. Quantitative PCR (qPCR) validation confirmed significantly reduced RPS26 expression in both WBCs and monocytes from individuals with ADHD. Further in vitro assays revealed that RPS26 knockdown suppressed monocyte proliferation, potentially by promoting monocyte apoptosis. Moreover, RPS26 knockdown impaired monocyte-to-macrophage maturation and altered the 28S to 18S RNA ratio. Collectively, these findings suggest that RPS26 plays a regulatory role in monocyte development and differentiation, which may help explain the elevated cardiovascular risk reported in individuals with ADHD. In summary, this study highlights the functional importance of RPS26 and provides new insights into a potential molecular link between ADHD and cardiovascular disease.